Inhibition of insulin release by synthetic peptides shows that the H3 region at the C-terminal domain of syntaxin-1 is crucial for Ca²⁺- but not for guanosine 5′-[γ-thio]triphosphate-induced secretion Available to Purchase

Recently, we have described the presence and possible role of syntaxin in pancreatic β-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 synthetic peptides, SynA and SynB, corresponding to two portions of the H3 region at the C-terminal domain of the protein, residues 229–251 and 197–219 respectively. Functional experiments carried out in permeabilized pancreatic β-cells demonstrate that these peptides inhibit Ca²⁺- dependent insulin release in a dose-dependent manner. This effect is specific 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´-[γ-thio]triphosphate-induced insulin release. These results demonstrate that specific portions of the H3 region of syntaxin-1 are involved in critical protein–protein interactions specifically during Ca²⁺-induced insulin secretion.