Primary sequence of paxillin contains putative SH2 and SH3 domain binding motifs and multiple LIM domains: identification of a vinculin and pp125Fak- binding region

Abstract

Paxillin is a cytoskeletal protein involved in actin- membrane attachment at sites of cell adhesion to the extra- cellular matrix. Extensive tyrosine phosphorylation of this protein occurs during integrin-mediated cell adhesion, embryonic development, fibroblast transformation and following stimulation of cells by mitogens that operate through the family of seven membrane-spanning G- protein-coupled receptors. Paxillin binds in vitro to the focal adhesion protein vinculin as well as to the SH3 domain of c-src and, when tyrosine phosphorylated, to the SH2 domain of v-crk. Here, we report the complementary DNA, and derived amino acid sequence, that codes for approximately 90% of the paxillin protein. We have iden- tified a region in the amino-terminal half of the protein that supports the binding of both vinculin and the focal adhesion tyrosine kinase, pp125Fak. Although there is no significant overall homology with other identified proteins, the carboxyl third of paxillin contains one LIM domain and three LIM-like sequences. The LIM motif is common to a number of transcription factors and to two other focal adhesion proteins, zyxin and cysteine-rich protein. In addition to several potential tyrosine phosphorylation sites there are five tyrosine-containing sequences that conform to SH2-binding motifs. The protein also contains a short proline-rich region indicative of a SH3-binding domain. Taken together, these data suggest that paxillin is a unique cytoskeletal protein capable of interaction with a variety of intracellular signaling, and structural, molecules important in growth control and the regulation of cytoskeletal organization. The homology with zyxin and cysteine-rich protein defines a novel family of LIM-con- taining molecules associated with sites of actin-membrane attachment.