Superantigen natural affinity maturation revealed by the crystal structure of staphylococcal enterotoxin g and its binding to T-cell receptor vβ8.2
Superantigen natural affinity maturation revealed by the crystal structure of staphylococcal enterotoxin g and its binding to T-cell receptor vβ8.2
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DOI：
10.1002/prot.21388
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发表时间：
2007-07-01
影响因子：
2.9
通讯作者：
Malchiodi, Emilio L.
中科院分区：
文献类型：
--
作者：
Fernandez, Marisa M.;Bhattacharya, Suparna;Malchiodi, Emilio L.
与细菌超抗原(SAG)有关的疾病，如食物中毒和中毒性休克综合征，以及新出现的暴发性紫癜和社区相关的耐甲氧西林金黄色葡萄球菌生产SAG的威胁，强调了更好地表征SAG与其天然配体结合的重要性，这将使能够中和其作用的药物或生物试剂的开发成为可能。SAGS是一种毒素，以非常规方式结合主要组织相容性复合体II类分子(MHC-II)和T细胞受体(TCR)，诱导T细胞激活，导致肿瘤坏死因子和白介素2等细胞因子的产生，从而可能导致急性中毒性休克。此前，我们克隆并表达了葡萄球菌肠毒素G(SEG)的一个新的天然变体，并评价了其在体内刺激小鼠T细胞亚群的能力。我们发现，与SEB亚家族的其他SAGS成员相比，小鼠Vβ8.2 T细胞具有早期、强烈和广泛的刺激作用。为了寻找有丝分裂能力强的原因，我们用2.2埃分辨率的X射线结晶学测定了SEG的晶体结构，并分析了SEG与MVβ8.2和MHC-II的结合。量热法和SPR分析表明，SEG对MVβ8.2的亲和力比SEB亚家族其他成员的亲和力高40~100倍，其中野生型SAG-TCR的亲和力最高。我们还发现，MV Beta 8.2中引入的突变产生了与SEB亚家族其他成员的高亲和力突变体，但不会对SEG的结合产生很大影响。结晶学分析和与SEB、SEC3和SPEA形成的复合物与MVβ8.2的对接表明，关键氨基酸的缺失和取代改变了MVβ8.2结合部位的表面，而不影响与MHC-II的结合。这导致了SAG与其天然配体结合的改善，这可能为表达SEG的细菌菌株提供可能的进化优势。
The illnesses associated with bacterial superantigens (SAgs) such as food poisoning and toxic shock syndrome, as well as the emerging threat of purpura fulminans and community-associated methicillin-resistant S. aureus producer of SAgs, emphasize the importance of a better characterization of SAg binding to their natural ligands, which would allow the development of drugs or biological reagents able to neutralize their action. SAgs are toxins that bind major histocompatibility complex class II molecules (MHC-II) and T-cell receptors (TCR), in a nonconventional manner, inducing T-cell activation that leads to production of cytokines such as tumor necrosis factor and interleukin-2, which may result in acute toxic shock. Previously, we cloned and expressed a new natural variant of staphylococcal enterotoxin G (SEG) and evaluated its ability to stimulate in vivo murine T-cell subpopulations. We found an early, strong, and widespread stimulation of mouse V beta 8.2 T-cells when compared with other SAgs member of the SEB subfamily. In search for the reason of the strong mitogenic potency, we determined the SEG crystal structure by X-ray crystallography to 2.2 angstrom resolution and analyzed SEG binding to mV beta 8.2 and MHC-II. Calorimetry and SPR analysis showed that SEG has an affinity for mV beta 8.2 40 to 100-fold higher than that reported for other members of SEB subfamily, and the highest reported for a wild type SAg-TCR couple. We also found that mutations introduced in mV beta 8.2 to produce a high affinity mutant for other members of the SEB subfamily do not greatly affect binding to SEG. Crystallographic analysis and docking into mV beta 8.2 in complex with SEB, SEC3, and SPEA showed that the deletions and substitution of key amino acids remodeled the putative surface of the mV beta 8.2 binding site without affecting the binding to MHC-II. This results in a SAg with improved binding to its natural ligands, which may confer a possible evolutionary advantage for bacterial strains expressing SEG.