Synip: A Novel Insulin-Regulated Syntaxin 4–Binding Protein Mediating GLUT4 Translocation in Adipocytes

Abstract Insulin-stimulated glucose transport and GLUT4 translocation require regulated interactions between the v-SNARE, VAMP2, and the t-SNARE, syntaxin 4. We have isolated a novel syntaxin 4–binding protein, Synip, which specifically interacts with syntaxin 4. Insulin induces a dissociation of the Synip:syntaxin 4 complex due to an apparent decrease in the binding affinity of Synip for syntaxin 4. In contrast, the carboxy-terminal domain of Synip does not dissociate from syntaxin 4 in response to insulin stimulation but inhibits glucose transport and GLUT4 translocation. These data implicate Synip as an insulin-regulated syntaxin 4–binding protein directly involved in the control of glucose transport and GLUT4 vesicle translocation.