Characterization of SyrC, an aminoacyltransferase shuttling threonyl and chlorothreonyl residues in the syringomycin biosynthetic assembly line |
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Authors: | Singh Gitanjali M Vaillancourt Frédéric H Yin Jun Walsh Christopher T |
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Institution: | Department of Biological Chemistry & Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA. |
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Abstract: | Syringomycin, a lipopeptidolactone assembled from nine amino acid monomers by four enzymes, SyrB1, SyrB2, SyrC, and SyrE, is a cyclic nonribosomal peptide made by plant-associated Pseudomonas spp. This assembly is unusual because the terminal residue, 4-chlorothreonine, has been proposed to be added in trans since the ninth module of the megasynthetase SyrE lacks an adenylation domain required for Thr/Cl-Thr activation. SyrC is now identified as a Thr/Cl-Thr aminoacyltransferase, shuttling the Thr/Cl-Thr moiety between the pantetheinyl arms of the thiolation domain of SyrB1 and the thiolation domain in module nine of SyrE. SyrC uses Cys224 as a catalytic nucleophile to generate a Thr/Cl-Thr-S-enzyme intermediate during transfer. SyrC joins a growing family of such aminoacyl-shuttling enzymes that also use covalent catalysis to move aminoacyl groups from carrier proteins during coumermycin and coronamic acid biosynthesis. |
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