Lipoarabinomannan (LAM) biosynthesis

Lipoarabinomannan (LAM), as well as structurally related lipomannan (LM) and phosphatidylinositol mannosides (PIMs), are major glycolipids found on the mycobacterial cell wall. LAM is synthesized from phosphatidylinositol (PI) and in a biochemical pathway of PI => PIMs => LM =>LAM. Structually, LAM and LM are an extension of PIMs containing an alpha1,6-linked mannan core with alpha1,2-monomannose side chains. The mannan core of LAM is in turn arabinosylated by a linear alpha1,5-linked Araf backbone, punctutated by alpha1,3-linked branching. LAM can be substituted by several capping motifs, which determine the ability of LAM to modulate the immune response through the interaction with different receptors containing C-type lectins (map04625). It has been shown that the immunomodulatory properties of LAM and related glycolipids contribute to the survival of Mycobacteriaum tuberculosis, the causative agent of tuberculosis (map05152).