Molecular Evolution of Podocyte Slit-diaphragm Proteins

Vertebrates kidneys contribute to the homeostasis by regulating electrolyte, acid-base balance, and prevent protein loss into the urine. Glomerular podocytes constitute blood-urine barrier and podocyte slit-diaphragm, a modified tight junction contributes to the glomerular permselectivity. Nephrin, podocin, CD2AP, and TRPC6 are considered to be crucial members, which largely interact with each other and contribute to the structural and functional integrity of the slit-diaphragm. In this study, we analyzed the distribution of these four-key slit-diaphragm proteins across the organisms for which the genome sequence is available. We found that nephrin has a diverse distribution ranging from nematodes to higher vertebrates whereas podocin, CD2AP, and TRPC6 are predominantly restricted to the vertebrates. In the invertebrates nephrin and its orthologs consist of more immunoglobulin-3 and immunoglobulin-5 domains when compared to the vertebrates wherein, CD80-like C2-set Ig2 domains were predominant. Src Homology-3 (SH3) domain of CD2AP and SPFH domain of podocin are highly conserved among vertebrates. Although the majority of the TRPC6 and its orthologs had conserved ankyrin repeats, TRP, and ion transport domains, the orthologs of TRPC6 present in Rhincodon typus and Acanthaster planci do not possess the ankyrin repeats. Intrinsically unstructured regions (IURs), which are considered to contribute to the interactions among these proteins are largely conserved among orthologs of these proteins, suggesting the importance of IURs in the protein complexes that constitute slit-diaphragm. This study for the first time reports the evolutionary insights of vertebrate slit-diaphragm proteins and its invertebrate orthologs.