4-Nitrotryptophan is a substrate for the non-ribosomal peptide synthetase TxtB in the thaxtomin A biosynthetic pathway

• Published in: Molecular microbiology 2009-08, Vol.73 (3), p.409-418
• Main Authors: Johnson, Evan G, Krasnoff, Stuart B, Bignell, Dawn R.D, Chung, Wen-Chuan, Tao, Tao, Parry, Ronald J, Loria, Rosemary, Gibson, Donna M
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biological and medical sciences; Cellulose; Enzymes; Fundamental and applied biological sciences. Psychology; Indoles - metabolism; Microbiology; Mutation; Peptide Synthases - genetics; Peptide Synthases - metabolism; Peptides; Piperazines - metabolism; Protein synthesis; RNA, Bacterial - genetics; Streptomyces; Streptomyces - genetics; Streptomyces - metabolism; Substrate Specificity; Tryptophan - analogs & derivatives; Tryptophan - metabolism
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2009.06780.x

Thaxtomin A, a cyclic dipeptide with a nitrated tryptophan moiety, is a phytotoxic pathogenicity determinant in scab-causing Streptomyces species that inhibits cellulose synthesis by an unknown mechanism. Thaxtomin A is produced by the action of two non-ribosomal peptide synthetase modules (TxtA and TxtB) and a complement of modifying enzymes, although the order of biosynthesis has not yet been determined. Analysis of a thaxtomin dual module knockout mutant and single module knockout mutants revealed that 4-nitrotryptophan is an intermediate in thaxtomin A biosynthesis prior to backbone assembly. The 4-nitrotryptophan represents a novel substrate for non-ribosomal peptide synthetases. Through identification of N-methyl-4-nitrotryptophan in a single module knockout and the use of adenylation domain specificity prediction software, TxtB was identified as the non-ribosomal peptide synthetase module specific for 4-nitrotryptophan.