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. PTM introduces structural changes such as the addition of chemical groups or carbohydrate chains to the individual amino acids that make up proteins. This results in hundreds of possible variations for the same protein chain.
These variants play pivotal roles in biology, by enabling precise regulation of complex biological processes within individual cells. Mapping this variation would uncover a wealth of valuable information that could revolutionise our understanding of cellular functions. 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-based sensing 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.