Figure 1.

TFE-induced secondary structural transitions for EGFP. (A and B) Far-UV CD spectra for 0.3 μM EGFP in 0–60% TFE at 37°C. (Insets) Selected spectra from the main plots, and the inset x axes' ranges are the same as the main plot ranges. (A) Data for EGFP at pH 2.4. The TFE concentrations for spectra with increasing negative ellipticity at 222 nm are 0, 2, 3, 4, 5, 7, 8, 10, 11, 12, 14, 15, 16, 17, 20, 22, 25, 30, 35, 40, 45, 60, and 50% TFE. (Insets) Spectra that share isodichroics. (Left y-axis range) −18–5 × 10³ deg cm² dmol⁻¹. (Right y-axis range) −37–65 × 10³ deg cm² dmol⁻¹. (B) Data for EGFP at pH 7.5. The TFE concentrations for spectra with increasing negative ellipticity at 222 nm are 0, 5, 10, 15, 17, 30, 32, 35, 40, 45, 50, and 60% TFE. (Left inset) Low-TFE spectra that are nearly invariant. (Right inset) High-TFE spectra that share an isodichroic point. (Left y-axis range) −9–18 × 10³ deg cm² dmol⁻¹. (Right y-axis range) −26–26 × 10³ deg cm² dmol⁻¹. (C) The mean residue ellipticity at 222 nm versus [TFE] for the spectra in A and B. (Error bars) Experimental uncertainties. (D) The CD spectra of EGFP in 60% TFE at various pH. The solution conditions for spectra with increasing negative ellipticity at 222 nm are 10 mM sodium phosphate (pH 7.5), 2 mM NaOH (pH 11.3), 10 mM borax (pH 9.3), 10 mM citrate-phosphate buffer (pH 4.6), 10 mM citrate-phosphate buffer (pH 3.5), 0.25 N sulfuric acid (pH 0.6), and 10 mM phosphoric acid (pH 2.4). (Inset) Ellipticity at 222 nm (in the same units as the main plot) as a function of pH for these samples. (Error bars) Experimental uncertainties.