Influence of the glycopeptidic moiety of mycobacterial glycopeptidolipids on their lateral organization in phospholipid monolayers

Glycopeptidolipids (GPLs) from the cell wall of opportunistic pathogenic mycobacteria are potential factors of pathogenicity which can interact with biological membranes. GPL suspensions uncouple oxidative phosphorylation of mitochondria and increase membrane permeability of liposomes. Heavily glycosylated GPLs are less active than lightly glycosylated ones. GPL-phospholipid interactions into preformed mixed films at the air-water interface were investigated in order to understand the permeabilization efficiency differences among GPLs. Polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) was used to determine, in situ, the organization of GPL and of 1,2-di(perdeuteropalmitoyl)phosphatidylcholine (DPPC) molecules in mixed films. Compression isotherms of GPL alone or mixed with DPPC in various proportions showed that the less the GPL was glycosylated the higher its miscibility with DPPC, PMIRRAS studies indicated that low miscibility may result from large self-association of GPL molecules in beta-sheet structures. Low glycosylated GPL molecules increased disorder of DPPC acyl chains. Based on these results, an explanatory model is proposed for membrane permeabilization. Increase of passive permeability may arise from disruption of phospholipid packing induced by GPL molecules. GPL segregation is proposed as the cause of low activity of GPL with high sugar content, by decreasing the number of GPL molecules interacting with phospholipids. (C) 2000 Elsevier Science B.V. All rights reserved.