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Identification of a Novel Galactosyl Transferase Involved in Biosynthesis of the Mycobacterial Cell Wall

Katarína Mikuová,¹ Martina Beláová,¹ Jana Korduláková,¹ Kristine Honda,² Michael R. McNeil,² Sebabrata Mahapatra,² Dean C. Crick,² and Patrick J. Brennan^2*

Department of Biochemistry, Comenius University, Faculty of Natural Sciences, Bratislava, Slovakia, SK-842 15,¹ Mycobacterial Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado 80523²

Received 6 April 2006/ Accepted 15 June 2006

The possibility of the Rv3782 protein of Mycobacterium tuberculosis being a putative galactosyl transferase (GalTr) implicated in galactan synthesis arose from its similarity to the known GalTr Rv3808c, its classification as a nucleotide sugar-requiring inverting glycosyltransferase (GT-2 family), and its location within the "possible arabinogalactan biosynthetic gene cluster" of M. tuberculosis. In order to study the function of the enzyme, active membrane and cell wall fractions from Mycobacterium smegmatis containing the overexpressed Rv3782 protein were incubated with endogenous decaprenyldiphosphoryl-N-acetylglucosaminyl-rhamnose (C₅₀-P-P-GlcNAc-Rha) as the primary substrate for galactan synthesis and UDP-[¹⁴C]galactopyranose as the immediate precursor of UDP-[¹⁴C]galactofuranose, the ultimate source of all of the galactofuranose (Galf) units of galactan. Obvious increased and selective synthesis of C₅₀-P-P-GlcNAc-Rha-Galf-Galf, the earliest product in the pathway leading to the fully polymerized galactan, was observed, suggesting that Rv3782 encodes a GalTr involved in the first stages of galactan synthesis. Time course experiments pointed to a possible bifunctional enzyme responsible for the initial synthesis of C₅₀-P-P-GlcNAc-Rha-Galf, followed by immediate conversion to C₅₀-P-P-GlcNAc-Rha-Galf-Galf. Thus, Rv3782 appears to be the initiator of galactan synthesis, while Rv3808c continues with the subsequent polymerization events.

This article has been cited by other articles:

• Belanova, M., Dianiskova, P., Brennan, P. J., Completo, G. C., Rose, N. L., Lowary, T. L., Mikusova, K. (2008). Galactosyl Transferases in Mycobacterial Cell Wall Synthesis. J. Bacteriol. 190: 1141-1145 [Abstract] [Full Text]  
• Berg, S., Kaur, D., Jackson, M., Brennan, P. J (2007). The glycosyltransferases of Mycobacterium tuberculosis--roles in the synthesis of arabinogalactan, lipoarabinomannan, and other glycoconjugates. Glycobiology 17: 35R-56R [Abstract] [Full Text]