Abstract
A superfamily of actin crosslinking proteins, the calponin-homology domain (CH) family is implicated in directing the assembly and controlling the organization of the cytoskeleton through a highly conserved actin binding domain (ABD). This domain, composed of a tandem pair of CH motifs, is found in actin crosslinking proteins such as fimbrin, alpha-actinin, spectrin, and dystrophin. In addition to its role in crosslinking actin filaments, a putative homologous ABD in intermediate filament-binding proteins, plectin, dystonin, and BPAGlnl, suggests a possible role in crosslinks between desmosomal and vimentin intermediate filaments and actin. Thus, the CH domain could integrate the functions of the actin and IF cytoskeletons by physically linking these structural systems. We present an atomic model for the complex of the CH domain and actin. In crosslinking proteins that organize actin into two and three dimensional networks or gels the ABDs lie at the ends of long, flexible molecules.