Biosynthesis of the β-Methylarginine Residue of Peptidyl Nucleoside Arginomycin in Streptomyces arginensis NRRL 15941

Abstract

ABSTRACT The peptidyl nucleoside arginomycin is active against Gram-positive bacteria and fungi but displays much lower toxicity to mice than its analog blasticidin S. It features a rare amino acid, β-methylarginine, which is attached to the deoxyhexose moiety via a 4′-aminoacyl bond. We here report cloning of the complete biosynthetic gene cluster for arginomycin from Streptomyces arginensis NRRL 15941. Among the 14 putative essential open reading frames, argM , encoding an aspartate aminotransferase (AAT), and adjacent argN , encoding an S -adenosyl methionine (SAM)-dependent methyltransferase, are coupled to catalyze arginine and yield β-methylarginine in Escherichia coli . Purified ArgM can transfer the α-amino group of l -arginine to α-ketoglutaric acid to give glutamate and thereby converts l -arginine to 5-guanidino-2-oxopentanoic acid, which is methylated at the C-3 position by ArgN to form 5-guanidino-3-methyl-2-oxopentanoic acid. Iteratively, ArgM specifically catalyzes transamination from the donor l -aspartate to the resulting 5-guanidino-3-methyl-2-oxopentanoic acid, generating β-methylarginine. The complete and concise biosynthetic pathway for the rare and bioactive amino acid revealed by this study may pave the way for the production of β-methylarginine either by enzymatic conversion or by engineered living cells.