In vitro characterization of native mammalian smooth-muscle protein synaptopodin 2

Abstract

An analysis of the primary structure of the actin-binding protein fesselin revealed it to be the avian homologue of mammalian synaptopodin 2 [Schroeter, Beall, Heid, and Chalovich (2008) Biochem. Biophys. Res. Commun. 371, 582–586]. We isolated two synaptopodin 2 isoforms from rabbit stomach that corresponded to known types of human synaptopodin 2. The purification scheme used was that developed for avian fesselin. These synaptopodin 2 forms shared several key functions with fesselin. Both avian fesselin and mammalian synaptopodin 2 bound to Ca2+–calmodulin, α-actinin and smooth-muscle myosin. In addition, both proteins stimulated the polymerization of actin in a Ca2+–calmodulin-dependent manner. Synaptopodin 2 has never before been shown to polymerize actin in the absence of α-actinin, to polymerize actin in a Ca2+–calmodulin-dependent manner, or to bind to Ca2+–calmodulin or myosin. These properties are consistent with the proposed function of synaptopodin 2 in organizing the cytoskeleton.