Figure 4.

The early folding intermediate of mβ₂m. (A) The assignment walk on the Cα atoms of the real-time BEST-HNCA spectrum of mβ₂m collected 5 min after refolding was initiated by urea dilution at pH 6.2. (B) Predicted S² parameters for the folding intermediate of mβ₂m. The intense peaks shown in Figure 3E are shown in dark blue. The S² parameters of the native state are shown as light blue bars and as a red line. (C) Residues observed in the real-time spectrum of the folding intermediate are highlighted in red in the structure of mβ₂m. Pro 32 is shown as yellow spheres. (D) Far-UV CD spectra of native mβ₂m at pH 6.2 (green) and of the folding intermediate 3 min after folding was initiated by a pH jump from pH 2.0 to pH 6.2 (red). (E) Normalized fluorescence signal at the end of each stopped-flow transient (20 s) as a function of urea concentration for mβ₂m in the absence (red) or presence (black) of 0.4 M sodium sulfate. The data were fitted globally to a two-state model (see Methods).