Figure 2.

Thermal denaturation of H6UctB (filled circles) and H6YfdW (open circles) monitored by CD as a function of pH. T_m values were determined using changes in molar ellipticity at 222 nm, corresponding to loss of helical structure. The lines connect average T_m values at each pH for H6UctB (solid line) and H6YfdW (dotted lines); H6UctB duplicates at pH 4.5 and 7.0 have completely overlapping symbols. The arrow at pH 4.0 for H6YfdW indicates a maximum for a partially observed melting transition. At pH 3.5, H6YfdW melted completely during equilibration at 20°C. Full CD spectra (recorded at 20°C) and thermal unfolding profiles are given as Figures S4–7 of the Supporting Information.