Conformational changes and development of proteinase K resistance in surface-immobilized PrP

The prion protein, and an increasing number of other cellular proteins, can undergo conformational transitions leading to soluble oligomers and insoluble aggregates. We have previously shown that the transition of the prion protein from its native form to its infectious (PrPSc) conformation can be monitored with epitope specific antibodies while the protein is immobilized on the surface of a Biacore surface plasmon resonance sensor chip. (Leclerc et al EMBO J 20:1547-1554 2001). The folding pathways leading to insoluble aggregates (amyloids) and soluble oligomers are believed to be distinct. We report here the use of epitope-specific antibody Fab fragments and surface plasmon resonance measurements on immobilized PrP to investigate the conditions leading to either folding pathway. We found that full-length SHaPrP(29-231) and truncated SHaPrP(90-231) prion protein can be induced to undergo the transition to proteinase K-resistant PrPSc aggregates on a sensor chip. This transition is temperature and buffer dependent and can be blocked by the presence of antibody Fab fragments binding to epitopes important for the conformational change. We demonstrate that the use of monoclonal antibodies combined with surface plasmon resonance technology is suitable to monitor the environmental conditions leading to conformational changes in the prion protein. The methodology is applicable to other amyloid- and oligomer-forming proteins and should be useful for the evaluation of antibodies or small molecules preventing protein misfolding.