Custom Proteins Clarify Splicing Mechanism

Proteins that splice themselves get a jump start from a special branched conformation, a structural and biochemical research study suggests (Nat. Chem. Biol., DOI: 10.1038/nchembio.371). Protein splicing is a posttranslational process in which a peptide sequence called an intein excises itself from a host protein called the extein. It happens in a variety of single-cell life forms. Researchers have previously studied such splicing with inactivated mutant proteins, but the current mechanistic picture is incomplete. To learn more, Tom W. Muir of Rockefeller University, David Cowburn of the New York Structural Biology Center, and coworkers generated custom-made, fully active proteins. The proteins’ natural splicing process proceeds through a branched peptide intermediate. The team found that the release of the intein—the splicing reaction’s rate-limiting step—is slower in unbranched peptides. The team’s NMR studies suggest that branching distorts the peptide into more reactive conformations, facilitating formation of the correct intein product. That knowledge could help researchers design better inteins for chemical biology, Muir says, because in vitro inteins tend to undergo more side reactions than their counterparts in living organisms.