title: Syntaxin binding mechanism and disease-causing mutations in Munc18-2.
abstract: Mutations in either syntaxin 11 (Stx11) or Munc18-2 abolish cytotoxic T lymphocytes (CTL) and natural killer cell (NK) cytotoxicity, and give rise to familial hemophagocytic lymphohistiocytosis (FHL4 or FHL5, respectively). Although Munc18-2 is known to interact with Stx11, little is known about the molecular mechanisms governing the specificity of this interaction or how in vitro IL-2 activation leads to compensation of CTL and NK cytotoxicity. To understand how mutations in Munc18-2 give rise to disease, we have solved the structure of human Munc18-2 at 2.6 Å resolution and mapped 18 point mutations. The four surface mutations identified (R39P, L130S, E132A, P334L) map exclusively to the predicted syntaxin and soluble N-ethylmaleimide-sensitive factor accessory protein receptor binding sites of Munc18-2. We find that Munc18-2 binds the N-terminal peptide of Stx11 with a ~20-fold higher affinity than Stx3, suggesting a potential role in selective binding. Upon IL-2 activation, levels of Stx3 are increased, favoring Munc18-2 binding when Stx11 is absent. Similarly, Munc18-1, expressed in IL-2-activated CTL, is capable of binding Stx11. These findings provide potential explanations for restoration of Munc18-Stx function and cytotoxicity in IL-2-activated cells.
authors.affiliation: Cambridge Institute for Medical Research, University of Cambridge Biomedical Campus, University of Cambridge, Cambridge CB2 0XY, United Kingdom.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Hackmann
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Graham
authors.forename: Stephan
authors.initials: S
authors.lastname: Ehl
authors.forename: Stefan
authors.initials: S
authors.lastname: Höning
authors.forename: Kai
authors.initials: K
authors.lastname: Lehmberg
authors.forename: Maurizio
authors.initials: M
authors.lastname: Aricò
authors.forename: David J
authors.initials: DJ
authors.lastname: Owen
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Griffiths
mesh_terms: D000818:Animals; D015153:Blotting, Western; D003460:Crystallization; D019143:Evolution, Molecular; D057809:HEK293 Cells; D006801:Humans; D007150:Immunohistochemistry; D007694:Killer Cells, Natural / Q000276:immunology* / Q000378:metabolism; D051359:Lymphohistiocytosis, Hemophagocytic / Q000235:genetics*; D008958:Models, Molecular; D051938:Munc18 Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation / Q000235:genetics; D011485:Protein Binding; D050765:Qa-SNARE Proteins / Q000378:metabolism*; D061987:Sf9 Cells; D018411:Spodoptera; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000378:metabolism
chemical_list: D051938:Munc18 Proteins; D050765:Qa-SNARE Proteins; C541732:STX11 protein, human; C497940:STXBP2 protein, human
keywords: immunodeficiency; membrane trafficking; secretory lysosomes