CD spectra were recorded using a JASCO 810 dichrograph flushed with N2 and equipped with a Peltier thermoregulation system. Spectra were recorded between 190 and 250 nm with scanning speed of 20 nm/min and data pitch of 0.2 nm. All measurements were carried out at 20°C on samples at 0.1 mg/ml in 10 mM phosphate buffer (pH 8) using a 1-mm-thick quartz cell. Each spectrum is the average of three acquisitions. The spectrum of buffer was subtracted from the protein spectrum. Spectra were smoothed using the “means-movement” smoothing procedure implemented in the Spectra Manager package. Mean molar residue ellipticity (MRE) values per residue were calculated as [θ] = 3300 m∆A/lcn, where l is the path length in centimeters, n is the number of residues, m is the molecular mass in daltons, and c is the concentration of the protein in milligrams per milliliter. CD spectra were also recorded in the presence of increasing GND concentrations. To this end, protein samples at 10 mg/ml were diluted to 0.1 mg/ml into 40 different GND solutions, ranging from 0 to 6 M, in 10 mM tris-HCl (pH 8). Chemical denaturation was monitored by measuring the ellipticity values at 222 nm. For each GND concentration, 20 measurements were performed and averaged. The denaturation midpoints were derived upon fitting the data to a sigmoid curve using the nonlinear least-squared R routine (Gauss-Newton).

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