Media highlights in the November issues of Biophysic...(ythmia. Why are lipid rafts not obs...)

Why are lipid rafts not observed in vivo?
Arun Yethiraj, University of Wisconsin and James C. Weisshaar, University of Wisconsin

Keywords: membrane proteins; phase transition; rafts

The cell membrane consists of many types of lipid and protein molecules. Some years ago the existence of lipid rafts, domains enriched in particular lipid molecules, was postulated. Many functions of the cell, including transport of matter from the outside (endocytosis) and signaling, during which specific proteins are gathered in a small area, have been attributed to rafts. The very existence of rafts in live cells, however, is hotly debated and direct evidence of rafts in vivo is sparse. While large rafts are readily observed in artificial membranes, attempts to observe analogous domains in live cells place an upper limit of 5 nanometers on their size.

In this paper Yethiraj and Weisshaar propose a new idea for why large rafts might not be present in cells. They suggest that proteins that span the membrane act as immobile obstacles, and show that the presence of these obstacles limits the size of lipid domains that can be formed. The presence of obstacles at only 5-10% by area suppresses the formation of large domains seen in artificial membranes. The structural and spatial heterogeneity of the membrane thus plays a crucial role in its biophysical properties.

Volume 93, Issue 10, November 15, 2007

High-resolution structure of a Na+/H+ antiporter dimer obtained by pulsed EPR distance measurements

Keywords: distance distribution; electron electron double resonance; membrane protein; protein-protein interaction; rotamer library; transporter

Our current knowledge about the molecu
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