Mouse α1- and β2-Syntrophin Gene Structure, Chromosome Localization, and Homology with a Discs Large Domain

Abstract

The syntrophin family of dystrophin-associated proteins consists of three isoforms, ␣1, ␤1, and ␤2, each encoded by a distinct gene. We have cloned and characterized the mouse ␣1-and ␤2-syntrophin genes. The mouse ␣1-syntrophin gene (>24 kilobases) is comprised of eight exons. The mouse ␤2-syntrophin gene (>33 kilobases) contains seven exons, all of which have homologues at the corresponding position in the ␣1-syntrophin gene. Primer extension analysis reveals two transcription initiation sites in the ␣1-syntrophin gene and a single site in the ␤2-syntrophin gene. The sequence immediately 5 of the transcription start sites of both genes lacks a TATA box but is GC-rich and has multiple putative SP1 binding sites. The ␣1-syntrophin gene is located on human chromosome 20 and mouse chromosome 2, while the ␤2-syntrophin gene is on human chromosome 16 and mouse chromosome 8. Analysis of the amino acid sequence of the syntrophins reveals the presence of four conserved domains. The carboxylterminal 56 amino acids are highly conserved and constitute a syntrophin unique domain. Two pleckstrin homology domains are located at the amino-terminal end of the protein. The first pleckstrin homology domain is interrupted by a domain homologous to repeated sequences originally found in the Drosophila discs-large protein.Syntrophin is a peripheral membrane protein of M r ϳ58,000 that was first identified in the postsynaptic membrane of Torpedo electric organ and subsequently shown to be present in many mammalian tissues (1). Interest in syntrophin came first from its location at the neuromuscular junction and more recently from the demonstration that it is directly associated with dystrophin, the product of the Duchenne/Becker muscular dystrophy gene. Although the precise function of syntrophin is unknown, a potential role for the dystrophin-associated proteins in agrin-stimulated nicotinic acetylcholine receptor clustering has implicated syntrophin in the process of synaptogenesis (2).Three different but highly conserved syntrophin isoforms encoded by distinct genes have been identified and cloned. Each syntrophin has approximately 50% amino acid identity with the other two (3). The three syntrophins can be separated into two classes based on isoelectric point (4). The acidic isoform, ␣1-syntrophin, (pI ϳ6.7) has been cloned from Torpedo, mouse, rabbit, and human (5-7). There are two basic forms, ␤1-and ␤2-syntrophin (pI ϳ 9.0). A full-length human cDNA encoding ␤1-syntrophin has been cloned, and the gene has been localized to human chromosome 8q23-24 (8). Partial clones encoding mouse and human ␤2-syntrophin have been reported previously (5,8).The function of syntrophin is likely to be related to its association with dystrophin and other members of the dystrophin protein family (9 -13). Proteins of the dystrophin family are derived from a combination of three genes, the use of alternative promoters within these genes, and alternative splicing. Dystrophin, the major product in skeletal muscle, is a 427-kDa protein with an actin-bi...

Potassium channel Kir4.1 macromolecular complex in retinal glial cells

“…2B, top). Syntrophins have been shown to migrate at 58 kDa on SDS-PAGE (Froehner et al, 1987;Adams et al, 1995;Suzuki et al, 1995), which is consistent with the band seen on our blot.…”

Cytoskeletal Basis of Ion Channel Function in Cardiac Muscle

“…53,54,55 Syntrophins contain two pleckstrin homology (PH) domains, a PDZ domain, and a syntrophin-unique (SU) C-terminal region. The interaction between syntrophins and dystrophin occurs at the PH domain distal to the syntrophin Nterminus and through the highly conserved SU domain.…”

An Apical PDZ Protein Anchors the Cystic Fibrosis Transmembrane Conductance Regulator to the Cytoskeleton

“…To test the specificity of the interaction between CFTR and EBP50, we performed assays using a peptide derived from the COOH terminus of the skeletal muscle voltage-gated sodium channel (SkM2) as an affinity ligand. It is known that the SkM2 peptide can precipitate syntrophins from lysates via a PDZ interaction (16,34). SkM2 failed to bind EBP50 (Fig.…”