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  • Title: Munc18-1 stabilizes syntaxin 1, but is not essential for syntaxin 1 targeting and SNARE complex formation.
    Author: Toonen RF, de Vries KJ, Zalm R, Südhof TC, Verhage M.
    Journal: J Neurochem; 2005 Jun; 93(6):1393-400. PubMed ID: 15935055.
    Abstract:
    Munc18-1, a member of the Sec1/Munc18 (SM) protein family, is essential for synaptic vesicle exocytosis. Munc18-1 binds tightly to the SNARE protein syntaxin 1, but the physiological significance and functional role of this interaction remain unclear. Here we show that syntaxin 1 levels are reduced by 70% in munc18-1 knockout mice. Pulse-chase analysis in transfected HEK293 cells revealed that Munc18-1 directly promotes the stability of syntaxin 1, consistent with a chaperone function. However, the residual syntaxin 1 in munc18-1 knockout mice is still correctly targeted to synapses and efficiently forms SDS-resistant SNARE complexes, demonstrating that Munc18-1 is not required for syntaxin 1 function as such. These data demonstrate that the Munc18-1 interaction with syntaxin 1 is physiologically important, but does not represent a classical chaperone-substrate relationship. Instead, the presence of SNARE complexes in the absence of membrane fusion in munc18-1 knockout mice indicates that Munc18-1 either controls the spatially correct assembly of core complexes for SNARE-dependent fusion, or acts as a direct component of the fusion machinery itself.
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