The Peptidyl Prolyl Isomerases CG10907 and Cyp1 modulate VAPB folding

Abstract

Amyotrophic Lateral Sclerosis (ALS) is a lethal neurodegenerative disease characterized by the loss of motor neurons, leading to paralysis and death of the patient. Most cases are sporadic, while 10% of cases are familial. At least 18 genes have been identified as definitive loci to cause ALS. VAMP-Associated Protein B (VAPB) is the 8th locus discovered with a Proline to Serine mutation at the 56th position that can cause fALS. VAPB is an ER membrane protein that acts as a docking site for various proteins that bind to its MSP (Major Sperm Protein) Domain. VAPB (referred to as VAP hereafter) is thus involved in multiple contact site-specific functions, including vesicle fission, membrane trafficking, lipid transport regulation, etc. Our lab has generated an orthologous mutation (P58S) in Drosophila using genome-based CRISPR-Cas9 editing, which exhibits ALS8-like phenotypes, including motor and lifespan defects, ER stress, inflammation, and perturbed lipid metabolism. VAPP58S aggregation in neurons is a distinctive feature of the ALS8 neurodegeneration model. Proline residues are unique in that they can stably exist in both cis and trans conformations, and this isomerization is intrinsically slow and rate-limiting. In the VAP-MSP domain, of the total 7 Prolines, 3 are in cis conformation. Since the conserved proline at position 58 is in the cis conformation, whereas the substitution with serine forces a trans conformation, we investigated whether the loss of cis conformation contributes to the observed misfolded protein aggregation. Preliminary studies suggest that loss of cis conformation leads to insoluble aggregates. We further attempted to shift the aggregation kinetics of the VAP protein by targeting a family of proteins called Peptidyl Prolyl isomerases (PPIases). PPIases are a superfamily of chaperones that help in proline cis-trans isomerisation. Our study identified specific PPIases, such as CG10907 and Cyp1, that contributed to modifying aggregates and their various parameters, thereby helping us suggest the underlying mechanism of disease progression.