Dr. Manni Luthra Guptasarma
Department of Immunopathology, Postgraduate Institute of Medical Education and Research (PGIMER)
Tuesday, June 14, 2011 - 11:00 to 12:00
Aggregation and degradation are classically associated with protein storage. Though aggregation has been thought to be a possible consequence of protein degradation, it has never before been proposed to be a cause of degradation.. Using eight different proteins stored under physiological conditions at near-neutral pH, we have shown the development of a proteolytic/gelatinolytic activity in amyloid aggregate forms. The activity is associated with detergent-resistant high molecular weight (HMW) forms that can be electrophoresed on SDS-PAGE and examined zymographically. Evidence is seen for time-correlated, seeding-dependent gelatinolytic activity associated with HMW protein forms, which is diminished greatly by storage at low temperatures, extremes of pH, arginine, imidazole, BSA, azide, EDTA, DTT, PMSF (but not AEBSF), and diisopropyl fluorophosphate (DFP), suggesting involvement of surface serine residues in a novel aggregate-borne proteolytic activity. Naturally-formed aggregates (which progressively bleed away the conformational equilibrium) thus appear to use surface serines to perform metal-catalyzed, oxidative, peptide bond hydrolysis, indicating why proteins are invariably observed to be degraded during storage at near-neutral pH. The results also indicate a possible reason for the cytotoxicity of protein aggregates. The study suggests that a bi-directional cause-effect relationship operates between protein aggregation, and protein degradation, providing clues to the design of better conditions for long-term protein storage.