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.
Highlights
Dystrophin, the protein product of the Duchenne muscular dystrophy locus, is a large membrane-associated cytoskeletal protein [1]
In order to understand the function of this protein in skeletal muscle, it is important to establish the molecular organization of dystrophin in the context of the membrane cytoskeleton
Cloning of Human 2-Syntrophin—Having previously amplified a PCR product corresponding to EST25263 [13], we were able to radiolabel this product and isolate full-length cDNA clones
Summary
Dystrophin, the protein product of the Duchenne muscular dystrophy locus, is a large membrane-associated cytoskeletal protein [1]. This 58-kDa synaptic protein copurifies with dystrophin and is known as syntrophin (6 –9). Dystrophinassociated syntrophin isolated from rabbit skeletal muscle is heterogeneous; it appears as a triplet by one-dimensional SDSelectrophoresis, and when separated by two-dimensional gel electrophoresis, appears as two clusters of 58-kDa proteins with different isoelectric points (pI), one which is slightly acidic (␣, pI ϭ 6.4) and the other which is quite basic (, pI ϭ 9) [10]. From all the available sequences, we proposed that there are at least three syntrophin genes in the mammalian genome From their predicted amino acid sequences and their calculated pI values, the acidic isoform was named ␣1-syntrophin, and the two basic isoforms 1-syntrophin and 2-syntrophin (see Table I)
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