Whitten AE, Jarrott RJ, Hu SH, Duff AP, King GJ, Martin JL, Christie MP. Studying
Munc18:Syntaxin Interactions Using Small-Angle Scattering.
Methods Mol Biol 2019;
1860:115-144. [PMID:
30317501 DOI:
10.1007/978-1-4939-8760-3_7]
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Abstract
The interaction between the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein syntaxin (Sx) and regulatory partner Sec/Munc18 (SM) protein is a critical step in vesicle fusion. The exact role played by SM proteins, whether positive or negative, has been the topic of much debate. High-resolution structures of the SM:Sx complex have shown that SM proteins can bind syntaxin in a closed fusion incompetent state. However, in vitro and in vivo experiments also point to a positive regulatory role for SM proteins that is inconsistent with binding syntaxin in a closed conformation. Here we present protocols we used for the expression and purification of the SM proteins Munc18a and Munc18c and syntaxins 1 and 4 along with procedures used for small-angle X-ray and neutron scattering that showed that syntaxins can bind in an open conformation to SM proteins. We also describe methods for chemical cross-linking experiments and detail how this information can be combined with scattering data to obtain low-resolution structural models for SM:Sx protein complexes.
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