ROLE OF PHOSPHATIDYLETHANOLAMINE LIPIDS IN THE STABILIZATION OF PROTEIN-LIPID CONTACTS

We have investigated the effect of lipids with phosphatidylethanolamin e (PE) head groups on the stabilization of contacts between the trypto phan side chains of gramicidin and the lipid head groups. We initially developed two fluorescence methods that can be correlated to the spon taneous curvature of DOPC/DOPE and DOPC/DOPEme. One is based on bilaye r structure and measures the rotational motion of a probe located clos e to the membrane surface relative to a more deeply-buried probe. The second is based on surface hydration/polarity and measures the emissio n energy of a polarity-sensitive probe located on the membrane surface . We used these methods to estimate the pseudo-curvature (i.e., curvat ure obtained by fluorescence measurements) of lipids with dimyristyl c hains, and their pressure and temperature dependence. We then investig ated the stability of gramicidin tryptophan-lipid contacts in DMPC/DMP E as a function of temperature and pressure. Stability was assessed by tryptophan rotational motion as determined by fluorescence anisotropy , since rotational motion is limited when the indoles are hydrogen bon ded to the lipid head groups. The results suggest that the presence of PE lipids destabilizes these contacts due to either their smaller siz e relative to PC head groups, or their tendency to self-interact. Fluo rescence quenching studies support these results. (C) 1997 Elsevier Sc ience B.V.