The rate-limiting step of protein splicing ― a type of protein modification post translation ― and the trigger that catalyzes this reaction are identified in a study published online this week in Nature Chemical Biology.
During protein splicing an intein ― a short protein sequence ― spontaneously extracts itself from the host protein. Previous studies have identified four steps in this process, but were also forced to use inactivated, mutant proteins to study the process.
Tom Muir and colleagues now use nuclear magnetic resonance as well as traditional enzyme assays to study tailor-made proteins that are still active. This allowed the researchers to pinpoint the rate-limiting step in protein splicing as the third step in the sequence. A particular arrangement of the protein structure is also found to jump-start this transformation. These discoveries help to clarify why protein splicing does not occur more often or by accident.