Robin Maser (2015-2016)
Associate Professor, Department of Clinical Laboratory Sciences
University of Kansas Medical Center

Heterotrimeric G Protein Binding by Polycystin-1, an Atypcial GPCR

By elucidating the sequence elements and characteristics of PC1 that are involved in the selection and binding of heterotrimeric G proteins, this proposal will potentially provide new and important information for understanding the mechanism of PC1-mediated G protein signaling and its putative role in ADPKD.

Mutation of the PKD1 gene is the primary cause of autosomal dominant polycystic kidney disease (ADPKD), which is the fourth leading cause of chronic kidney disease. Currently, there is no approved clinical therapy for ADPKD in the US. PKD1 encodes polycystin-1 (PC-1), an integral membrane protein of >4,300 residues with 11 transmembrane (TM) segments and a short, C-terminal cytosolic tail. In vitro and cell culture-based assays have demonstrated an ability of the PC1 C-tail to bind and to activate heterotrimeric G protein signaling, which appears to be mediated via a highly conserved, 20-residue sequence, the G protein activation motif. A number of ADPKD-associated mutations have been identified in, or adjacent to, this motif. The pathogenic significance of such mutations was revealed when Pkd1ΔL/ΔL mice, with a knock-in of one
of these ADPKD mutations, were shown to develop polycystic kidneys in utero and die while embryos.These recent results strongly support the view that this region of the PC1 C-tail, and most likely G proteinmediated signaling, is critical for the function of PC1 in preventing cystic kidney development.

The overall goal of this research is to understand the relationship between PC1 function and structure, and how it contributes to the development of ADPKD. Deciphering the mechanism of PC1-mediated G protein signaling, its regulation, and how PKD1 mutations within this region of the C-tail result in cystic disease will require understanding the basis of PC1-G protein interaction. Recent work supports the hypothesis that membrane-associated portions, in addition to the cytosolic C-tail, contribute to the regulation of PC1-mediated G protein signaling. The goal of this proposal is to define the basis for selective binding of G alpha subunits (Gα) by the PC1 C-tail. These studies will utilize surface plasmon resonance (SPR) to determine the binding selectivity and affinity between the PC1 C-tail and different Gα subunits, and will identify the determinants of the C-tail involved.