INHIBITION OF THE BINDING OF SNAP-23 TO SYNTAXIN-4 BY MUNC18C

SNARE proteins have been implicated in the insulin-induced translocati on of vesicles containing the GLUT4 glucose transporter to the plasma membrane of adipocytes. The role of the target SNARE SNAP-25 or its ho mologs in this process was investigated by screening a mouse adipocyte cDNA library with rat SNAP-25 and human SNAP-23 cDNA probes. Both pos itive clones isolated encoded a protein with 87% sequence identity to human SNAP-23, and which was therefore designated mouse SNAP-23. Immun oblot and immunofluorescence analyses revealed that SNAP-23 is located predominantly in the plasma membrane of 3T3-L1 adipocytes incubated i n the absence or presence of insulin. Of syntaxins 1 to 5, SNAP-23 bou nd with the highest affinity to syntaxins 1 and 4 in the yeast two-hyb rid system. Expression of SNAP-23, syntaxin 4, and the syntaxin-bindin g protein Munc18c in COS cells revealed that Munc18c reduced the amoun t of SNAP-23 bound to syntaxin 4 in a concentration-dependent manner. These results suggest that the binding of SNAP-23 to syntaxin 4 is inh ibited by Munc18c in adipocytes. (C) 1997 Academic Press.