S-nitrosylation of syntaxin 1 at Cys145 is a regulatory switch controlling Munc18-1 binding

International audience ; Exocytosis is regulated by nitric oxide (NO) in many cell types, including neurons. Here we show that syntaxin 1a is a substrate for S-nitrosylation and that NO disrupts the binding of Munc18-1 to the closed conformation of syntaxin 1a in vitro. In contrast, NO does not inhibit SNARE complex formation or binding of Munc18-1 to the SNARE complex. Cys145 of syntaxin 1a is the target of NO, as a non-nitrosylatable C145S mutant is resistant to NO and novel nitrosomimetic C145 mutants mimic the effect of NO on Munc18-1 binding in vitro. Furthermore, expression of nitrosomimetic syntaxin 1a in living cells affects Munc18-1 localisation and alters exocytosis release kinetics and quantal size. Molecular dynamics simulations suggest that NO regulates the syntaxin-Munc18 interaction by local rearrangement of the syntaxin linker and H3c regions. Thus, S-nitrosylation of Cys145 may be a molecular switch to disrupt Munc18-1 binding to the closed conformation of syntaxin 1a, thereby facilitating its engagement with the membrane fusion machinery.