Circular dichroism (CD). Far-UV CD spectra were obtained using a Jasco J-810 spectropolarimeter (Jasco Inc., Easton, MD, USA) over the wavelength range from 195 to 250 nm, at 25˚C. Measurements were performed in a 1 cm quartz cuvette at a rate of 100 nm/min, bandwidth of 1 nm, response time of 2 s, **data** pitch of 1 nm, and accumulation of 10 as described [37]. CD **data** are shown as the mean residue ellipticity (deg cm 2 /dmol) obtained after subtracting the baseline, smoothing, and **data** normalization. CD spectra for OsttaDSP (0.1-0.5 mg/ml) were recorded in 20 mM K-phosphate buffer, pH 7.4.