The crystal structure of staphylococcal enterotoxin H: Implications for binding properties to MHC class II and TcR molecules

M. Håkansson, Karin Lindkvist, H. Nilsson, G Forsberg, P. Björk, Per Antonsson, Liz Svensson

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The X-ray structure of the superantigen staphylococcal enterotoxin H (SEH) has been determined at 1.69 Å resolution. In this paper we present two structures of zinc-free SEH (apoSEH) and one zinc-loaded form of SEH (ZnSEH). SEH exhibits the conventional superantigen (SAg) fold with two characteristic domains. In ZnSEH one zinc ion per SEH molecule is bound to the C-terminal β-sheet in the region implicated for major histocompatibility complex class II (MHC class II) binding in SEA, SED and SEE. Surprisingly, the zinc ion has only two ligating amino acid residues His206 and Asp208. The other ligands to the zinc ion are two water molecules. An extensive packing interaction between two symmetry-related molecules in the crystal, 834 Å2/molecule, forms a cavity that buries the zinc ions of the molecules. This dimer-like interaction is found in two crystal forms. Nevertheless, zinc-dependent dimerisation is not observed in solution, as seen in the case of SED. A unique feature of SEH as compared to other staphylococcal enterotoxins is a large negatively charged surface close to the Zn2+ site. The interaction of SEH with MHC class II is the strongest known among the staphylococcal enterotoxins. However, SEH seems to lack a SEB-like MHC class II binding site, since the side-chain properties of structurally equivalent amino acid residues in SEH and those in SEB-binding MHC class II differ dramatically. There is also a structural flexibility between the domains of SEH. The domains of two apoSEH structures are related by a 5°rotation leading to at most 3 Å difference in C(α) positions. Since the T-cell receptor probably interacts with both domains, SEH by this rotation may modulate its binding to different TcR Vβ-chains. (C) 2000 Academic Press.

Original languageEnglish
Pages (from-to)527-537
Number of pages11
JournalJournal of Molecular Biology
Issue number3
Publication statusPublished - 2000 Sep 22

Subject classification (UKÄ)

  • Cell and Molecular Biology


  • MHC class II
  • SEH
  • Structure
  • Superantigen
  • Zinc binding


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