Structure of a Transient Intermediate at the Edge between Folding and Aggregation into Amyloid Fibrils from NMR Relaxation Dispersion Experiments

摘要

Protein folding intermediates are implicated in amyloid fibril formation but difficult to characterize. CPMG NMR relaxation dispersion experiments allowed us to detect a previously unknown intermediate on the folding pathway of the Fyn SH3 A39V/N53P/V55L and to reconstruct chemical shifts and RDCs/RCSAs for this 2% populated intermediate. Calculation of the high-resolution structure of the “invisible” intermediate from these experimental restraints using the Camshift strategy revealed a native-like arrangement of 4 of the 5 native beta-strands stabilized by several non-native long-range interactions. By contrast, the C-terminus remains disordered, leaving an aggregation-prone strand exposed. Accordingly, mutants mimicking this intermediate spontaneously form amyloid fibrils. This structure provides a detailed picture of how an intermediate can facilitate both, folding but also misfolding/aggregation.