The I/LWEQ module is a conserved sequence that we have identified as an actin-binding motif in the metazoan focal adhesion protein talin and the yeast protein Sla2p. Both of these proteins are associated with the actin cytoskeleton in cells. To better establish the value of the I/LWEQ module for prediction of actin-binding function, we have applied a functional genomics approach. Analysis of the 23 available I/LWEQ module sequences supports the division of I/LWEQ protein superfamily into four groups: (1) metazoan talin, (2) Dictyostelium discoideum talin homologs TalA/B, (3) metazoan Hip1p, and (4) yeast Sla2p. We show here that I/LWEQ modules from each major group bind to F-actin in vitro and that GFP-fusion proteins of the I/LWEQ modules of talin and Sla2p bind to F-actin in vivo. Therefore, the presence of an I/LWEQ module is strongly predictive of protein-actin interactions. The structural and functional conservation of the I/LWEQ module across the phylogenetic distance between cellular slime molds and mammals implies that the role of the I/LWEQ module is to connect diverse proteins involved in distinct cellular processes, including cell adhesion, cytoskeletal organization, and cell differentiation, to the actin cytoskeleton.
Copyright 1999 Academic Press.