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

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