Protein-Lipid Alliances

A better picture of the poorly understood dynamics of biological membranes is now available, thanks to a team of Scandinavian researchers. Ilpo Vattulainen of Finland’s Tampere University of Technology and coworkers report using computer simulations to investigate individual proteins in lipid bilayers and found that proteins in cell membranes diffuse as complexes with 50 to 100 lipid molecules (J. Am. Chem. Soc., DOI: 10.1021/ja101481b). They determined that lipids close to a protein move much more slowly than the rest of the bilayer and that lipid motion is strongly correlated with the protein’s motion. In real membranes, the researchers note, the lipid-to-protein ratio is about 50:1. On that basis, they speculate that there are no “free” bulk lipids in biological membranes. In addition, the few lipids observed in crystal structures of membrane proteins “are apparently just the tip of the iceberg,” they write, because the protein-lipid complex appears to contain many more lipids. “These conclusions are certainly quite intriguing, but we have so far no experimental evidence of the significance of these simulations in real membranes,” says Petra Schwille, a biophysicist who studies biological membranes at the Technical University of Dresden, in Germany.