Effect of GdmCl on the fluorescence emission of SP-B_N.

<p>(A) Fluorescence intensity emission (FI) of the propeptide in 5 mM AMT buffer, 150 mM NaCl pH 7 with 0–6.6 M GdmCl after excitation at 290 nm <i>vs</i> the wavelength. Spectrum without GdmCl (control, solid line), with 2.3 M GdmCl (dashed line), 6 M GdmCl (dotted line) or 6 M GdmCl and ulterior dialysis towards the same buffer (renatured, solid line) were recorded at 25°C. Arbitrary units (a.u.) were employed. (B) Variation of the fluorescence emission at 350 nm with 0–6.6 M GdmCl. The line is a fit of data in the 1.5–6.6 M interval to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158430#pone.0158430.e001" target="_blank">Eq (1)</a> (r = 0.99). Inset: Comparison of secondary structure (% [θ]²²⁰, red circle, data and fitting from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158430#pone.0158430.g001" target="_blank">Fig 1B</a>) and tertiary structure (FI₃₅₀N·(FI₃₅₀)^-1·10²), blue symbol, data and fitting from Fig 3B, N is the native form). (C) Phase diagram of 0–6.6 M GdmCl based on the fluorescence emission of the propeptide at two wavelengths. Solid lines are the fit of experimental data by linear regression: 0–2.8 M (r = 0.96) and 3.5 to 6.6 M (r = 0.98). Dotted line (2.8–3.5 M) is not a fit. I₁ and I₂ are intermediate states in the protein GdmCl-induced unfolding; N and U as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158430#pone.0158430.g001" target="_blank">Fig 1</a>. Numbers beside the points are denaturant concentration.