Characterization of Enzymes Catalyzing the Initial Steps of the β-Lactam Tabtoxin Biosynthesis.

Tabtoxin is a β-lactam ring-containing phytotoxin produced by a plant pathogenic species. Here, we describe the early stages of tabtoxin biosynthesis, involving a -methylation reaction catalyzed by the -adenosyl-l-methionine-dependent methyltransferase TblA as the initial step for the β-lactam construction. Gene deletion and biochemical assays demonstrated that the Gcn5-related -acetyltransferase domain of TblD catalyzes the acetylation of the α-amino group of 5-methyl-l-lysine. This establishment of the early reaction steps lays the foundation for characterizing unique β-lactam biosynthesis.