INHIBITION OF INSULIN RELEASE BY SYNTHETIC PEPTIDES SHOWS THAT THE H3REGION AT THE C-TERMINAL DOMAIN OF SYNTAXIN-1 IS CRUCIAL FOR CA2- BUTNOT FOR GUANOSINE 5'-[GAMMA-THIO]TRIPHOSPHATE-INDUCED SECRETION()

Recently, we have described the presence and possible role of syntaxin in pancreatic beta-cells by using monoclonal antibodies [F. Martin, F . Moya, L. M. Gutierrez, J. A. Reig, B. Soria (1995) Diabetologia 38, 860-863]. In order to characterize further the importance of specific domains of this protein, the functional role of a particular region of the syntaxin-1 molecule has now been investigated by using two synthe tic peptides, SynA and SynB, corresponding to two portions of the H3 r egion at the C-terminal domain of the protein, residues 229-251 and 19 7-219 respectively. Functional experiments carried out in permeabilize d pancreatic beta-cells demonstrate that these peptides inhibit Ca2+-d ependent insulin release in a dose-dependent manner. This effect is sp ecific because peptides of the same composition but random sequence do not show the same effect. In contrast with this inhibitory effect on Ca2+-induced secretion, both peptides increase basal release. However, under the same conditions, SynA and SynB do not affect guanosine 5'-[ gamma-thio]triphosphate-induced insulin release. These results demonst rate that specific portions of the H3 region of syntaxin-1 are involve d in critical protein-protein interactions specifically during Ca2+-in duced insulin secretion.