Investigating polymeric antibody assembly, structure, function and therapeutic potential

本研究旨在探讨聚合物（p）的组装机制、结构和功能 免疫球蛋白（IG），其填充粘膜。猪免疫球蛋白存在于脊椎动物中， 不同的抗体。它们包含几种IG重链类别，包括哺乳动物伊加和IgM， 其通常含有两个和五个之间的IG单体和一个连接链（JC）;然而， 与JC组装和/或组装成不同大小的聚合物随脊椎动物物种和IG而变化 重链类。组装后，pIg通过多聚IG受体（pIgR）转运至粘膜。 在粘膜中，称为分泌组分（SC）的pIgR胞外结构域保持结合，并且复合物被 称为分泌型（S）IG。SIgA是哺乳动物中的主要粘膜抗体;它通常在哺乳动物中发现。 二聚体（d）形式;然而更高级的聚合物如四聚体在功能上是相关的。SIgA与 与单体循环抗体相比，具有独特的效应器功能;它可以包被，交联和 凝集寄生虫和病原性抗原，还介导与宿主上的受体的相互作用， 微生物细胞尽管意义重大，但pIg组装和SIG功能的结构基础仍然很差。 通过几十年的免疫学研究才得以理解。到2020年， 发表了SIgM、SIgA和二聚体（d）伊加前体，揭示了前所未有的分子见解， 这些关键的复合物，并打开大门，以新的问题和结构引导的实验。的 dIgA和二聚体形式的SIgA的结构显示两个IgA通过JC连接形成假对称的， 弯曲构象，似乎限制抗原结合片段（Fab）的位置并促进进入 到受体结合位点。SC不对称地结合到一侧，并且是溶剂可接近的，这表明它 可能促进与宿主或微生物因子的尚未表征的相互作用。这些观察提出了 pIg之间的结构差异是如何产生的问题（例如，二聚体与四聚体和JC与无JC JC），组件的弯曲，不对称排列是如何诱导和维持的，以及它是如何贡献的 来运作。拟议的研究计划将使用结构和生物物理方法来针对这些 问题.目的1将鉴定IG重链残基、结构基序和/或构象变化， 促进pIg组装和控制pIg聚合状态，同时还决定JC-1的结构基础。 独立的pIg组装和功能。目的2将表征pIg组装的JC特异性机制， 它的结构贡献dIgA的假对称构象。目标3将描述功能 重要性SC及其结合微生物配体的能力。这些研究将提供全面的机制 用于pIg组装的模型，生成新的pIg结构并报告新的SIG结构-功能关系。这 这一结果将提高对粘膜免疫的认识，并为工程化pIg和SIG提供基础。 探讨其正常功能和治疗潜力。

This proposal aims to investigate the assembly mechanisms, structures, and functions of polymeric (p) immunoglobulins (Ig) that populate the mucosa. The pIgs are found in vertebrates and together form a structurally diverse group of antibodies. They comprise several Ig heavy chain classes, including mammalian IgA and IgM, which typically contain between two and five Ig monomers and one joining chain (JC); however, potential to assemble with the JC and/or to assemble into polymers of different size varies with vertebrate species and Ig heavy chain class. Following assembly, pIgs are transported to the mucosa by the polymeric Ig receptor (pIgR). In the mucosa, the pIgR ectodomain, called secretory component (SC), remains bound and the complex is referred to as a secretory (S) Ig. SIgA is the predominant mucosal antibody in mammals; it is typically found in dimeric (d) forms; however higher order polymers such as tetramers are functionally relevant. SIgA is associated with unique effector functions compared to monomeric, circulatory antibodies; it can coat, cross-link and agglutinate commensal and pathogenic antigens and also mediate interactions with receptors on host and microbial cells. Despite significance, the structural basis for pIg assembly and SIg functions remained poorly understood through decades of immunological research. In 2020 the cryo-electron microscopy structures of SIgM, SIgA and a dimeric (d) IgA precursor were published revealing unprecedented molecular insights into these crucial complexes and opening the door to new questions and structure-guided experiments. The structures of dIgA and dimeric forms of SIgA revealed two IgAs joined through the JC to form a pseudosymmetric, bent conformation that appears to restrict the positions of antigen-binding fragments (Fabs) and promote access to receptor-binding sites. The SC is asymmetrically bound to one side and is solvent accessible, suggesting it may promote yet uncharacterized interactions with host or microbial factors. These observations raise the questions of how structural differences among pIg are generated (e.g dimer versus tetramer and JC versus no JC), how the bent, asymmetric arrangement of components is induced and maintained, and how it contributes to function. The proposed research program will use structural and biophysical approaches to target these questions. Aim 1 will identify Ig heavy chain residues, structural motifs and/or conformational changes that promote pIg assembly and control pIg polymeric state, while also determining the structural basis for JC- independent pIg assembly and function. Aim 2 will characterize JC-specific mechanisms of pIg assembly and its structural contributions to the pseudosymmetric conformation of dIgA. Aim 3 will characterize the functional significance SC and its capacity to bind microbial ligands. These studies will deliver comprehensive mechanistic models for pIg assembly, generate new pIg structures and report new SIg structure-function relationships. This outcome will improve knowledge of mucosal immunity and provide a foundation for engineering pIg and SIg in order to explore their normal functions and therapeutic potential.