On the Ball

Many important cellular processes occur at membrane surfaces, and many drugs and infectious disease agents target proteins in cell membranes. Studying these poorly understood processes may soon get easier, thanks to a new technique for detecting binding events that occur at membrane surfaces.

The method, developed by University of California, Berkeley, assistant professor of chemistry Jay T. Groves, depends on coating microscopic silica beads with a phospholipid bilayer [Nature, 427, 139 (2004)]. The fluidity of the bead-supported bilayer mimics that of natural cell membranes, and it's simple to embed fully functional ligands or protein receptors.

When dispersed in water, these membrane-coated beads spontaneously form two-dimensional colloidal crystals. The beads' order is disrupted, however, when a protein receptor that binds to a ligand in the membrane is added to the solution. The dynamic process can be observed under a conventional light microscope.

But direct observation of the process isn't necessary, Groves notes. His team uses statistical methods to track changes in the spatial order of the beads. They're now working to adapt the method for high-throughput screening for protein-ligand interactions on membrane surfaces.

Biophysicist Thomas M. Bayerl of the University of Würzburg, in Germany, calls the study a "promising start," noting that Groves's method allows sensitive and specific detection of molecular interactions at the membrane surface. And unlike other methods, it doesn't require fluorescent labels or sophisticated techniques. But it remains to be seen how general the new method is, he says.