Figure 3. CD-monitored trifluoroethanol-titration curves of α₂-peptide variants of 18.5-kDa MBP.

Data are presented for four α₂-peptides (S72–S107) of myelin basic protein (MBP): unmodified, singly- (PhT92, PhT95) and doubly- (PhT92–PhT95) phosphorylated. The peptides were titrated with TFE, and monitored by CD spectroscopy at 222 nm in order to assess the differences in their ability to form α-helical structure. All samples contained 20 mM HEPES-NaOH, pH 7.4, and data were collected at 25°C. The solid circular points are representative data of a forward-titration experiment, whereas the open circular points are from the corresponding reverse-titration experiments. The reverse-titration data were offset to match pre- and post-transition baselines to facilitate comparison. Forward- and reverse-titration data are highly coincident which is indicative of an equilibrium folding transition amenable to thermodynamic analysis. The red lines are fits of the forward-titration data to a 2-state (disorder↔α-helix) equilibrium model [69] to obtain the midpoint ([TFE]_mid) of the curves, as well as the ΔG^H2O of the transition (Table 3).