Grossman D, Van M, Mollick J A, Highlander S K, Rich R R
Department of Microbiology, Baylor College of Medicine, Houston, TX 77030.
J Immunol. 1991 Nov 15;147(10):3274-81.
The hallmark of T cell responses to staphylococcal enterotoxins (SE) and other super-Ag is a selective stimulation of cells expressing particular TCR-V beta segments. Our previous studies suggested that the disulfide loop in SE is critical for their interaction with the TCR. To investigate this concept in further detail we constructed disulfide loop mutants of staphylococcal enterotoxin A (SEA), and examined these altered toxins for mitogenicity, class II MHC binding, and V beta specificity. We found that substitutions of either Cys-96 or Cys-106 decreased mitogenicity by 100-fold without significantly affecting class II binding or resistance of the molecule to proteolysis. Several mutants lost the capacity to stimulate V beta 11+ cells, except a Cys-106----Gln mutant for which V beta 11-stimulatory activity was increased. By contrast, mutants containing Cys----Ala substitutions acquired the capacity to stimulate V beta 6+ cells. Despite these effects of V beta specificity, all mutants retained the predominant preference of SEA for V beta 3+ cells. Neither exchange of regions flanking the loop in SEA with corresponding residues in SEB, nor conversion of the entire loop region of SEA to that of SEE, were associated with transfers of V beta specificity. Our results suggest that the disulfide loop in SEA contributes to toxin avidity for the TCR, rather than specificity for particular V beta.
T细胞对葡萄球菌肠毒素（SE）和其他超抗原的反应的标志是对表达特定TCR-Vβ片段的细胞的选择性刺激。我们之前的研究表明，SE中的二硫键环对于它们与TCR的相互作用至关重要。为了更详细地研究这一概念，我们构建了葡萄球菌肠毒素A（SEA）的二硫键环突变体，并检测这些改变的毒素的促有丝分裂活性、II类MHC结合以及Vβ特异性。我们发现，Cys-96或Cys-106的取代使促有丝分裂活性降低了100倍，而对II类结合或分子对蛋白水解的抗性没有显著影响。几个突变体失去了刺激Vβ11+细胞的能力，除了一个Cys-106→Gln突变体，其Vβ11刺激活性增加。相比之下，含有Cys→Ala取代的突变体获得了刺激Vβ6+细胞的能力。尽管有这些Vβ特异性的影响，所有突变体都保留了SEA对Vβ3+细胞的主要偏好。SEA中环两侧区域与SEB中相应残基的交换，以及SEA整个环区域向SEE环区域的转化，均与Vβ特异性的转移无关。我们的结果表明，SEA中的二硫键环有助于毒素对TCR的亲和力，而不是对特定Vβ的特异性。
