Browsing by Author "Christie, MP"

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    Low resolution structural studies of Munc18c complexed with a Syntaxin-4/T4- Lysozyme Fusion
    (Australian Institute of Nuclear Science and Engineering, 2016-11-29) Whitten, AE; Rehman, AU; Hu, SH; Tnimov, Z; Christie, MP; King, GJ; Jarrott, RJ; Norwood, S; Alexandrov, K; Collins, BM; Martin, JL
    Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNARE) act at every intracellular trafficking pathway. Cognate v-SNAREs (e.g. VAMP) and t-SNAREs (Syntaxin (Sx) and SNAP) form a high affinity SNARE ternary complex (Sx-SNAP-VAMP) that brings the membranes together, triggering fusion. Syntaxins consist of a SNARE motif, and a three-helix bundle. In an open confirmation, the SNARE motif is free to form the SNARE ternary complex (stimulating fusion), but in the closed confirmation fusion is inhibited. Sec1p/Munc18 (SM) proteins bind to Sx, regulating SNARE mediated fusion [1], but their exact role is not well understood [2-4]. In the cell, Sx is bound to the membrane, and it is possible that this tethering may influence the manner in which it interacts with other proteins. As a means of investigating structural changes arising due to tethering, here, we investigate how the addition of a C-terminal T4-Lysozyme (soluble) fusion to Sx4 modulates its interaction with Munc18c. Preliminary low-resolution models of the Munc18c-Sx4T4 complex optimized against small-angle scattering data will be presented.
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    Low-resolution solution structures of Munc18:Syntaxin protein complexes indicate an open binding mode driven by the Syntaxin N-peptide
    (National Academy of Sciences, 2012-06-19) Christie, MP; Whitten, AE; King, GJ; Hu, SH; Jarrott, RJ; Chen, KE; Duff, AP; Callow, P; Collins, BM; James, DE; Martin, JL
    When nerve cells communicate, vesicles from one neuron fuse with the presynaptic membrane releasing chemicals that signal to the next. Similarly, when insulin binds its receptor on adipocytes or muscle, glucose transporter-4 vesicles fuse with the cell membrane, allowing glucose to be imported. These essential processes require the interaction of SNARE proteins on vesicle and cell membranes, as well as the enigmatic protein Munc18 that binds the SNARE protein Syntaxin. Here, we show that in solution the neuronal protein Syntaxin1a interacts with Munc18-1 whether or not the Syntaxin1a N-peptide is present. Conversely, the adipocyte protein Syntaxin4 does not bind its partner Munc18c unless the N-peptide is present. Solution-scattering data for the Munc18-1:Syntaxin1a complex in the absence of the N-peptide indicates that this complex adopts the inhibitory closed binding mode, exemplified by a crystal structure of the complex. However, when the N-peptide is present, the solution-scattering data indicate both Syntaxin1a and Syntaxin4 adopt extended conformations in complexes with their respective Munc18 partners. The low-resolution solution structure of the open Munc18:Syntaxin binding mode was modeled using data from cross-linking/mass spectrometry, small-angle X-ray scattering, and small-angle neutron scattering with contrast variation, indicating significant differences in Munc18:Syntaxin interactions compared with the closed binding mode. Overall, our results indicate that the neuronal Munc18-1:Syntaxin1a proteins can adopt two alternate and functionally distinct binding modes, closed and open, depending on the presence of the N-peptide, whereas Munc18c:Syntaxin4 adopts only the open binding mode. © 2012, National Academy of Sciences.