1 Introduction

Photosynthesis is a fundamental biological process that converts solar energy into chemical energy, sustaining life on Earth. This process is primarily carried out by plants, algae, and cyanobacteria, which utilize two major protein-cofactor complexes known as photosystems I (PSI) and II (PSII) (Jordan et al., 2001; Dau and Zaharieva, 2009; Nelson and Junge, 2015). These photosystems are embedded in the thylakoid membranes of chloroplasts and work in tandem to capture light energy and drive the synthesis of carbohydrates from water and carbon dioxide (Dau and Zaharieva, 2009). The efficiency of photosynthesis is remarkable, with PSI and PSII achieving near-perfect quantum efficiency in converting absorbed photons into chemical energy (Nelson and Junge, 2015; Croce and Amerongen, 2020). This high efficiency is attributed to the sophisticated arrangement of pigments and proteins within the photosystems, which facilitate rapid and efficient energy transfer and electron transport (Collini et al., 2010; Pan et al., 2020).

Optimizing the structures of photosynthetic protein complexes is crucial for enhancing the efficiency of light energy conversion. The detailed atomic structures of PSI and PSII have provided insights into the mechanisms of light capture and energy transfer, revealing potential targets for optimization (Jordan et al., 2001; Pan et al., 2020). For instance, the arrangement of chlorophyll and carotenoid molecules within the light-harvesting complexes (LHCs) plays a significant role in determining the efficiency of energy transfer to the reaction centers (Pan et al., 2020; Shang et al., 2023). By modifying these structures, it is possible to improve the overall efficiency of photosynthesis, which has significant implications for renewable energy technologies. Enhanced photosynthetic efficiency could lead to the development of biohybrid devices for solar energy conversion and solar fuel synthesis, leveraging the natural mechanisms of photosynthesis (Liu et al., 2019).

This study explores the current understanding of the structural and functional aspects of photosynthetic protein complexes, with a focus on their optimization for improved light energy conversion efficiency. We will examine the latest structural data on PSI and PSII, highlighting the key features that contribute to their high efficiency. Additionally, we will discuss recent advances in synthetic biology and bioengineering that have enabled the creation of novel photosystems with enhanced energy harvesting capabilities. By synthesizing findings from multiple studies, this study seeks to provide a comprehensive overview of the strategies for optimizing photosynthetic protein complexes and their potential applications in renewable energy technologies.

2 Photosynthetic Protein Complexes: Structure and Function

2.1 Description of key photosynthetic protein complexes

Photosynthesis in plants, algae, and cyanobacteria is driven by four major multi-subunit membrane-protein complexes: Photosystem I (PSI), Photosystem II (PSII), the cytochrome b6f complex, and ATP synthase.

Photosystem I (PSI): PSI is a large pigment-protein complex that plays a crucial role in the light-dependent reactions of photosynthesis. It is responsible for generating the most negative redox potential in nature, which is essential for the conversion of light energy into chemical energy. PSI is composed of multiple subunits and cofactors, including chlorophylls, carotenoids, and iron-sulfur clusters, which facilitate efficient light capture and electron transfer (Jordan et al., 2001; Nelson and Yocum, 2006; Qin et al., 2015).

Photosystem II (PSII): PSII is another essential complex that catalyzes the photo-oxidation of water, producing oxygen as a byproduct. It consists of a core complex surrounded by light-harvesting complexes (LHCs) that capture and transfer light energy to the reaction center. The PSII core includes several subunits and cofactors, such as chlorophylls, pheophytins, and a manganese-calcium cluster, which are involved in the water-splitting reaction (Nelson and Yocum, 2006; Croce and Amerongen, 2011; Suga et al., 2014; Chukhutsina et al., 2015).

Cytochrome b6f Complex: This complex acts as an intermediary in the electron transport chain, facilitating the transfer of electrons between PSII and PSI. It also contributes to the generation of a proton gradient across the thylakoid membrane, which is used to drive ATP synthesis (Nelson and Yocum, 2006; Yadav et al., 2017).

ATP Synthase: ATP synthase is responsible for the synthesis of ATP from ADP and inorganic phosphate, utilizing the proton gradient generated by the electron transport chain. This enzyme complex is crucial for providing the energy required for various cellular processes (Nelson and Yocum, 2006).

2.2 Structural components and their roles in light energy conversion

The structural components of these photosynthetic protein complexes are intricately designed to optimize light energy conversion:

Chlorophylls and Carotenoids: These pigments are essential for capturing light energy. Chlorophylls absorb light primarily in the blue and red regions of the spectrum, while carotenoids absorb in the blue-green region, extending the range of light that can be utilized for photosynthesis. The arrangement of these pigments within the protein complexes ensures efficient energy transfer to the reaction centers (Jordan et al., 2001; Qin et al., 2015).

Reaction Centers: The reaction centers of PSI and PSII are specialized protein complexes where primary charge separation occurs. In PSII, the reaction center includes the D1 and D2 proteins, which bind the primary electron donor (P680) and the primary electron acceptor (pheophytin). In PSI, the reaction center includes the PsaA and PsaB proteins, which bind the primary electron donor (P700) and the primary electron acceptors (A0, A1, and FX) (Nelson and Yocum, 2006; Croce and Amerongen, 2011; Suga et al., 2014).

Iron-Sulfur Clusters and Quinones: These cofactors play critical roles in electron transport. In PSI, iron-sulfur clusters (FX, FA, and FB) facilitate the transfer of electrons from the reaction center to ferredoxin. In PSII, plastoquinone (QA and QB) accepts electrons from pheophytin and transfers them to the cytochrome b6f complex (Jordan et al., 2001; Suga et al., 2014).

2.3 Mechanisms of energy transfer and electron transport

The mechanisms of energy transfer and electron transport in photosynthetic protein complexes are highly efficient and tightly regulated:

Excitation Energy Transfer: Light energy absorbed by the antenna pigments is transferred to the reaction centers through a process known as excitation energy transfer. This process involves the transfer of excitation energy from one pigment molecule to another until it reaches the reaction center, where it drives the primary charge separation (Chukhutsina et al., 2015; Qin et al., 2015).

Electron Transport Chain: The electron transport chain consists of a series of redox reactions that transfer electrons from water to NADP⁺, forming NADPH. In PSII, the oxidation of water generates electrons, protons, and oxygen. The electrons are transferred to plastoquinone, which carries them to the cytochrome b6f complex. From there, electrons are transferred to plastocyanin and then to PSI, where they are used to reduce NADP⁺ to NADPH (Nelson and Yocum, 2006; Suga et al., 2014; Chukhutsina et al., 2015).

Proton Gradient and ATP Synthesis: The transfer of electrons through the cytochrome b6f complex is coupled with the translocation of protons across the thylakoid membrane, creating a proton gradient. This gradient drives the synthesis of ATP by ATP synthase, providing the energy required for the Calvin cycle and other cellular processes (Nelson and Yocum, 2006).

These structural and functional insights into photosynthetic protein complexes highlight the intricate mechanisms that plants, algae, and cyanobacteria use to convert light energy into chemical energy efficiently. Understanding these processes at a detailed level can inform efforts to optimize photosynthesis for improved energy conversion efficiency.

3 Current Challenges in Photosynthetic Efficiency

3.1 Limitations in natural photosynthetic systems

Natural photosynthetic systems, while highly efficient in their native environments, face several inherent limitations. One significant challenge is the selective spectral coverage due to the specific natural pigmentation of photosynthetic proteins, which restricts the range of light wavelengths that can be effectively utilized for energy conversion (Liu et al., 2020). Additionally, the structural complexity and variability of photosystem complexes, such as PSI and PSII, across different organisms can lead to inefficiencies in energy transfer and charge separation processes (Croce and Amerongen, 2020). The need for a highly organized assembly of photofunctional chromophores and catalysts within proteins to optimize solar energy conversion further complicates the development of fully functional artificial systems (Wasielewski, 2009).

3.2 Factors affecting the efficiency of light energy conversion

Several factors influence the efficiency of light energy conversion in photosynthetic systems. The arrangement and connectivity of pigments within light-harvesting complexes play a crucial role in determining energy transfer rates and overall efficiency (Croce and Amerongen, 2020). For instance, the dynamic regulation of light-harvesting systems through state transitions in plants and green algae helps balance energy distribution between PSI and PSII, optimizing photosynthetic activity under varying light conditions (Shang et al., 2023) (Figure 1). Moreover, the structural design of photosystems, such as the PSI-LHCII supercomplex, facilitates efficient light harvesting and energy transfer by forming specific pigment networks (Su et al., 2017). The quantum coherence observed in some photosynthetic proteins also suggests that long-range quantum coherence can enhance light-harvesting efficiency by enabling more efficient energy transfer between molecules (Collini et al., 2010).

Figure 1 Structures of PSI-LHCI-LHCII from plants and green algae (Adopted from Shang et al., 2023) Image caption: (a) Overall structure of ZmPSI-LHCI-LHCII (PDB code: 5ZJI). (b) Overall structure of CrPSI-LHCI-LHCII (PDB code: 7DZ7). (c) Modeled PpPSI-LHCI-LHCII based on the PpPSI-L structure (PDB code: 8HTU). The PSI-LHCI parts are displayed as a cartoon, with Lhcas, PsaO, and ZmPsaN shown in different colors and labeled. The other core subunits are shown in white. The LHCII trimers are displayed as a surface and distinguished by different colors. The Lhcb9 and Lhca proteins in the outer LHCI belt from PpPSI-L, which are not included in the modeled PpPSI-LHCI-LHCII, are shown as a ribbon. (d) Comparison of the membrane-spanning regions of the three PSI-LHCI-LHCII complexes. LHCIIs (CrLHCII-1) are displayed as a cartoon, and other parts are shown as a ribbon. ZmPSI-LHCI-LHCII, CrPSI-LHCI-LHCII, and modeled PpPSI-LHCI-LHCII are displayed in magenta, yellow, and cyan, respectively. Arrows indicate the deflection of LHCII relative to the membrane. The phosphorylated N-terminal regions of LHCIIs are highlighted in a red box. (e) Structural comparison of the first five residues from ZmLhcb2, CrLhcbM1, and PpLhcbM2. (f) Zoomed-in view of the binding sites of the N-terminal regions of CrLhcbM1 and CrLhcbM5 in CrPSI-LHCI-LHCII. The phosphorylated Thr residues are highlighted with spheres (Adapted from Shang et al., 2023)

3.3 Impact of environmental stressors on photosynthetic performance

Environmental stressors, such as high light intensity, temperature fluctuations, and nutrient availability, can significantly impact photosynthetic performance. High light conditions, for example, can lead to the detachment of moderately bound LHCIIs in PSII to down-regulate light harvesting and prevent photodamage (Su et al., 2017). Additionally, the structural and functional integrity of photosynthetic complexes can be compromised under stress conditions, affecting their ability to capture and convert light energy efficiently (Jordan et al., 2001). The adaptability of photosynthetic organisms to different ecological niches has led to structural changes in photosystems, which can influence their performance under varying environmental conditions (Amunts and Nelson, 2009). Understanding these stress responses and their impact on photosynthetic efficiency is crucial for optimizing photosynthetic systems for improved light energy conversion.

By addressing these challenges and leveraging insights from natural photosynthetic systems, researchers can develop more efficient artificial photosynthetic systems for practical solar fuels production and other applications.

4 Strategies for Structural Optimization

4.1 Genetic engineering approaches to modify protein complexes

Genetic engineering offers a powerful toolkit for modifying photosynthetic protein complexes to enhance their efficiency. By manipulating the genetic code, researchers can introduce specific mutations that optimize the spatial arrangement and functional properties of these complexes. For instance, RNA interference (RNAi) technology has been employed to down-regulate the light-harvesting complex (LHC) gene family in green algae, resulting in reduced energy losses through fluorescence and heat, and thereby increasing the photosynthetic quantum yield and efficiency under high-light conditions (Mussgnug et al., 2007). Additionally, the evolutionary adaptation of photosystem I (PSI) structures in various organisms, such as cyanobacteria and eukaryotic algae, highlights the potential for genetic modifications to improve light-harvesting capabilities and overall efficiency (Bai et al., 2021).

4.2 Computational modeling and structural predictions

Computational modeling plays a crucial role in predicting and optimizing the structures of photosynthetic protein complexes. Techniques such as molecular modeling and non-equilibrium statistical descriptions help in understanding the dynamics of light-harvesting complexes and their efficiency (Pachon and Brumer, 2012). First-principles modeling protocols have been successfully applied to predict the electronic properties of pigment-protein complexes, such as the Fenna-Matthews-Olson (FMO) complex, with high precision. These models can uncover fine details of excitonic structures and energy transfer mechanisms, which are essential for designing more efficient photosynthetic systems (Kim et al., 2020). Computational protein design (CPD) also addresses the challenge of identifying optimal protein sequences through combinatorial optimization, further aiding in the structural refinement of photosynthetic complexes (Allouche et al., 2014).

4.3 Techniques for enhancing stability and function of photosynthetic complexes

Enhancing the stability and function of photosynthetic complexes is vital for improving their performance in artificial systems. Self-assembly strategies, such as those involving π-stacking and metal-ligand interactions, have been explored to create supramolecular structures that integrate light harvesting with charge separation and transport (Wasielewski, 2009). The use of DNA as a structural matrix element has also been shown to improve the stability and photocurrent of protein-based light-harvesting electrodes, demonstrating the potential of hybrid approaches combining biological and synthetic components (Stieger et al., 2016). Additionally, the development of modular chromophore-catalyst assemblies inspired by natural photosynthetic reaction centers offers a pathway to create stable and efficient artificial photosynthetic systems. These assemblies can be optimized for light-harvesting and redox catalysis, providing insights into the impact of structural environments on electron transfer and charge separation (Mulfort and Utschig, 2016).

By leveraging genetic engineering, computational modeling, and innovative assembly techniques, researchers can significantly enhance the efficiency and stability of photosynthetic protein complexes, paving the way for more effective light energy conversion systems.

5 Case Studies and Experimental Evidence

5.1 Engineering photosystem II for improved electron transport

Photosystem II (PSII) plays a crucial role in the initial stages of photosynthesis by absorbing light and converting it into chemical energy through charge separation. Recent studies have focused on understanding and enhancing the efficiency of electron transport within PSII. For instance, a theoretical investigation into the dynamics of light harvesting in the dimeric PSII core complex revealed that multiple excitation energy transfer (EET) pathways exist between subunits of PSII, ensuring robust light harvesting and efficient energy transfer (Hsieh et al., 2019). Additionally, a structure-based model of energy transfer in PSII supercomplexes demonstrated that the kinetics of light harvesting involve substantial contributions from both excitation diffusion through antenna pigments and transfer to the reaction center, highlighting the complexity and efficiency of the process (Bennett et al., 2013). These insights provide a foundation for engineering PSII to optimize electron transport and improve overall photosynthetic efficiency.

5.2 Modifying light-harvesting complexes to increase light absorption

Light-harvesting complexes (LHCs) are integral to capturing light energy and funneling it to the reaction centers of photosystems. Modifying these complexes can significantly enhance light absorption. For example, the structural and spectroscopic analysis of photosystem complexes from oxygenic photosynthetic organisms has shown that the arrangement of pigments and their connectivity are crucial for efficient energy transfer (Croce and Amerongen, 2020). Furthermore, the isolation and characterization of a large Photosystem I-Light Harvesting Complex II (PSI-LHCII) supercomplex in Arabidopsis revealed the presence of an additional Lhca1-a4 dimer, which enhances the light absorption capacity of PSI (Crepin et al., 2019) (Figure 2). These findings underscore the potential of structural modifications in LHCs to boost light absorption and improve photosynthetic performance.

Figure 2 Single-particle electron microscopy (EM) analysis (Adopted from Crepin et al., 2019) Image caption: (a) Negative-staining single-particle EM analysis of the eluted PSI-LHCII fraction revealed that the main component was a well-characterized particle consisting of PSI and a single LHCII trimer (Kouřil et al., 2005; Galka et al., 2012). (b) The atomic model of PSI-LHCII (5ZJI) (Pan et al., 2018) is superimposed on the EM density map, illustrating the positions of LHCII and the Lhca1-4 subunits (view from the stromal side). (c) EM analysis of the PSI-6LHCI-LHCII fraction identified a previously undescribed particle with a large extra density on the PsaB-PsaI-PsaH side. (d) The atomic model of PSI-LHCII is superimposed to emphasize the location of the extra density in the PSI-6LHCI-LHCII complex. (e) Biochemical data suggest that the extra density corresponds to an Lhca1-4 dimer (in red), indicating an interaction between this extra dimer, the PSI core, and the LHCII trimer. (f) The atomic model of the PSI of Chlamydomonas reinhardtii (6JO5) (Suga et al., 2019) is superimposed, maintaining the same positions for the core and internal Lhca as in plant PSI, to display the position of the additional algal Lhca dimer (Lhca2-9, in yellow). In algae, this extra dimer is positioned differently compared to the extra density in the Arabidopsis PSI-6LHCI-LHCII complex. Note that the outer row of algal Lhca proteins is absent in plant PSI. See Figure S3 for further details on EM analysis (Adapted from Crepin et al., 2019)

5.3 Enhancing the stability of cytochrome b6f complex under stress conditions

The cytochrome b6f complex is a critical component of the photosynthetic electron transport chain, linking PSII and PSI. Enhancing its stability under stress conditions is vital for maintaining efficient photosynthesis. Research has shown that the structural stability of light-harvesting complexes, such as CP47, is essential for their function. A study using a multiscale quantum mechanics/molecular mechanics approach demonstrated that the structural stability of CP47 is significantly affected when isolated from PSII, leading to rapid refolding and loss of certain pigments (Sirohiwal et al., 2021). This highlights the importance of maintaining the integrity of protein complexes within their native environment to ensure stability and functionality. Additionally, the role of protein phosphorylation and Mg²⁺ in influencing light harvesting and electron transport in chloroplast thylakoid membranes has been investigated, revealing that these factors can modulate the interactions and stability of photosynthetic complexes (Harrison and Allen, 1992). These insights provide strategies for enhancing the stability of the cytochrome b6f complex under various stress conditions, thereby improving the resilience and efficiency of the photosynthetic apparatus.

By leveraging these case studies and experimental evidence, researchers can develop targeted strategies to optimize photosynthetic protein complex structures, ultimately improving light energy conversion efficiency in photosynthetic organisms.

6 Innovative Approaches and Emerging Technologies

6.1 Use of synthetic biology to create artificial photosynthetic systems

Synthetic biology offers a promising avenue for the development of artificial photosynthetic systems by enabling the construction of novel pathways and the optimization of existing ones. This approach can significantly enhance photosynthetic efficiency, which is crucial for improving crop productivity and meeting global food, fiber, and fuel demands (Creatore et al., 2013). By integrating biological components with synthetic materials, researchers have been able to create biohybrid systems that combine the specificity of biological catalysts with the tunability of synthetic nanomaterials. These systems can efficiently channel reductant energy into specific chemical transformations, thereby optimizing solar-to-chemical conversion (Brown and King, 2019). Additionally, synthetic biology has been employed to engineer living cells with enhanced electron transport capabilities, paving the way for next-generation biophotovoltaic technologies (Schuergers et al., 2017).

6.2 Advances in nanotechnology for structural modification

Nanotechnology plays a critical role in the structural modification of photosynthetic protein complexes to improve light energy conversion efficiency. For instance, the integration of photosynthetic membrane proteins with mesoporous WO3 photoelectrodes has led to significant enhancements in photocurrent generation and quantum efficiency (Pang et al., 2018). Similarly, the use of dual-emissive carbon dots to coat chloroplasts has resulted in a substantial increase in adenosine triphosphate (ATP) production, demonstrating the potential of nanotechnology to augment photosynthetic processes both in vitro and in vivo (Li et al., 2018). Furthermore, the development of artificial nanoscale devices that mimic natural photosynthetic systems has been made possible through advances in chemical synthesis and instrumentation, allowing for the creation of artificial light-harvesting antennas and reaction centers (Gust et al., 2001).

6.3 Application of CRISPR/Cas9 for targeted genetic modifications

The application of CRISPR/Cas9 technology for targeted genetic modifications has opened new possibilities for optimizing photosynthetic efficiency. This gene-editing tool allows for precise modifications of photosynthetic organisms, enabling the enhancement of light-harvesting capabilities and the optimization of energy conversion pathways. For example, CRISPR/Cas9 can be used to introduce foreign electron-exporting conduits into photosynthetic bacteria, thereby improving their electron transport capabilities and overall solar conversion efficiency (Schuergers et al., 2017). Additionally, targeted genetic modifications can be employed to fine-tune the structural and functional hierarchy of photosynthetic complexes, ensuring efficient energy transfer and charge separation (Szabó et al., 2015). This approach not only enhances the fundamental understanding of photosynthetic mechanisms but also provides a basis for the rational redesign of photosynthetic systems for improved performance.

By leveraging these innovative approaches and emerging technologies, researchers are making significant strides in optimizing photosynthetic protein complex structures to improve light energy conversion efficiency. The integration of synthetic biology, nanotechnology, and CRISPR/Cas9 offers a multifaceted strategy to address the challenges and unlock the full potential of artificial photosynthetic systems.

7 Potential Applications and Implications

7.1 Agricultural improvements: enhancing crop yield and resilience

Optimizing photosynthetic protein complex structures holds significant promise for agricultural advancements. By improving the efficiency of photosynthesis, we can potentially increase the yield potential of major crops. Enhancements in light interception, energy transduction, and carbohydrate synthesis can lead to more productive germplasm, which is crucial for meeting the rising global food demand (Zhu et al., 2010; Garcia et al., 2022). Techniques such as classical breeding, systems biology, and synthetic biology are being explored to develop crops with better leaf display and photorespiratory bypasses, which have already shown productivity improvements in model species (Zhu et al., 2010). Additionally, engineering plants with carboxylases better adapted to current and future CO₂ concentrations can further maximize carbon gain without increasing crop inputs, potentially doubling the yield potential of major crops (Zhu et al., 2010).

7.2 Renewable energy production: development of biohybrid and artificial photosynthetic systems

The development of biohybrid and artificial photosynthetic systems is a promising avenue for renewable energy production. Photosynthetic proteins, with their near-perfect quantum efficiency, are being integrated into photovoltaic devices to create biohybrid solar cells that promise better efficiency than conventional solar cells (Ravi and Tan, 2015). These systems combine the natural light-harvesting capabilities of photosynthetic proteins with engineered materials to enhance photocurrent generation and stability (Ravi and Tan, 2015). Furthermore, artificial photosynthetic systems are being designed to mimic natural photosynthesis, using semiconductors and biomimetic complexes to harvest light, separate charges, and catalyze redox reactions for solar fuel production (Wasielewski, 2009; Wen and Li, 2013). These advancements could lead to the development of efficient and stable systems for converting solar energy into chemical fuels, addressing global energy challenges (Wen and Li, 2013; Cestellos-Blanco et al., 2020).

7.3 Environmental benefits: carbon sequestration and ecosystem restoration

Optimizing photosynthetic protein complexes can also have significant environmental benefits, particularly in carbon sequestration and ecosystem restoration. Enhanced photosynthetic efficiency can increase the rate of CO₂ fixation, contributing to the reduction of atmospheric CO₂ levels and mitigating climate change (Mussgnug et al., 2007; Cestellos-Blanco et al., 2020). Photosynthetic semiconductor biohybrids, for instance, are being developed to convert CO₂ into value-added chemicals, providing a sustainable approach to carbon management (Cestellos-Blanco et al., 2020). Additionally, bioinspired systems that mimic natural photosynthesis can be used to restore ecosystems by improving the growth and resilience of plants in degraded environments (Proppe et al., 2020). These systems can enhance the efficiency of light harvesting and catalysis, facilitating the conversion of solar energy into biomass and supporting ecosystem restoration efforts (Proppe et al., 2020).

By leveraging the advancements in photosynthetic protein complex optimization, we can achieve significant improvements in agriculture, renewable energy production, and environmental sustainability, addressing some of the most pressing challenges of our time.

8 Future Directions and Research Needs

8.1 Identifying key areas for future research

To further optimize photosynthetic protein complex structures for improved light energy conversion efficiency, several key areas require focused research. One critical area is the development of self-assembling and self-ordering components that can mimic the natural organization of photofunctional chromophores and catalysts within proteins. This approach could enhance the efficiency of artificial photosynthetic systems by providing tailored environments for chemical reactions, similar to those found in natural photosynthesis (Wasielewski, 2009). Additionally, understanding the structural and functional variability of photosystem complexes across different organisms can provide insights into optimizing light-harvesting efficiency under various environmental conditions (Croce and Amerongen, 2020). Research should also focus on the integration of photosynthetic protein complexes into solid-state devices to achieve higher internal quantum efficiencies and practical applications in photovoltaic cells (Das et al., 2004; Kamran et al., 2014).

8.2 Integrating multidisciplinary approaches for comprehensive optimization

A multidisciplinary approach is essential for the comprehensive optimization of photosynthetic protein complexes. Combining structural biology, advanced spectroscopy, and computational modeling can provide a detailed understanding of energy transfer pathways and bottlenecks in photosynthetic systems (Croce and Amerongen, 2020). Techniques such as cryo-electron microscopy and X-ray scattering can elucidate the three-dimensional structures of photosystem complexes, revealing the interactions between protein subunits and pigments at atomic resolution (Jordan et al., 2001; Su et al., 2017). Additionally, incorporating principles from quantum mechanics can help explain the long-range coherence observed in light-harvesting proteins, potentially leading to more efficient energy transfer mechanisms (Collini et al., 2010). Collaboration between biologists, chemists, physicists, and engineers will be crucial to translate these fundamental insights into practical applications.

8.3 Addressing challenges in scalability and practical implementation

Scalability and practical implementation of optimized photosynthetic protein complexes pose significant challenges. One major hurdle is the efficient integration of these complexes into large-scale devices while maintaining their structural integrity and functional efficiency. Techniques such as the Langmuir-Blodgett method for creating densely packed monolayers of protein complexes on electrodes show promise but require further refinement to enhance electronic contact and alignment (Kamran et al., 2014). Additionally, addressing the overpotential and stability issues associated with water oxidation in photosystem II is critical for developing efficient solar fuel production technologies (Dau and Zaharieva, 2009). Research should also focus on genetic and biochemical strategies to reduce energy losses due to fluorescence and heat in photosynthetic organisms, thereby improving the overall efficiency of biofuel production under high-light conditions (Mussgnug et al., 2007). Overcoming these challenges will require innovative engineering solutions and continued interdisciplinary collaboration.

9 Concluding Remarks

The optimization of photosynthetic protein complex structures has shown significant potential in improving light energy conversion efficiency. Key findings from various studies highlight the importance of structural organization and the integration of light-harvesting and charge separation mechanisms. For instance, self-assembly strategies involving pi-stacking have been explored to integrate light harvesting with charge separation and transport, utilizing robust arylene imide and diimide dyes, biomimetic porphyrins, and chlorophylls to form supramolecular structures with enhanced energy capture and charge-transport properties. Additionally, the structural diversity of Photosystem I (PSI) and its light-harvesting complexes (LHCI) in eukaryotic algae and plants has been shown to play a crucial role in achieving high quantum efficiency, with recent studies revealing the detailed arrangement of pigments and cofactors that facilitate efficient energy transfer.

Moreover, advancements in intracellular spectral recompositioning (ISR) of light have demonstrated a 28% increase in photosynthetic efficiency in engineered diatoms, highlighting the potential of spectral conversion to enhance light utilization. The development of hybrid reaction centers, such as the RC/YFP complex, has also been shown to augment energy transfer and trapping in photosynthesis by increasing spectral coverage. Furthermore, the use of bio-dyes from photosynthetic macromolecules on designed TiO2 films has led to significant improvements in the performance of bio-dye sensitized solar cells, showcasing the potential for better utilization of solar energy.

The optimization of photosynthetic protein complexes holds immense promise for enhancing light energy conversion efficiency. The integration of advanced structural and spectroscopic techniques has provided deeper insights into the mechanisms of energy transfer and charge separation, paving the way for the development of more efficient artificial photosynthetic systems. The ability to manipulate and optimize the spatial arrangement of protein subunits and binding cofactors, as seen in the PSI-LHCI supercomplexes, is crucial for achieving near-perfect quantum efficiency.

Furthermore, the incorporation of non-native light-absorbers and the use of self-assembling biohybrid systems offer innovative approaches to extend the spectral range and improve the overall efficiency of light capture and conversion. These advancements not only enhance our understanding of natural photosynthesis but also provide a foundation for the rational design of artificial photochemical devices and bio-photovoltaic systems. As research continues to uncover the intricate details of photosynthetic protein complexes, the potential for significant improvements in solar energy conversion and sustainable energy production becomes increasingly attainable.

Acknowledgments

The BioSci Publisher appreciate the feedback from two anonymous peer reviewers on the manuscript of this study, whose careful evaluation and constructive suggestions have contributed to the improvement of the manuscript.

Conflict of Interest Disclosure

The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

References

Allouche D., André I., Barbe S., Davies J., Givry S., Katsirelos G., O’Sullivan B., Prestwich S., Schiex T., and Traoré S., 2014, Computational protein design as an optimization problem, Artif. Intell., 212: 59-79.

https://doi.org/10.1016/j.artint.2014.03.005

Amunts A., and Nelson N., 2009, Plant photosystem I design in the light of evolution, Structure, 17(5): 637-650.

https://doi.org/10.1016/j.str.2009.03.006

Bai T., Guo L., Xu M., and Tian L., 2021, Structural diversity of photosystem i and its light-harvesting system in eukaryotic algae and plants, Frontiers in Plant Science, 12.

https://doi.org/10.3389/fpls.2021.781035

Batista-Silva W., Fonseca-Pereira P., Martins A., Zsögön A., Nunes-Nesi A., and Araújo W., 2020, Engineering improved photosynthesis in the era of synthetic biology, Plant Communications, 1(2): 100032.

https://doi.org/10.1016/j.xplc.2020.100032

Bennett D., Amarnath K., and Fleming G., 2013, A structure-based model of energy transfer reveals the principles of light harvesting in photosystem II supercomplexes, Journal of the American Chemical Society, 135(24): 9164-9173.

https://doi.org/10.1021/ja403685a

Brown K., and King P., 2019, Coupling biology to synthetic nanomaterials for semi-artificial photosynthesis, Photosynthesis Research, 143: 193-203.

https://doi.org/10.1007/s11120-019-00670-5

Cestellos-Blanco S., Zhang H., Kim J., Shen Y., and Yang P., 2020, Photosynthetic semiconductor biohybrids for solar-driven biocatalysis, Nature Catalysis, 3: 245-255.

https://doi.org/10.1038/s41929-020-0428-y

Chukhutsina V., Bersanini L., Aro E., and Amerongen H., 2015, Cyanobacterial flv4-2 operon-encoded proteins optimize light harvesting and charge separation in photosystem II, Molecular plant, 8(5): 747-761.

https://doi.org/10.1016/j.molp.2014.12.016

Collini E., Wong C., Wilk K., Curmi P., Brumer P., and Scholes G., 2010, Coherently wired light-harvesting in photosynthetic marine algae at ambient temperature, Nature, 463: 644-647.

https://doi.org/10.1038/nature08811

Crepin A., Kučerová Z., Kosta A., Durand E., and Caffarri S., 2019, Isolation and characterization of a large Photosystem I-Light Harvesting complex II supercomplex with an additional Lhca1-a4 dimer in Arabidopsis, The Plant Journal : for Cell and Molecular Biology, 102(2): 398-409.

https://doi.org/10.1111/tpj.14634

Croce R., and Amerongen H., 2011, Light-harvesting and structural organization of Photosystem II: from individual complexes to thylakoid membrane, Journal of Photochemistry and Photobiology. B, Biology, 104(1-2): 142-153.

https://doi.org/10.1016/j.jphotobiol.2011.02.015

Croce R., and Amerongen H., 2020, Light harvesting in oxygenic photosynthesis: Structural biology meets spectroscopy, Science, 369(6506): eaay2058.

https://doi.org/10.1126/science.aay2058

Das R., Kiley P., Segal M., Norville J., Yu A., Wang L., Trammell S., Reddick L., Kumar R., Stellacci F., Lebedev N., Schnur J., Bruce B., Zhang S., and Baldo M., 2004, Integration of Photosynthetic Protein Molecular Complexes in Solid-State Electronic Devices, Nano Letters, 4: 1079-1083.

https://doi.org/10.1021/NL049579F

Dau H., and Zaharieva I., 2009, Principles, efficiency, and blueprint character of solar-energy conversion in photosynthetic water oxidation, Accounts of Chemical Research, 42(12): 1861-1870.

https://doi.org/10.1021/ar900225y

Galka P., Santabarbara S., Khuong T.T.H., Degand H., Morsomme P., Jennings R.C., Boekema E.J., and Caffarria S., 2012, Functional analyses of the plant photosystem I-light-harvesting complex II supercomplex reveal that light-harvesting complex II loosely bound to photosystem ii is a very efficient antenna for photosystem I in state II, Plant Cell, 24: 2963-2978.

Garcia A., Gaju O., Bowerman A., Buck S., Evans J., Furbank R., Gilliham M., Millar A., Pogson B., Reynolds M., Ruan Y., Taylor N., Tyerman S., and Atkin O., 2022, Enhancing crop yields through improvements in the efficiency of photosynthesis and respiration, The New Phytologist, 237: 60-77.

https://doi.org/10.1111/nph.18545

Gust D., Moore T., and Moore A., 2001, Mimicking photosynthetic solar energy transduction, Accounts of Chemical Research, 34(1): 40-48.

https://doi.org/10.1021/AR9801301

Harrison M., and Allen J., 1992, Protein phosphorylation and Mg2+ influence light harvesting and electron transport in chloroplast thylakoid membrane material containing only the chlorophyll-a/b-binding light-harvesting complex of photosystem II and photosystem I, European Journal of Biochemistry, 204(3): 1107-1114.

https://doi.org/10.1111/J.1432-1033.1992.TB16735.X

Hsieh S., Zhang L., Ye D., Huang X., and Cheng Y., 2019, A theoretical study on the dynamics of light harvesting in the dimeric photosystem II core complex: regulation and robustness of energy transfer pathways, Faraday Discussions, 216: 94-115.

https://doi.org/10.1039/C8FD00205C

Jordan P., Fromme P., Witt H., Klukas O., Saenger W., and Krauß N., 2001, Three-dimensional structure of cyanobacterial photosystem I at 2.5 Å resolution. Nature, 411: 909-917.

https://doi.org/10.1038/35082000

Kamran M., Delgado J., Friebe V., Aartsma T., and Frese R., 2014, Photosynthetic protein complexes as bio-photovoltaic building blocks retaining a high internal quantum efficiency.. Biomacromolecules, 15(8): 2833-2838.

https://doi.org/10.1021/bm500585s

Kim Y., Morozov D., Stadnytskyi V., Savikhin S., and Slipchenko L., 2020, Predictive first-principles modeling of a photosynthetic antenna protein: the fenna-matthews-olson complex, The Journal of Physical Chemistry Letters, 11(5): 1636-1643.

https://doi.org/10.1021/acs.jpclett.9b03486

Kouřil R., Zygadlo A., Arteni A.A., de Wit C.D., Dekker J.P., Jensen P.E., Scheller H.V., and Boekema E.J., 2005, Structural characterization of a complex of photosystem I and light-harvesting complex II of Arabidopsis thaliana. Biochemistry, 44: 10935-10940.

Li W., Wu S., Zhang H., Zhang X., Zhuang J., Hu C., Liu Y., Lei B., Ma L., and Wang X., 2018, Enhanced biological photosynthetic efficiency using light-harvesting engineering with dual-emissive carbon dots, Advanced Functional Materials, 28(44): 1804004.

https://doi.org/10.1002/adfm.201804004

Liu J., Friebe V., Frese R., and Jones M., 2019, Polychromatic solar energy conversion in pigment-protein chimeras that unite the two kingdoms of (bacterio)chlorophyll-based photosynthesis, Nature Communications, 11(1): 1542.

https://doi.org/10.1038/s41467-020-15321-w

Liu J., Mantell J., and Jones M., 2020, Minding the gap between plant and bacterial photosynthesis within a self-assembling biohybrid photosystem, ACS nano, 14(4): 4536-4549.

https://doi.org/10.1021/acsnano.0c00058

Mulfort K., and Utschig L., 2016, Modular homogeneous chromophore-catalyst assemblies, Accounts of Chemical Research, 49(5): 835-843.

https://doi.org/10.1021/acs.accounts.5b00539

Mussgnug J., Thomas-Hall S., Rupprecht J., Foo A., Klassen V., McDowall A., Schenk P., Kruse O., and Hankamer B., 2007, Engineering photosynthetic light capture: impacts on improved solar energy to biomass conversion, Plant Biotechnology Journal, 5(6):802-814.

https://doi.org/10.1111/J.1467-7652.2007.00285.X

Nelson N., and Junge W., 2015, Structure and energy transfer in photosystems of oxygenic photosynthesis, Annual Review of Biochemistry, 84: 659-683.

https://doi.org/10.1146/annurev-biochem-092914-041942

Nelson N., and Yocum C., 2006, Structure and function of photosystems I and II, Annual Review of Plant Biology, 57: 521-565.

https://doi.org/10.1146/ANNUREV.ARPLANT.57.032905.105350

Pachon L., and Brumer P., 2012, Computational methodologies and physical insights into electronic energy transfer in photosynthetic light-harvesting complexes, Physical chemistry chemical physics: PCCP, 14(29): 10094-10108.

https://doi.org/10.1039/c2cp40815e

Pan X., Cao P., Su X., Liu Z., and Li M., 2020, Structural analysis and comparison of light-harvesting complexes I and II, Biochimica et biophysica acta, Bioenergetics, 1861(4): 148038.

https://doi.org/10.1016/j.bbabio.2019.06.010

Pan X., Ma J., Su X., Cao P., Chang W., Liu Z., Zhang X., and Li M., 2018, Structure of the maize photosystem I supercomplex with light-harvesting complexes I and II. Science, 360: 1109-1113.

Pang H., Zhao G., Liu G., Zhang H., Hai X., Wang S., Song H., and Ye J., 2018, Interfacing photosynthetic membrane protein with mesoporous WO3 photoelectrode for solar water oxidation, Small, 14(19): e1800104.

https://doi.org/10.1002/smll.201800104

Proppe A., Li Y., Aspuru-Guzik A., Berlinguette C., Chang C., Cogdell R., Doyle A., Flick J., Gabor N., Grondelle R., Hammes‐Schiffer S., Jaffer S., Kelley S., Leclerc M., Leo K., Mallouk T., Narang P., Schlau-Cohen G., Scholes G., Vojvodić A., Yam V., Yang J., and Sargent E., 2020, Bioinspiration in light harvesting and catalysis, Nature Reviews Materials, 5: 828-846.

https://doi.org/10.1038/s41578-020-0222-0

Qin X., Suga M., Kuang T., and Shen J., 2015, Structural basis for energy transfer pathways in the plant PSI-LHCI supercomplex, Science, 348: 989-995.

https://doi.org/10.1126/science.aab0214

Ravi S., and Tan S., 2015. Progress and perspectives in exploiting photosynthetic biomolecules for solar energy harnessing, Energy and Environmental Science, 8: 2551-2573.

https://doi.org/10.1039/C5EE01361E

Schuergers N., Werlang C., Ajo-Franklin C., and Boghossian A., 2017, A synthetic biology approach to engineering living photovoltaics, Energy and Environmental Science, 10(5): 1102-1115.

https://doi.org/10.1039/C7EE00282C

Shang H., Li M., and Pan X., 2023, Dynamic regulation of the light-harvesting system through state transitions in land plants and green algae, Plants, 12(5): 1173.

https://doi.org/10.3390/plants12051173

Sirohiwal A., Neese F., and Pantazis D., 2021, Chlorophyll excitation energies and structural stability of the CP47 antenna of photosystem II: a case study in the first-principles simulation of light-harvesting complexes, Chemical Science, 12: 4463-4476.

https://doi.org/10.1039/D0SC06616H

Stieger K., Ciornii D., Kölsch A., Hejazi M., Lokstein H., Feifel S., Zouni A., and Lisdat F., 2016, Engineering of supramolecular photoactive protein architectures: the defined co-assembly of photosystem I and cytochrome c using a nanoscaled DNA-matrix, Nanoscale, 8(20): 10695-10705.

https://doi.org/10.1039/c6nr00097e

Su X., Ma J., Wei X., Cao P., Zhu D., Chang W., Liu Z., Zhang X., and Li M., 2017, Structure and assembly mechanism of plant C2S2M2-type PSII-LHCII supercomplex, Science, 357: 815-820.

https://doi.org/10.1126/science.aan0327

Suga M., Akita F., Hirata K., Ueno G., Murakami H., Nakajima Y., Shimizu T., Yamashita K., Yamamoto M., Ago H., and Shen J., 2014, Native structure of photosystem II at 1.95 Å resolution viewed by femtosecond X-ray pulses, Nature, 517: 99-103.

https://doi.org/10.1038/nature13991.

Suga M., Ozawa S.I., Yoshida-Motomura K., Akita F., Miyazaki N., and Takahashi Y., 2019, Structure of the green algal photosystem I supercomplex with a decameric light-harvesting complex I, Nat. Plants, 5: 626-636.

Szabó T., Magyar M., Hajdu K., Dorogi M., Nyerki E., Tóth T., Lingvay M., Garab G., Hernádi K., and Nagy L., 2015, Structural and functional hierarchy in photosynthetic energy conversion—from molecules to nanostructures, Nanoscale Research Letters, 10: 1-12.

https://doi.org/10.1186/s11671-015-1173-z

Wasielewski M., 2009, Self-assembly strategies for integrating light harvesting and charge separation in artificial photosynthetic systems, Accounts of Chemical Research, 42(12): 1910-1921.

https://doi.org/10.1021/ar9001735

Wen F., and Li C., 2013, Hybrid artificial photosynthetic systems comprising semiconductors as light harvesters and biomimetic complexes as molecular cocatalysts, Accounts of Chemical Research, 46(11): 2355-2364.

https://doi.org/10.1021/ar300224u

Yadav K., Semchonok D., Nosek L., Kouřil R., Fucile G., Boekema E., and Eichacker L., 2017, Supercomplexes of plant photosystem I with cytochrome b6f, light-harvesting complex II and NDH, Biochimica et biophysica acta, Bioenergetics, 1858(1): 12-20.

https://doi.org/10.1016/j.bbabio.2016.10.006

Zhu X., Long S., and Ort D., 2010, Improving photosynthetic efficiency for greater yield, Annual Review of Plant Biology, 61: 235-261.

https://doi.org/10.1146/annurev-arplant-042809-112206