Antigenically sequence variable M proteins of the major bacterial pathogen (Strep A) are responsible for recruiting human C4b-binding protein (C4BP) to the bacterial surface, which enables Strep A to evade destruction by the immune system. The most sequence divergent portion of M proteins, the hypervariable region (HVR), is responsible for binding C4BP. Structural evidence points to the conservation of two C4BP-binding sequence patterns (M2 and M22) in the HVR of numerous M proteins, with this conservation applicable to vaccine immunogen design. These two patterns, however, only partially explain C4BP binding by Strep A. Here, we identified several M proteins that lack these patterns but still bind C4BP and determined the structures of two, M68 and M87 HVRs, in complex with a C4BP fragment. Mutagenesis of these M proteins led to the identification of amino acids that are crucial for C4BP binding, enabling formulation of new C4BP-binding patterns. Mutagenesis was also carried out on M2 and M22 proteins to refine or generate experimentally grounded C4BP-binding patterns. The M22 pattern was the most prevalent among M proteins, followed by the M87 and M2 patterns, while the M68 pattern was rare. These patterns, except for M68, were also evident in numerous M-like Enn proteins. Binding of C4BP these patterns to Enn proteins was verified. We conclude that C4BP-binding patterns occur frequently in Strep A strains of differing M types, being present in their M or Enn proteins, or frequently both, providing further impetus for their use as vaccine immunogens.

中文翻译：

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化脓性链球菌 M 和 Enn 蛋白中 C4BP 结合序列模式的保守性


主要细菌病原体 (Strep A) 的抗原序列可变 M 蛋白负责将人类 C4b 结合蛋白 (C4BP) 募集到细菌表面，从而使 Strep A 能够逃避免疫系统的破坏。 M 蛋白序列差异最大的部分，即高变区 (HVR)，负责结合 C4BP。结构证据表明，许多 M 蛋白的 HVR 中存在两种 C4BP 结合序列模式（M2 和 M22）的保守性，这种保守性适用于疫苗免疫原设计。然而，这两种模式只能部分解释链球菌 A 与 C4BP 的结合。在这里，我们鉴定了几种缺乏这些模式但仍结合 C4BP 的 M 蛋白，并确定了与 C4BP 片段复合的两种 HVR（M68 和 M87 HVR）的结构。这些 M 蛋白的诱变导致了对 C4BP 结合至关重要的氨基酸的鉴定，从而能够制定新的 C4BP 结合模式。还对 M2 和 M22 蛋白进行了诱变，以改进或生成基于实验的 C4BP 结合模式。 M22 模式在 M 蛋白中最常见，其次是 M87 和 M2 模式，而 M68 模式则很少见。除 M68 外，这些模式在许多 M 样 Enn 蛋白中也很明显。 C4BP 这些模式与 Enn 蛋白的结合得到了验证。我们得出的结论是，C4BP 结合模式经常出现在不同 M 类型的 A 链球菌菌株中，存在于其 M 或 Enn 蛋白中，或经常同时存在于两者中，这为它们用作疫苗免疫原提供了进一步的动力。