An Atypical Arginine Dihydrolase Involved in the Biosynthesis of Cyclic Hexapeptide Longicatenamides

Abstract

The incorporation of non‐proteinogenic amino acids (NPAAs) enriches the structural diversity of nonribosomal peptides. Recently, four NPAA‐containing cyclic hexapeptides, longicatenamides A−D, were isolated using a combined‐culture strategy. Based on in silico analysis, we discovered their putative biosynthetic gene cluster (lon) and proposed a possible biosynthetic mechanism. Surprisingly, the lon22 gene encodes an atypical arginine dihydrolase, which can also catalyze the hydrolysis of citrulline to ornithine. Phylogenetic analysis showed that Lon22‐like proteins form a novel clade that is separated from other guanidine‐modifying enzymes. After rational design, the catalytic efficiencies of a Lon22 Y80F mutant for arginine and citrulline substrates were 2.31‐ and 4.70‐fold that of the wild‐type (WT), respectively. In addition, characterization of the Lon20‐A4 adenylation domain suggested that it can incorporate both ornithine and lysine into the final products.

Streamlined Chemoenzymatic Synthesis of Cyclic Peptides by Non-ribosomal Peptide Cyclases

“…Their cyclic scaffolds, typically ranging from 4 to 15 residues, are constructed by several distinct groups of NRP cyclases, and penicillin-binding protein-type thioesterases (PBP-type TEs) are an emerging group of stand-alone NRP cyclases (Figure S1). − Among them, SurE cyclase in the surugamide biosynthetic pathway from several Streptomyces spp. is particularly interesting from a biocatalytic perspective, owing to its inherent substrate tolerance: it cyclizes structurally distinct substrates to biosynthesize two groups of non-ribosomal macrolactams in vivo (Figure S2).…”