Evasion of host immunity by the M protein

A群链球菌（GAS，S.化脓性链球菌）仍然是主要的公共卫生威胁。这种广泛的克- 阳性细菌病原体引起急性侵袭性疾病并引起严重的自身免疫后遗症， 并在全球范围内造成发病率和死亡率。作为GAS的一个重要毒力因子， 抗原可变的M蛋白，使细菌能够逃避免疫调节吞噬杀伤 系统M蛋白通过募集特异性可溶性抗体， 将人蛋白质结合到GAS表面，其阻断主要调理素C3 b以及抗原- 特异性调理素抗体-即C4 b结合蛋白（C4 BP）、H因子（FH）和纤维蛋白原（Fg）。在 在某些GAS菌株中，M样蛋白发挥这一功能。已知的M类型超过220种，而大多数M 蛋白质类型结合C4 BP、FH或Fg，或这些的组合，在M中没有明显的共有结合基序， 这些人类蛋白质中的任何一种的M样蛋白质，除了最近由于我们的突破而对C4 BP的研究。这 是因为招募这些抗调理素人类蛋白的M蛋白的暴露部分， 序列变量虽然这些相互作用的抑制已显示使GAS对免疫应答敏感， 由于缺乏共识结合基序，阻碍了靶向这些基序的治疗目标 交互.我们最近的突破，报告在布法罗等人，为这个问题提供了一个解决方案。实际上我们 发现隐藏在许多M蛋白的可变区中的是一种三维（3D）模式， 是保守的结合C4 BP。M蛋白中的这种3D C4 BP结合模式是分散的（或隐藏的） 在可变氨基酸的海洋中，这使得3D模式几乎不可能通过初级识别 序列单独。然而，有了结构知识作为指导模板，3D图案变得 在许多M型的原始序列中很容易识别。我们假设就像C4 BP一样， 隐藏在M和M样蛋白的可变区中的是3D模式， 结合FH和Fg。我们建议通过以下方式来测试隐藏在变异中的保护这一新兴主题： 揭示了M和M样蛋白中潜在保守的FH和Fg结合3D模式。我们亦建议 完成我们对C4 BP的研究，因为我们发现并发表在布法罗等人的3D模式只解释了 涉及C4 BP结合的M蛋白组的大约一半。我们建议通过X射线来实现这一点 结晶学我们在M蛋白的晶体学研究方面有着广泛的成功记录， 已经获得了与C4 BP、FH和Fg结合的M蛋白的初始共晶体。在每一种情况下，我们将采取 利用我们的结构研究提供的高度详细的信息来确定精确的 这些相互作用中的每一种对毒力的功能贡献，通过我们与 共同研究员维克托尼泽特（加州大学圣地亚哥分校）。我们的研究结果将为设计提供必要的指导 抗毒力策略，并可能在广泛中和GAS疫苗的开发中具有应用。

Group A Streptococcus (GAS, S. pyogenes) remains a major public health threat. This widespread Gram- positive bacterial pathogen causes acute invasive diseases and gives rise to severe autoimmune sequelae, and is responsible for morbidity and mortality on a global scale. An essential virulence factor of GAS, the antigenically variable M protein, enables the bacterium to evade opsonophagocytic killing by the immune system. The M protein confers this indispensable function of phagocyte resistance by recruiting specific soluble human proteins to the GAS surface that block the deposition of the major opsonin C3b as well as antigen- specific opsonic antibodies — namely, C4b-binding protein (C4BP), factor H (FH), and fibrinogen (Fg). In some GAS strains, an M-like protein serves this function. More than 220 M types are known, and while most M protein types bind C4BP, FH, or Fg, or a combination of these, no consensus binding motif is evident in M and M-like proteins for any of these human proteins, except most recently for C4BP due to our breakthrough. This is because the exposed portion of the M protein that recruits these anti-opsonic human proteins is sequence variable. While inhibition of these interactions has been shown to render GAS sensitive to immune killing, the lack of consensus binding motifs has hindered the therapeutic goal of targeting these interactions. Our recent breakthrough, reported in Buffalo et al., offers a solution to this problem. In effect, we found that hidden within the variable region of many M proteins is a three-dimensional (3D) pattern that is conserved for binding C4BP. This 3D C4BP-binding pattern in the M protein is dispersed (or hidden) within a sea of variable amino acids, which makes the 3D pattern nearly impossible to identify by primary sequence alone. However with structural knowledge in hand as a guiding template, the 3D pattern becomes easily recognizable within the primary sequence of many M types. We hypothesize that just as with C4BP, hidden within the variable regions of M and M-like proteins are 3D patterns that are conserved for binding FH and Fg. We propose to test this emerging theme of conservation hidden within variability by unveiling potentially conserved FH- and Fg-binding 3D patterns in M and M-like proteins. We also propose to complete our work on C4BP, as the 3D pattern we discovered and published in Buffalo et al. explains only about a half of the set of M proteins implicated in C4BP binding. We propose to carry this out through X-ray crystallography. We have an extensive record of success with crystallographic studies of the M protein, and have obtained initial co-crystals of M proteins bound to C4BP, FH, and Fg. In each case, we will take advantage of the highly detailed level of information provided by our structural studies to determine the precise functional contributions of each of these interactions to virulence through our long-standing collaboration with co-Investigator Victor Nizet (UCSD). The results from our studies will provide essential guidance in designing anti-virulence strategies, and may have applications in the development of a broadly neutralizing GAS vaccine.