Syntaxin Binding Mechanism and Disease-Causing Mutations in Munc18-2Hackmann, Y., Graham, S.C., Ehl, S., Hoening, S., Lehmberg, K., Arico, M., Owen, D.J., Griffiths, G.G.
(2013) Proc Natl Acad Sci U S A 110: E4482
- PubMed: 24194549
- DOI: https://doi.org/10.1073/pnas.1313474110
- Primary Citation of Related Structures:
- PubMed 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.
Cambridge Institute for Medical Research, University of Cambridge Biomedical Campus, University of Cambridge, Cambridge CB2 0XY, United Kingdom.