The Co-crystal structure of staphylococcal enterotoxin type A with Zn2+ at 2.7 A resolution. Implications for major histocompatibility complex class II binding - PubMed (original) (raw)

. 1996 Dec 13;271(50):32212-6.

doi: 10.1074/jbc.271.50.32212.

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The Co-crystal structure of staphylococcal enterotoxin type A with Zn2+ at 2.7 A resolution. Implications for major histocompatibility complex class II binding

M Sundström et al. J Biol Chem. 1996.

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Abstract

Superantigens form complexes with major histocompatibility complex (MHC) class II molecules and T-cell receptors resulting in extremely strong immunostimulatory properties. Staphylococcus aureus enterotoxin A (SEA) belongs to a subgroup of the staphylococcal superantigens that utilizes Zn2+ in the high affinity interaction with MHC class II molecules. A high affinity metal binding site was described previously in SEA co-crystallized with Cd2+ in which the metal ion was octahedrally co-ordinated, involving the N-terminal serine. We have now co-crystallized SEA with its native co-factor Zn2+ and determined its crystal structure at 2.7 A resolution. As expected for a Zn2+ ion, the co-ordination was found to be tetrahedral. Three of the ligands are located on the SEA surface on a C-terminal domain beta-sheet, while the fourth varies with the conditions. Further analysis of the zinc binding event was performed using titration microcalorimetry, which showed that SEA binds Zn2+ with an affinity of KD = 0.3 microM in an entropy driven process. The differential Zn2+ co-ordination observed here has implications for the mechanism of the SEA-MHC class II interaction.

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