Figure 3. PGR contains polyproline type II helix.

Panel (a) shows the CD spectra of PGR from 5° C in magenta to 95° C in red, collected in 10° C increments. These spectra resemble those from PPII-containing peptides, showing PPII transitioning to random coil at increasing temperatures. The mean residue ellipticity, [θ] (degrees cm² dmol⁻¹ residue⁻¹), in thousands is plotted against wavelength. The inset shows the temperature dependence of the minimum at 200 nm. In panel (b), a difference plot of the spectrum at each temperature subtracted from the 95° C spectrum is displayed. The inset shows the temperature dependence of the local maximum at 222 nm, associated with PPII content.