Investigation of Indigoidine Synthetase Reveals a Conserved Active-Site Base Residue of Nonribosomal Peptide Synthetase Oxidases
Bo Pang, Yan Chen, Fei Gan, Chunsheng Yan, Liyuan Jin, Jennifer Gin, Christopher J. Petzold, Jay D. Keasling
Abstract
Nonribosomal peptide synthetase (NRPS) oxidase (Ox) domains oxidize protein-bound intermediates to install crucial structural motifs in bioactive natural products. The mechanism of this domain remains elusive. Here, by studying indigoidine synthetase, a single-module NRPS involved in the biosynthesis of indigoidine and several other bacterial secondary metabolites, we demonstrate that its Ox domain utilizes an active-site base residue, tyrosine 665, to deprotonate a protein-bound l-glutaminyl residue. We further validate the generality of this active-site residue among NRPS Ox domains. These findings not only resolve the biosynthetic pathway mediated by indigoidine synthetase but enable mechanistic insight into NRPS Ox domains.