Evidence for C-Methylation Proceeding via a Cyclopropane Intermediate during Tabtoxin Biosynthesis

Area of Science:

• Biochemistry
• Natural Product Biosynthesis
• Enzymology

Background:

• Genomic era natural product discovery necessitates enzyme function validation.
• Tabtoxin biosynthesis involves complex pathways for antimicrobial and herbicidal compounds.

Purpose of the Study:

• Elucidate the biosynthetic logic of a rare C-methylation at the C5-position of lysine in tabtoxin.
• Identify novel enzymes and pathways involved in tabtoxin precursor synthesis.

Main Methods:

• Enzyme characterization of novel SAM-dependent cyclopropane synthase (TblA) and dual function cyclopropane hydrolase/N-acyltransferase (TabB).
• Analysis of metabolic branching via TabD-catalyzed transamination on l-2,3,4,5-tetrahydro-dipicolinic acid (THDPA).

Main Results:

• Established a novel biosynthetic pathway for C5-methylation involving cyclopropane ring formation and hydrolysis.
• Identified TblA as a SAM-dependent cyclopropane synthase and TabB as a dual function enzyme.
• Discovered a new metabolic branch of lysine biosynthesis providing direct access to meso-diaminopimelate via THDPA.

Conclusions:

• The study elucidates the mechanistic basis and enzyme order for C1-unit incorporation in tabtoxin biosynthesis.
• Findings explain the construction of monobactams in the tabtoxin family, expanding knowledge of natural product synthesis.