A Native-Like Conformation for the C-Terminal Domain of the Prion Ure2p within its Fibrillar Form

摘要

The tertiary and quaternary structures of infectious proteins, termed prions, are of particular interest because according to the "protein-only" hypothesis, they hold the information responsible for prion trait self-propagation. The nature of the structural changes at the origin of a class of neurological prion disorders in mammals and several prion phenotypes in yeast and fungi' remains mysterious in the absence of information at atomic resolution. Such information can be provided by solid-state NMR spectroscopy, as it has recently been shown that full-length fibrils lead to well-resolved spectra, which contain detailed structural information. Yeast prions are a convenient tool to study the molecular arrangement of prion proteins as they are innocuous. Herein, we present for the Ure2 prion (Ure2p) the measurement of structural probes specific for over 175 residues spread throughout the Ure2p C-terminal domain, and we show that the globular domain of the yeast prion Ure2p is largely identical in isolation (in crystalline form) and in the context of the full-length prion fibrils, obtained in vitro under physiological conditions. Interestingly, we find that the Ure2p globular domain, as seen on the NMR time scale of milliseconds and longer, adopts in full-length Ure2p fibrils a single conformation, as opposed to the conformation within crystals. This is astonishing when considering that, when proteins assemble into crystals, the conformational variability (sometimes termed the structural flexibility) of the polypeptide chain is often reduced. In contrast, for fibrils, a form of conformational variability called polymorphism is often found upon fibrilization.