Structural analysis of leader peptide binding enables leader-free cyanobactin processing

Regioselective modification of amino acids within the context of a peptide is common to a number of biosynthetic pathways and many such products have potential as therapeutics. The ATP dependent enzyme LynD heterocyclizes multiple cysteine residues to thiazolines within a peptide substrate. The enzyme requires the substrate to have conserved N-terminal leader for full activity. Catalysis is almost insensitive to immediately flanking residues in the substrate suggesting recognition occurs distant from the active site. Nucleotide and peptide substrate co-complex structures of LynD reveal the substrate leader peptide binds to and extends the β-sheet of a conserved domain of LynD, whilst catalysis is accomplished in another conserved domain. The spatial segregation of catalysis from recognition combines seemingly contradictory properties of regioselectivity and promiscuity; it appears to be a conserved strategy in other peptide modifying enzymes. A variant of LynD that efficiently processes substrates without a leader peptide has been engineered.