Comparing the Folding and Misfolding Energy Landscapes of Phosphoglycerate Kinase

Abstract

Understanding the sequence specific partitioning of polypeptides between protein folding and amyloid formation is of outstanding physiological and pathological importance. Using yeast phosphoglycerate kinase as model, here we identify the features of the energy landscape that decide the fate of the protein: folding or amyloidogenesis. Structure formation was initiated from the acid-unfolded state by stopped-flow or manual mixing, and monitored by tryptophan and thioflavin T fluorescence from 1 ms to 10 days. Solvent conditions were gradually shifted between folding and amyloidogenesis and the properties of the energy landscape governing structure formation were reconstructed. A continuous transition of the energy landscape between folding and amyloid formation was observed. In the early steps of both folding and misfolding, the protein searches through a hierarchically structured energy landscape to form a molten globule on the seconds timescale. From this intermediate structure, folding to the native structure happens in a cross-barrier step in a few minutes, while amyloidogenesis progresses much slower, on the days and weeks timescale. As conditions are changed from folding to misfolding, formation of the native structure slows down indicating the increase of the barrier separating the molten globule and native states. In the meantime, the native state becomes more unstable as well. Amyloid formation is only observed among solvent conditions where folding is absent.