The Three Human Syntrophin Genes Are Expressed in Diverse Tissues, Have Distinct Chromosomal Locations, and Each Bind to Dystrophin and Its Relatives

Abstract

The syntrophins are a biochemically heterogeneous group of 58-kDa intracellular membrane-associated dystrophin-binding proteins. We have cloned and characterized human acidic (alpha 1-) syntrophin and a second isoform of human basic (beta 2-) syntrophin. Comparison of the deduced amino acid structure of the three human isoforms of syntrophin (together with the previously reported human beta 1-syntrophin) demonstrates their overall similarity. The deduced amino acid sequences of human alpha 1- and beta 2-syntrophin are nearly identical to their homologues in mouse, suggesting a strong functional conservation among the individual isoforms, Much like beta 1-syntrophin, human beta 2-syntrophin has multiple transcript classes and is expressed widely, although in a distinct pattern of relative abundance. In contrast, human alpha 1-syntrophin is most abundant in heart and skeletal muscle, and less so in other tissues. Somatic cell hybrids and fluorescent in situ hybridization were both used to determine their chromosomal locations: beta 2-syntrophin to chromosome 16q22-23 and alpha 1-syntrophin to chromosome 20q11.2. Finally, we used in vitro translated proteins in an immunoprecipitation assay to show that, like beta 1-syntrophin, both beta 2- and alpha 1-syntrophin interact with peptides encoding the syntrophin-binding region of dystrophin, utrophin/dystrophin related protein, and the Torpedo 87K protein.