Synthetic mannosides act as accepters for mycobacterial alpha 1-6 mannosyltransferase

A series of synthetic mannosides was screened in a cell-free system for the ir ability to act as acceptor substrates For mycobacterial mannosyltransfer ases. Evaluation of these compounds demonstrated the incorporation of [C-14 ]Man From GDP-[C-14]Man into a radiolabeled organic-soluble fraction and an alysis by thin layer chromatography and autoradiography revealed the format ion of two radiolabeled products. Each synthetic acceptor was capable of ac cepting one or two mannose residues. resulting in a major and a minor manno sylated product. Both products from each acceptor were isolated and their m ass was confirmed by fast-atom bombardment-mass spectrometry (FABMS). Chara cterization of each mannosylated product by exo-glycosidase digestion, acet olysis and linkage analysis by gas chromatography-mass spectrometry of part ially per-O-methylated alditols, revealed only alpha1-6-linked products. In addition, the antibiotic amphomycin selectively inhibited the formation of mannosylated products suggesting polyprenolmonophosphate-mannose (C-35 (50 )-P-Man) was the immediate mannose donor in all mannosylation reactions obs erved. The ability of synthetic disaccharides to act as acceptor substrates in this system, is most Likely due to the action of a mycobacterial polypr enol-P-Man:mannan alpha1-6 mannosyltransferase involved in the biosynthesis of linear alpha1-6-linked lipomannan. (C) 2001 Elsevier Science Ltd. All r ights reserved.