Biosynthesis of the mycobacterial methylmannose polysaccharide. Identification of an alpha 1----4-mannosyltransferase.
The methylmannose polysaccharide, found in the cytoplasm of Mycobacterium smegmatis, is composed of 3-O-methylmannose units joined in alpha 1----4 linkage in a chain terminated by unmethylated mannose at the nonreducing end. An alpha 1----4-mannosyltransferase, one of the two enzymes involved in methylmannose polysaccharide elongation, has been identified in cell extracts. The activity is membrane-associated and catalyzes the transfer of mannose from GDP-mannose to oligomeric acceptors composed of 4 to 12 3-O-methylmannoses. 1H NMR spectroscopy and alpha-mannosidase digestion confirm that the mannose is attached by an alpha 1----4 linkage. In competition studies, the enzyme utilizes shorter oligomeric acceptors preferentially. The Km of the mannosyltransferase for MeMan4-OCH3 is 15-20 microM, for MeMan6-OCH3 it is 75-85 microM, and for GDP-mannose it is 55 microM.
D002462:Cell Membrane / Q000201:enzymology; D002850:Chromatography, Gel; D006602:Hexosyltransferases / Q000378:metabolism*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008364:Mannosyltransferases / Q000378:metabolism*; D008759:Methylglycosides / Q000378:metabolism*; D008766:Methylmannosides / Q000378:metabolism*; D009161:Mycobacterium / Q000201:enzymology*; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D013045:Species Specificity
D008759:Methylglycosides; D008766:Methylmannosides; D011135:Polysaccharides, Bacterial; D006602:Hexosyltransferases; D008364:Mannosyltransferases; C040827:alpha 1-4-mannosyltransferase