Structural and Molecular Mechanisms for Dysregulation of Protein Kinase C Gamma in Cerebellar Ataxia

Summary/Abstract The overall vision of our proposed research is to understand the structural, molecular, and cellular mechanisms by which germline mutations in protein kinase C gamma (PKCg) drive the neuro- degenerative disease Spinocerebellar Ataxia 14 (SCA14). PKCg is a Ca2+/diacylglycerol-regulated kinase expressed only in neurons, including Purkinje cells whose degeneration is a hallmark of the almost 50 subtypes of SCA. We have assembled a team with extensive and complementary expertise in structural biology of kinases and in PKC mechanisms to understand how these mutations alter the structure and function of PKCg to contribute to the disease phenotype. The hypothesis driving this proposal is that mutations are concentrated at specific regions of PKCg that break autoinhibitory contacts to enhance its activity by a novel mechanism that evades normal quality control degradation. This evasion of degradation may be a unique feature of the Ataxia mutations as cancer-associated mutations that break autoinhibitory contacts destabilize PKC and shunt it to degradation. Such evasion of normal quality control allows aberrantly active PKCg to enhance its signaling output, which in Purkinje cells in the cerebellum leads to degeneration. Furthermore, we hypothesize that enhanced signaling by PKCg may underlie the pathology of SCA, in general, as a large fraction of SCAs are caused by mutations in proteins that control Ca2+ homeostasis or signaling. We aim to combine computational, structural, biochemical, live-cell imaging, and phosphoproteomics approaches to understand the molecular details of how disease-associated mutations in PKCg impact function, with the long-term future goal of using this knowledge to treat this devastating disease.