Expression and characterization of Rv0447c product, potentially the methyltransferase involved in tuberculostearic acid biosynthesis in Mycobacterium tuberculosis

Abstract

In this study, a previously uncharacterized gene (Rv0447c) of Mycobacterium tuberculosis, designated as an unknown fatty-acid methyltransferase (ufaA1), was cloned, expressed in Escherichia coli, and purified. The biochemical characterization of the purified protein (UfaA1) showed it to be a methyltransferase that catalyzes biosynthesis of the tuberculostearic acid (10-methylstearic-acid, TSA), a significant constituent lipid of the mycobacterial cell wall and a clinical marker of the disease. Here, we show that UfaA1 transfers the methyl group from S-adenosyl-l-methionine (SAM) to the double bond of oleic acid in phosphatidylethanolamine or phosphatidylcholine to produce TSA. Optimal activity was obtained between pH 7.0 and pH 8.0. The methyltransferase activity of UfaA1 was severely inhibited by S-adenosyl-l-homocysteine. The Km values for dioleyl phosphatidylethanolamine, SAM, and nicotinamide adenine dinucleotide phosphate were 14, 13, and 83 µM, respectively, with Vmax of 1.3-1.6 nmol/Min. These results identify the Rv0447c gene product of M. tuberculosis as the methyltransferase that catalyzes the biosynthesis of TSA. This provides new information in mycobacterial cell wall synthesis.

Keywords: Mycobacterium tuberculosis; S-adenosyl-l-methionine; fatty-acid; methyltransferase; oleic-acid; tuberculostearic acid.