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: Yvonne Hackmann, Stephen C Graham, Stephan Ehl, Stefan Höning, Kai Lehmberg, Maurizio Aricò, David J Owen, Gillian M Griffiths
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 110 Issue 47 Pg. E4482-91 (Nov 19 2013) ISSN: 1091-6490 [Electronic] United States
• PMID: 24194549 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Munc18 Proteins
• Qa-SNARE Proteins
• STX11 protein, human
• STXBP2 protein, human

Topics

• Animals
• Blotting, Western
• Crystallization
• Evolution, Molecular
• HEK293 Cells
• Humans
• Immunohistochemistry
• Killer Cells, Natural (immunology, metabolism)
• Lymphohistiocytosis, Hemophagocytic (genetics)
• Models, Molecular
• Munc18 Proteins (chemistry, genetics, metabolism)
• Point Mutation (genetics)
• Protein Binding
• Qa-SNARE Proteins (metabolism)
• Sf9 Cells
• Spodoptera
• T-Lymphocytes, Cytotoxic (immunology, metabolism)