Human cells contain approximately 20,000 protein-encoding genes. However, the actual number of proteins observed in cells is far greater, with over 1,000,000 different structures known. These variants are generated through a process known as post-translational modification (PTM), which occurs after a protein has been transcribed from DNA. But to date, the ability to produce comprehensive protein inventories has remained an elusive goal. To overcome this, a team led by researchers at the University of Oxford's Department of Chemistry has successfully developed a method for protein analysis based on nanopore DNA/RNA sequencing technology.

 

In this approach, a directional flow of water captures and unfolds 3D proteins into linear chains that are fed through tiny pores, just wide enough for a single amino acid molecule to pass through. Structural variations are identified by measuring changes in an electrical current applied across the nanopore. Different molecules cause different disruptions in the current, giving them a unique signature. The team successfully demonstrated the method's effectiveness in detecting three different PTM modifications (phosphorylation, glutathionylation, and glycosylation) at the single-molecule level for protein chains over 1 200 residues long. These included modifications deep within the protein's sequence.