Abstract
Using pressure-tuning Fourier transform infrared spectroscopy to study an in vitro system consisting of actin and distearoyl-phosphatidylcholine (DSPC) liposomes, we have determined the mechanism of interaction between actin and membrane lipids. This interaction results in a significant conformational change in actin molecules. Analysis of the amide I band of actin shows an increase in the beta-sheets to alpha-helix ratio, in random turns, and in interactions between actin monomers. In the absence of lipids, the actin molecules are denatured by pressures of 8 x 10(8) Pa and more, which give rise to a random organization of the peptide chain. However, in the presence of DSPC liposomes, pressure greater than 2 x 10(8) Pa induces a change in actin conformation, which is dominated by strongly interacting beta-sheets. As the spectra of the lipid molecules are not changed by the presence of actin, the organization of the lipid molecules in the bilayer is not affected by the protein. It is concluded from these results that this interaction of actin with membrane lipids involves very few lipid molecules. These lipid molecules may interact with actin at a few specific sites on the protein.