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.
CITATION STYLE
Whitten, A. E., Jarrott, R. J., Hu, S. H., Duff, A. P., King, G. J., Martin, J. L., & Christie, M. P. (2019). Studying Munc18:syntaxin interactions using small-angle scattering. In Methods in Molecular Biology (Vol. 1860, pp. 115–144). Humana Press Inc. https://doi.org/10.1007/978-1-4939-8760-3_7
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