Protein-Folding Mechanisms Elucidated Using Chaotic-Flow SAXS
While there is emerging consensus in the protein folding community concerning the behavior of proteins under unfolding conditions, the occurrence of unfolded states under physiological (native) conditions and their propensity to aggregate are the basis of several human pathologies. Valuable insights into these transient species were obtained by taking advantage of the temporal resolution afforded by combining time-resolved fluorescence and continuous (in this case chaotic) flow SAXS (CF-SAXS) with all atom simulations and polymer theory. A group of researchers led by the Raleigh lab (Stony Brook University) used the 59 amino acid N-terminal domain of the ribosomal protein L9 (NTL9), which has a well-studied two state folding mechanism. By introducing FRET pairs several pairwise distance distributions were measured in the unfolded and native conditions in equilibrium and also the unfolded states in native conditions using a continuous flow mixer Interestingly chain contraction as indicated by fluorescence decay was observed well within the dead time of the mixer (~40 µs) showing that chain collapse happens considerably faster than the time-scale required for completion of the folding process (2.5 ms for NTL9 …