Circular dichroism spectra of the wsMUR-TM_v2 compared with the originally designed wsMUR-TM at buffer condition of 5 mM sodium phosphate, pH = 7.0 at temperature of 25°C. The two proteins displayed similar spectra. Estimates of helical content obtained using the two spectra are presented in table 1. MRME = mean residue molar ellipticity; wsMUR-TM = first variant of the water-soluble human μ-opioid receptor transmembrane portion; wsMUR-TM_v2 = modified (second) variant of the water-soluble human μ-opioid receptor transmembrane portion.