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GLYCOPEPTIDOLIPIDS
Definition

Glycopeptidolipids (GPL) are abundant components of the cell walls of several species of mycobacteria. They have been implicated in the pathogenesis of the opportunistic mycobacteria belonging to the Mycobacterium avium complex.

MYCOBACTERIA have characteristic lipid-rich cell envelopes that afford the cells protection from desiccation, chemical disinfectants and some antibiotics. The mycobacterial cell envelope has a multilaminar structure with the outermost layer comprising an asymmetric lipid bilayer with mycolic acids on the inner leaflet.

The composition of the outer leaflet varies between species of mycobacteria but generally contains a mixture of glycolipids and phospholipids. Glycopeptidolipids (GPLs) occur among the lipids of the outer layer of some non- tuberculous mycobacteria that cause infections (Mycobacterium avium complex, Mycobacterium peregrinum, M. abscessus) and saprophytic mycobacteria

The surface glycopeptidolipids of mycobacteria: Structures and biological properties
The identification & characterization of structure of GPLs was initiated by the work of Schaefer, Marks, and Jenkins in the 1960s and 1970s. One of the most important opportunistic pathogens associated with acquired immunodeficiency syndrome (AIDS) is the M. avium complex. M. avium infections are found in up to 70 percent of individuals in advanced stages of AIDS. It is apparent that M. avium can replicate in host macrophages and persist for long periods. This group of mycobacteria are distinguished by the presence of unique, highly antigenic, surface-located lipids known as the glycopeptidolipids (GPLs). GPLs are composed of a lipopeptide core structure containing a 3-hydroxy or a 3-methoxy C26-C33 fatty acyl chain N-linked to a tripeptide-amino-alcohol core generally made up of d-phenylalanine-d-allo-threonine-d-alanine-l-alaninol. This lipopeptide core is glycosylated with the allo-threonine glycosidically linked to a 6-deoxy-α-l-talose (6-deoxytalose) and the alaninol glycosidically linked to an α-l-rhamnose (rhamnose).