The interaction of plectin with actin: evidence for cross-linking of actinfilaments by dimerization of the actin-binding domain of plectin

Plectin is a major component of the cytoskeleton and is expressed in a wide variety of cell types. It plays an important role in the integrity of the cytoskeleton by crosslinking the three filamentous networks and stabilizing cell-matrix and cell-cell contacts. Sequence analysis showed that plectin contains a highly conserved actin-binding domain, consisting of a pair of c alponin-like subdomains. Using yeast two-hybrid assays in combination with in vitro binding experiments, we demonstrate that the actin-binding domain of plectin is fully functional and preferentially binds to polymeric actin. The sequences required for actin binding were identified at the C-terminal end of the first calponin homology domain within the actin-binding domain of plectin. We found that the actin-binding domain of plectin is able to bu ndle actin filaments and we present evidence that this is mediated by the d imerization of this domain. In addition we also show that plectin and anoth er member of the plakin family, dystonin, can heterodimerize by their actin -binding domains. We propose a new mechanism by which plectin and possibly also other actin-binding proteins can regulate the organization of the F-ac tin network in the cell.