Science2014-06-12 3:35 PM

转移抗体“注意力”的蛋白可帮助病原体 A Structurally Distinct Human Mycoplasma Protein that Generically Blocks Antigen-Antibody Union

论文摘要 

一项新的研究显示,通过与其遭遇的抗体结合及迷惑所有抗体中的大多数,一种新发现的蛋白可阻止抗体行使其职能。这种被称作蛋白M的蛋白质的活性代表了细菌躲避免疫系统的一种新方式。蛋白M的可与无数抗体结合的能力还使它成为一种重要的用于工业规模抗体纯化的可能的工具。抗体是由免疫系统用来发现并中和像细菌及病毒等异物的大分子蛋白。大多数抗体会与特定的抗原结合。然而,在研究作为慢性感染基础的细胞过程时,Rajesh Grover及其同事发现了一种由支原体菌产生的能与许多不同抗体结合的独特的膜蛋白,其有效地掩盖了它们用于锁定抗原的分子空间。通过一系列的实验,研究人员显示,蛋白M会强力地与人、小鼠、大鼠、兔子、山羊及牛的抗体结合,从而降低了抗体与它们预期的病原体的结合能力。他们认为,蛋白M的大号尺寸(它看来是迄今发现的最大的抗体结合蛋白)可帮助它达到这一阻挡抗体的效应。而且正如其他的抗体结合蛋白曾经帮助科学家们提纯抗体以用于各种研究一样,这一蛋白也很可能会提供这样的帮助。

Abstract 

We report the discovery of a broadly reactive antibody-binding protein (Protein M) from human mycoplasma. The crystal structure of the ectodomain of transmembrane Protein M differs from other known protein structures, as does its mechanism of antibody binding. Protein M binds with high affinity to all types of human and nonhuman immunoglobulin G, predominantly through attachment to the conserved portions of the variable region of the κ and λ light chains. Protein M blocks antibody-antigen union, likely because of its large C-terminal domain extending over the antibody-combining site, blocking entry to large antigens. Similar to the other immunoglobulin-binding proteins such as Protein A, Protein M as well as its orthologs in other Mycoplasma species could become invaluable reagents in the antibody field.

Easy M

Our immune systems can produce a vastly diverse repertoire of antibody molecules that each recognize and bind to a specific foreign antigen via a hypervariable region. However, there are a few bacterial antigens—such as Protein A, Protein G, and Protein L—that instead bind to the antibody's conserved regions and can bind to a large number of different antibodies. These high-affinity broad-spectrum antibody-binding properties have been widely exploited both in the laboratory and in industry for purifying, immobilizing, and detecting antibodies. Grover et al. (p. 656) have now identified Protein M found on the surface of human mycoplasma, which displays even broader antibody-binding specificity. The crystal structure of Protein M revealed how Protein-M binding blocks the antibody's antigen binding site. This mechanism may be exploited by mycoplasma to escape the humoral immune response.

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