Structural and Functional Roles of Transmembrane Domains in B-cell Receptor Signalling

b细胞受体（BCR）复合物由抗原结合亚基（膜免疫球蛋白，mIg）和信号传导亚基（CD79a-b异源二聚体）组成，是人类最重要的免疫受体之一，控制着b细胞的发育、活性、选择和死亡。然而，BCR信号传导的机制仍然是一个猜测问题，部分原因是缺乏原子水平的结构数据，这些数据揭示了复合物中对功能性受体组装、运输和信号传递至关重要的区域，即跨膜结构域（TMDs）。我们假设BCR复合体中三种蛋白质的tmd是强而特异性（尚未表征）相互作用的介质，并概述了将首次产生BCR tmd结构和相互作用的分子水平描述的工作。我们的假设是基于25年前的报道，这些报道暗示TM结构域是功能必需的蛋白质-蛋白质和蛋白质-脂质相互作用的位点，但到目前为止还没有揭示出对这一作用的分子水平的理解。本提案概述了BCR tmd的结构和相互作用的分子水平，生物物理研究，我们将使用这些研究来设计分子来调节BCR功能。具体来说，我们将(i)描述天然膜中BCR复合物组分内部和组分之间TMD相互作用的强度和序列依赖性，（ii）利用一组生物物理方法来描述多种（合成）脂质环境中TMD相互作用的结构、稳定性、化学计量学和原子细节，以及（iii）使用这些新信息来设计和测试分子破坏相互作用和修改BCR信号传导和原位功能的能力。这项工作将产生BCR tmd之间相互作用的第一张地图，以及不同脂质环境下BCR tmd的第一个结构数据，从而增强我们对BCR信号传导的机制理解，并支持基础免疫学的研究。我们设计的分子将作为BCR调节的概念证明，使用这种方法是可能的，并为未来更全面的药物发现计划提供一个平台，用于自身免疫性疾病、b细胞白血病和淋巴瘤的新治疗方法。

The B-cell receptor (BCR) complex, comprised of an antigen-binding subunit (membrane immunoglobulin, mIg) and a signalling subunit (the CD79a-b heterodimer), is one of the most important immune receptors in humans and controls B-cell development, activity, selection and death. Yet the mechanism of BCR signalling remains a matter of speculation, partly because of a lack of atomic-level structural data that reveals regions of the complex critical for functional receptor assembly, transport, and signal transmission, namely the transmembrane domains (TMDs). We hypothesise that the TMDs of the three proteins in the BCR complex are mediators of strong and specific (yet uncharacterised) interactions, and outline here work that would yield a molecular-level description of the structures and interactions of the BCR TMDs for the first time. Our hypothesis is based on reports dating back over 25 years which implicate the TM domains as sites of functionally essential protein-protein and protein-lipid interactions, but have thus far not revealed a molecular level understanding of this role. This proposal outlines a molecular-level, biophysical investigation of the structures and interactions of the BCR TMDs, which we will use to design molecules to modulate BCR function. Specifically, we will (i) characterise the strength and sequence dependence of TMD interactions within and between components of the BCR complex in a natural membrane, (ii) utilise a panel of biophysical methods to characterise the structure, stability, stoichiometry and atomic details of TMD interactions in multiple (synthetic) lipid environments, and (iii) use this new information to design and test ability of molecules to disrupt interactions and modify BCR signalling and function in situ. This work will yield the first map of interactions between the BCR TMDs and the first structural data for the BCR TMDs in different lipid environments, thus enhancing our mechanistic understanding of BCR signalling and supporting efforts in basic immunology. The molecules we design would act as a proof of concept that BCR modulation is possible using this approach, and provide a platform for a more comprehensive drug discovery programme in the future towards new theraputic treatments for autoimmune diseases, B-cell leukaemias and lymphomas.