Laminin - 1 globular domains 3 and 4 induce heterotrimeric G protein binding to - syntrophin ’ s PDZ domain and alter intracellular Ca 2 in muscle

Zhou, Yan Wen, Shilpa A. Oak, Susan E. Senogles, and Harry W. Jarrett. Laminin1 globular domains 3 and 4 induce heterotrimeric G protein binding to -syntrophin’s PDZ domain and alter intracellular Ca in muscle. Am J Physiol Cell Physiol 288: C377– C388, 2005. First published September 22, 2004; doi:10.1152/ajpcell. 00279.2004.— -Syntrophin is a component of the dystrophin glycoprotein complex (DGC). It is firmly attached to the dystrophin cytoskeleton via a unique COOH-terminal domain and is associated indirectly with -dystroglycan, which binds to extracellular matrix laminin. Syntrophin contains two pleckstrin homology (PH) domains and one PDZ domain. Because PH domains of other proteins are known to bind the -subunits of the heterotrimeric G proteins, whether this is also a property of syntrophin was investigated. Isolated syntrophin from rabbit skeletal muscle binds bovine brain G subunits in gel blot overlay experiments. Laminin-1-Sepharose or specific antibodies against syntrophin, and -dystroglycan, or dystrophin precipitate a complex with G from crude skeletal muscle microsomes. Bacterially expressed syntrophin fusion proteins and truncation mutants allowed mapping of G binding to syntrophin’s PDZ domain; this is a novel function for PDZ domains. When laminin-1 is bound, maximal binding of Gs and G occurs and active Gs , measured as GTPS bound, decreases. Because intracellular Ca is elevated in Duchenne muscular dystrophy and Gs is known to activate the dihydropyridine receptor Ca channel, whether laminin also altered intracellular Ca was investigated. Laminin-1 decreases active (GTPS-bound) Gs , and the Ca channel is inhibited by laminin-1. The laminin 1-chain globular domains 4 and 5 region, the region bound by DGC -dystroglycan, is sufficient to cause an effect, and an antibody that specifically blocks laminin binding to -dystroglycan inhibits G binding by syntrophin in C2C12 myotubes. These observations suggest that DGC is a matrix laminin, G protein-coupled receptor.