MOLECULAR PACKING OF CORD FACTOR AND ITS INTERACTION WITH PHOSPHATIDYLINOSITOL IN MIXED MONOLAYERS

Cord factor (trehalose 6,6'-dimycolate, CF) is a glycolipid located in the outer mycobacterial cell wall that is implicated in the pathogene sis of mycobacteria. Furthermore, CF is a convenient model for studyin g mycolic acid residues, the major lipid constituents of the mycobacte rial cell walt that are believed to form a barrier against drug penetr ation. The surface properties of CF and its interactions with phosphat idylinositol (Pt) have been investigated using the monolayer technique . During compression/expansion/recompression cycles, CF monolayers swi tch from a loosely packed to a more tightly packed structure. The chan ge in surface properties suggests a molecular rearrangement, perhaps i nvolving interdigitation of long and short chains of the CF molecules. In CF-PI monolayers, maximal lateral packing density occurs between 0 .5 and 0.7 mote fraction CF, which is close to the relative compositio n of mycolic acid residues and shorter-chain lipids in the mycobacteri al cell wall. Low concentrations of CF increase the order in PI monola yers, consistent with CF toxicity involving rigidification of cell mem branes.