FIG. 1.

Pathway for the biosynthesis of mycobacterial arabinogalactan. The sequence of reactions is based on identification of GL-1 through GL-5 and the lipid-linked arabinogalactan polymer in cell-free systems containing mycobacterial membranes and cell wall fractions (21-23, 25). GlcNAc-1-P transferase WecA (Rv1302) is proposed to be responsible for step 1 (21); the rhamnosyl transferase WbbL (Rv3265) catalyzes step 2 (26). Subsequent reaction 3 and/or 4 is proposed in this study and previously (22) to be catalyzed by Rv3782. Step 6 represents a series of galactofuranosyl additions catalyzed by Rv3808c. Several arabinosyl transferases involved in reactions under step 7 have been described, such as the Emb proteins (3), AftA (1), and AftB (34).