UV–vis absorption spectrophotometry was performed using a Jasco V-650 spectrophotometer and 1 cm path length quartz cells. Lyophilized peptide was dissolved in 100 μL of phosphate buffered saline pH 7.4 (PBS; Thermo Fischer), and the concentration of each peptide was determined by measuring the absorbance at 205 nm and using a calculated extinction coefficient for each peptide due to the lack of aromatic residues in the peptides.55 (link),56 (link) For fluorescein-labeled peptides, the lyophilized solid was dissolved in 20 μL of dimethyl sulfoxide (Sigma) and then diluted to 100 μL with PBS. Peptide concentration was determined by measuring the absorbance at 495 nm.
Circular dichroism (CD) experiments were performed using a Jasco J-1500 circular dichroism spectrometer and 1 mm quartz cuvettes. 100 μM samples were prepared for each peptide in sodium phosphate buffer pH 7, and ellipticity was measured from 190 to 260 nm at 5 °C and 95 °C, respectively.
Fourier transform infrared (FT-IR) measurements were collected using a Jasco FT/IR-6800 FT-IR spectrometer. Peptide samples were solvent swapped into deuterated water and deuterated hydrochloric acid. 5 μL droplets of peptide samples were measured at RT, and the absorbance was recorded from 1200–1700 cm−1.
Circular dichroism (CD) experiments were performed using a Jasco J-1500 circular dichroism spectrometer and 1 mm quartz cuvettes. 100 μM samples were prepared for each peptide in sodium phosphate buffer pH 7, and ellipticity was measured from 190 to 260 nm at 5 °C and 95 °C, respectively.
Fourier transform infrared (FT-IR) measurements were collected using a Jasco FT/IR-6800 FT-IR spectrometer. Peptide samples were solvent swapped into deuterated water and deuterated hydrochloric acid. 5 μL droplets of peptide samples were measured at RT, and the absorbance was recorded from 1200–1700 cm−1.