The Crystal Structure of the Michaelis-Menten Complex of C1 Esterase Inhibitor and C1s Reveals Novel Insights into Complement Regulation.

IF 3.6 3区 医学 Q2 IMMUNOLOGY
Ryan J Garrigues, Matthew P Garrison, Brandon L Garcia
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引用次数: 0

Abstract

The ancient arm of innate immunity known as the complement system is a blood proteolytic cascade involving dozens of membrane-bound and solution-phase components. Although many of these components serve as regulatory molecules to facilitate controlled activation of the cascade, C1 esterase inhibitor (C1-INH) is the sole canonical complement regulator belonging to a superfamily of covalent inhibitors known as serine protease inhibitors (SERPINs). In addition to its namesake role in complement regulation, C1-INH also regulates proteases of the coagulation, fibrinolysis, and contact pathways. Despite this, the structural basis for C1-INH recognition of its target proteases has remained elusive. In this study, we present the crystal structure of the Michaelis-Menten (M-M) complex of the catalytic domain of complement component C1s and the SERPIN domain of C1-INH at a limiting resolution of 3.94 Å. Analysis of the structure revealed that nearly half of the protein/protein interface is formed by residues outside of the C1-INH reactive center loop. The contribution of these residues to the affinity of the M-M complex was validated by site-directed mutagenesis using surface plasmon resonance. Parallel analysis confirmed that C1-INH-interfacing residues on C1s surface loops distal from the active site also drive affinity of the M-M complex. Detailed structural comparisons revealed differences in substrate recognition by C1s compared with C1-INH recognition and highlight the importance of exosite interactions across broader SERPIN/protease systems. Collectively, this study improves our understanding of how C1-INH regulates the classical pathway of complement, and it sheds new light on how SERPINs recognize their cognate protease targets.

C1 酯酶抑制剂和 C1s 的 Michaelis-Menten 复合物晶体结构揭示了补体调节的新观点。
被称为补体系统的先天免疫系统是一种血液蛋白水解级联,涉及数十种膜结合和溶液相成分。尽管这些成分中有许多是促进级联激活的调节分子,但 C1 酯酶抑制剂(C1-INH)是唯一的典型补体调节剂,属于被称为丝氨酸蛋白酶抑制剂(SERPINs)的共价抑制剂超家族。除了它在补体调节中的同名作用外,C1-INH 还能调节凝血、纤维蛋白溶解和接触途径中的蛋白酶。尽管如此,C1-INH 识别其目标蛋白酶的结构基础仍然难以捉摸。在这项研究中,我们以 3.94 Å 的极限分辨率展示了补体成分 C1s 催化结构域与 C1-INH 的 SERPIN 结构域的 Michaelis-Menten (M-M) 复合物晶体结构。这些残基对 M-M 复合物亲和力的贡献通过使用表面等离子共振的定点突变得到了验证。平行分析证实,远离活性位点的 C1s 表面环上的 C1-INH 干扰残基也会驱动 M-M 复合物的亲和力。详细的结构比较揭示了 C1s 对底物的识别与 C1-INH 识别之间的差异,并强调了在更广泛的 SERPIN/蛋白酶系统中外物相互作用的重要性。总之,这项研究加深了我们对 C1-INH 如何调控补体的经典途径的理解,并对 SERPIN 如何识别其同源蛋白酶靶标提供了新的启示。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of immunology
Journal of immunology 医学-免疫学
CiteScore
8.20
自引率
2.30%
发文量
495
审稿时长
1 months
期刊介绍: The JI publishes novel, peer-reviewed findings in all areas of experimental immunology, including innate and adaptive immunity, inflammation, host defense, clinical immunology, autoimmunity and more. Special sections include Cutting Edge articles, Brief Reviews and Pillars of Immunology. The JI is published by The American Association of Immunologists (AAI)
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