Intrinsically disordered regions mediate macromolecular assembly of the Slit diaphragm proteins associated with Nephrotic syndrome

The glomerular filtration barrier (GFB) of the kidney plays an instrumental role in preventing the excretion of large molecules and ensuring the formation of ultra-filtrated urine. Podocytes are essential components of GFB that provide epithelial coverage to the fine glomerular capillaries. Slit-diaphragm (SD) that forms the sole contact between adjacent foot-processes of the podocytes consists of multimeric protein assemblies. SD serves as a molecular sieve and confers size and charge-selective barrier. Nephrin, podocin, TRPC6, and CD2AP are some of the key proteins that constitute the SD. Mutations in these proteins are implicated in nephrotic syndrome and congenital nephropathies which are characterised by heavy proteinuria. The mechanism of how mutations in these proteins predispose to proteinuria is not known. Furthermore, the structural details of proteins that constitute SD are largely unknown. In this study, we built models for nephrin, CD2AP, podocin, and TRPC6 followed by docking and molecular dynamics simulations of the complex of these proteins. We speculate that the interfacial residues of SD proteins form a macromolecular complex through intrinsically disordered regions thereby conferring architectural stability to the SD, which is critical for glomerular permselectivity.肾脏的肾小球滤过屏障（glomerular filtration barrier, GFB）在阻止大分子物质排泄、保障超滤尿液形成方面发挥关键作用。足细胞（Podocytes）是GFB的核心组成成分，可为纤细的肾小球毛细血管提供上皮被覆。裂孔隔膜（SD）作为相邻足细胞足突间唯一的接触结构，由多聚蛋白复合物组装而成。SD作为分子筛，赋予滤过屏障尺寸选择性与电荷选择性。肾病蛋白（Nephrin）、足蛋白（Podocin）、TRPC6以及CD2AP是构成SD的关键蛋白。上述蛋白的突变与以重度蛋白尿为特征的肾病综合征及先天性肾病密切相关。目前，此类蛋白突变诱发蛋白尿的具体机制尚未明确，且构成SD的蛋白的结构细节也尚未被充分阐明。本研究中，我们首先构建了肾病蛋白（Nephrin）、CD2AP、足蛋白（Podocin）以及TRPC6的结构模型，随后对这些蛋白组成的复合物开展了分子对接与分子动力学模拟。我们推测，SD蛋白的界面残基可通过内在无序区域形成大分子复合物，进而为SD赋予结构稳定性，这对于肾小球的选择性滤过功能至关重要。