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

ABSTRACT

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.

KEYWORDS:

• Podocyte
• nephrotic syndrome
• slit-diaphragm
• protein–protein interactions
• intrinsically disordered regions

Acknowledgements

We thank the SERB, India for providing research grants (EMR/2015/002076 to AKP and also to Indian council of medical research (3/1/2(4)/Nephro/2015/NCD-II) for providing fellowship to Mulukala NSK. We acknowledge the resources provided by Biotechnology Infrastructure Facility of the University of Hyderabad and also the structural biology laboratory at BITS-Pilani Hyderabad.

Disclosure Statement

No potential conflict of interest was reported by the authors.

Conflict of Interest

The authors declare no conflicts of interest.

Additional information

Funding

This work was supported by Indian Council of Medical Research: [Grant Number 3/1/2(4)/Nephro/2015/NCD-II]; Science and Engineering Research Board: [Grant Number EMR/2015/002076].