Autocatalytic processes in cooperative mechanisms of prion diseases.
According to the leading theory, the agent responsible for prion diseases would be the conformational isomer PrP(Sc) of a cellular protein PrP(C), the pathogenic form PrP(Sc) multiplying by converting the normal protein into a likeness of itself. The pathogenic isoform could catalyze the conformational transition so that the process, taken as a whole, is autocatalytic. However, in this simple but atypic model, unrealistic values of rate parameters are needed in order to account for the kinetics of the propagation of prion diseases. In this paper, I show that these limits can be overcome by assuming that catalysis proceeds through a multimeric assembly of the pathogenic isoform of the prion protein. Such a structure would indeed be able to provide cooperativity both at the assembly and conformational change levels, strongly reinforcing the autocatalytic character of the activated process. Moreover, such a property is a prerequisite to endow the metabolic system with dynamic bistability. Together with a good agreement regarding experimental data, this analysis is closely akin to Griffith's original idea concerning the thermodynamic conditions required for autocatalyzed modifications of any protein.
Laurent
M
M
Service d'Imagerie Cellulaire, URA 1116 CNRS, Université Paris-Sud, Centre d'Orsay, France.
D000494:Allosteric Regulation; D000818:Animals; D002384:Catalysis; D008956:Models, Chemical; D018621:PrPC Proteins / Q000378:metabolism*; D018620:PrPSc Proteins / Q000378:metabolism*; D017096:Prion Diseases / Q000209:etiology / Q000378:metabolism*; D017510:Protein Folding; D013816:Thermodynamics
D018621:PrPC Proteins; D018620:PrPSc Proteins