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Protein Science, Vol 5, Issue 8 1737-1741, Copyright © 1996 by Cold Spring Harbor Laboratory Press
FOR THE RECORD |
A. C. PAPAGEORGIOU, C. P. QUINN, D. BEER, R. D. BREHM, H. S. TRANTER, P. F. BONVENTRE and K. R. ACHARYA
School of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
Toxic shock syndrome toxin-1 (TSST-1) is one of a family of staphylococcal exotoxins recognized as microbial superantigens. The toxin plays a dominant role in the genesis of toxic shock in humans through a massive activation of the immune system. This potentially lethal illness occurs as a result of the interaction of TSST-1 with a significant proportion of the T-cell repertoire. TSST-1, like other superantigens, can bind directly to class II major histocompatibility (MHC class II) molecules prior to its interaction with entire families of V{beta} chains of the T-cell receptor (TCR). The three-dimensional structure of a mutant (His-135-Ala) TSST-1 was compared with the structure of the native (wild-type) TSST-1 at 2.5 A resolution. The replacement of His 135 of TSST-1 with an Ala residue results in the loss of T-cell mitogenicity and toxicity in experimental animals. This residue, postulated to be directly involved in the toxin-TCR interactions, is located on the major helix {alpha}2, which forms the backbone of the molecule and is exposed to the solvent. In the molecular structure of the mutant toxin, the helix {alpha}2 remains unaltered, but the His to Ala modification causes perturbations on the neighboring helix {alpha}1 by disrupting helix-helix interactions. Thus, the effects on TCR binding of the His 135 residue could actually be mediated, wholly or in part, by the {alpha}1 helix.
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