Sds micelles

Circular dichroism spectra of the peptides in different environments were obtained at 25°C by using a J-820 spectropolarimeter (Jasco, Tokyo, Japan). The peptide samples were recorded at a final concentration of 150 µM in 10 mM sodium phosphate buffer, pH 7.4 (mimicking the aqueous environment), 30 mM SDS micelles (mimicking the negatively charged prokaryotic membrane comparable environment, Sigma), and 50% TFE (mimicking the hydrophobic environment of the microbial membrane, Sigma). The samples were loaded in a rectangular quartz cell (0.1 cm path length), and the spectra were recorded at a scanning speed of 10 nm/min in the wavelength range of 190 to 250 nm.

The secondary structures of the peptides in different environments were measured using a J-820 spectropolarimeter (Jasco, Tokyo, Japan). The spectra were recorded at a scanning speed of 10 nm/min at wavelengths ranging from 195 to 250 nm in sodium phosphate buffer (10 mM, pH 7.4), SDS micelles (30 mM, Sigma), or TFE (50%, Sigma). An average of three scans was collected for each peptide. The final concentration of the peptides was 150 μM.
The acquired CD signal spectra were converted to the mean residue ellipticity using the following equation:

where θ_M is the mean residue ellipticity [deg.cm².dmol⁻¹], θ_obs is the observed ellipticity corrected for the buffer at a given wavelength [mdeg], c is the peptide concentration [mM], l is the path length [mm], and n is the number of amino acids.

The solutions were prepared at a 150 µM peptide concentration in 10 mM PBS (pH 7.4, to mimic an aqueous environment), 50% TFE (to mimicthe hydrophobic environment of the microbial membrane) (Sigma), and 30 mM SDS micelles (negatively charged prokaryotic membrane comparable environment) (Sigma). The CD spectra were measured with a CD spectropolarimeter (Jasco, J-820, Tokyo, Japan) at 25°C, using a 0.1 cm path length rectangular quartz cell. The spectra were recorded at between 190 and 250 nm at 10 nm/min scanning speed. At least three scans were conducted for each peptide sample.
The acquired CD spectra were converted to the mean residue ellipticity through the following equation:
where θM is the mean residue ellipticity [deg.cm2.dmol-1], θobs is the observed ellipticity corrected for the buffer at a given wavelength [mdeg], c is the peptide concentration [mM], l is the path length [mm], and n is the number of amino acids.
The percentage of α-helical structure was calculated as followings:
where [θ]₂₂₂ is the experimentally observed mean residue ellipticity at 222 nm, and values for [θ]⁰ and [θ]¹⁰⁰ which correspond to 0 and 100% a-helix content at 222 nm, are estimated to be −2000 and −32000, respectively [28] (link), [29] (link).