Protective effect of lipidic surfaces against pressure-induced conformational changes of poly(L-lysine)

Poly(L-lysine) bound to phosphatidylglycerol or phosphatidic acid bilayers was submitted to hydrostatic pressure in a diamond anvil cell to investigate whether the lipidic surfaces can protect the polypeptide against pressure-induced conformational transformations. The amide I region of the infrared spectrum of dimyristoylphosphatidic acid bound polylysine shows that most of the polypeptide retains its beta-sheet structure up to 19 kbar, while it is known to convert entirely to alpha-helix at approximately 2 kbar in the absence of the lipid [Carrier, D., Mantsch, H.H., & Wong, P.T.T. (1989) Biopolymers (in press)]. The simultaneous binding of the polypeptidic molecules to two opposing bilayers appears to be required in order to preserve the beta-sheet structure at pressures over approximately 9 kbar: a small proportion of the polypeptide, most likely the molecules at the surface of the aggregated bilayers, was found to convert to unordered and eventually to alpha-helical conformations in the pressure range 9-19 kbar. The decrease from 1612 to 1606 cm-1 of the frequency of the major beta-sheet component of the infrared amide I band as the pressure is raised to 6 kbar indicates a strengthening of the interchain hydrogen bonds. The high-pressure infrared spectra of polylysine bound to dimyristoyl- and dipalmitoylphosphatidylglycerol show that the polypeptide remains alpha-helical up to approximately 12 kbar, though the changes in the bandshape indicate an increase in hydrogen bond strength. The formation of a small amount of beta-sheet was observed during decompression and is attributed to the effect of dehydration on the polypeptidic molecules located at the surface of the aggregates.(ABSTRACT TRUNCATED AT 250 WORDS)