Virtual adherens junctions

JCB • VOLUME 172 • NUMBER 1 • 2006 4 Virtual adherens junctions he textbook model of adherens junctions has been exploded, or severed, by Bill Weis, Soichiro Yamada, Frauke Drees, Sabine Pokutta, and W. James Nelson (Stanford University School of Medicine, Stanford, CA). There is no direct link, they say, between cadherin, via and -catenin, to actin. Weis’s original goal was ambitious—a structural understanding of adherens junctions. First came biochemistry. “It was only when we attempted to reconstitute [the junctions],” he says, “that we found that nobody had actually done it before.” The textbook model “was all based on binary interactions.” The group now reports that catenin can either bind as a monomer to -catenin and thus cadherin, or bind as a homodimer to actin. But the binding events are mutually exclusive so there is no direct link from cadherin to actin. Consistent with this, cadherins and actin have very different dynamics. Weis stresses that their two model systems—clustered soluble fragments of T