Structural Features and Oligomeric Nature of Human Podocin Domain

Abstract

Podocytes are crucial cells of the glomerular filtration unit and playing a vital role at the interface of the blood-urine barrier. Podocyte slit-diaphragm is a modified tight junction that facilitates size and shape-dependent permselectivity. Several proteins including podocin, nephrin, CD2AP, and TRPC6 form a macromolecular assembly and constitute the slit-diaphragm. Podocin is an integral membrane protein attached to the inner membrane of the podocyte via a short transmembrane region (101-125). The cytosolic N-and C-terminus help podocin to attain a hooklike structure. Podocin shares 44% homology with stomatin family proteins and similar to the stomatin proteins, podocin was shown to associate into higher-order oligomers at the site of slitdiaphragm. However, the stoichiometry of the homo-oligomers and how it partakes in the macromolecular assemblies with other slit-diaphragm proteins remains elusive. Here we investigated the oligomeric propensity of a truncated podocin construct (residues:126-350). We show that the podocin domain majorly homo-oligomerize into a 16mer. Circular dichroism and fluorescence spectroscopy suggest that the 16mer oligomer has considerable secondary structure and moderate tertiary packing.

Molecular Evolution of Podocyte Slit-diaphragm Proteins

“…IURs are conserved motifs in SD proteins and its orthologs: SD proteins are known to form large complexes via homo-and heterophilic interactions which are believed to be mediated by IURs [2,6,15]. Since the SD proteins and its orthologs share similar domains and appreciable sequence similarity, we investigated if IUR motifs are conserved in the SD proteins and its orthologs.…”

“…Podocin acts as a scaffolding molecule and provides structural integrity to the SD by forming a macromolecular complex with nephrin, CD2AP, TRPC6, and KIRREL1 [9,33]. It was reported that besides forming a heteromeric complex, podocin like its family members associates into higher order oligomers [6,34]. It is suggested the that the numerous interactions formed by podocin with its client proteins may be attributed to the podocin's oligomeric nature since, each molecule in the podocin homo-oligomer can interact with one of its client proteins [15].…”

“…Altered podocyte morphology (effacement) leads to excess proteinuria, hypoalbuminemia, and edema which are hallmark symptoms of nephrotic syndrome (NS) [6]. Corticoid therapy is the usual recourse to abate NS.…”