Interactions of phosphoinositides with neuronal Munc18a/Syntaxin1a in vesicle trafficking

SH Hu1, RJ Jarrott1, MP Christie1, E Livingstone1, KJ King1, AE Whitten2, BM Collins1 and JL Martin1

  1. Institute for Molecular Bioscience, University of Queensland, Brisbane QLD 4072 Australia
  2. Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia

The Sec1/Munc18 (SM) proteins and the soluble N-ethymaleimide-sensitive factor attachment protein receptors (SNAREs) play an essential role in vesicle docking and fusion. The SNARE complex is composed of the target membrane SNAREs (t-SNAREs, Sx1a and SNAP25 in neurons) and the vesicle membrane SNARE (v-SNARE, VAMP2). The formation of the SNARE complex leads to membrane fusion. Neuronal SM protein Munc18a is essential for neurotransmission release and binds specifically to its cognate Sx1a. Structural studies have revealed the two binding modes of the interaction between Munc18a and Sx1a (N-terminal peptide and “closed”) (1). The Munc18a/Sx1a crystal structure showed that Munc18a binds to Sx1a in a closed conformation that is incompatible with SNARE complex formation (2, 3). We previously solved the crystal structure of Munc18a in complex with a non-cognate N-peptide from syntaxin4 (4). Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) was shown to interact with the polybasic residues of Sx1a (260KARRKK265) adjacent to the transmembrane domain (5, 6). The computational analysis has suggested that PI(4,5)P2 lipid regulates the phosphorylation of syntaxin N-terminus (7). By using lipid binding assays, we show that both Munc18a and Sx1a bind strongly to PI(3,5)P2, PI(4,5)P2 and also monophosphoinositides.
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