Figure 2. DMPC state-dependence of KV1 conformation.

A. Deconvolved spectra of KV1 polypeptide (10 mg/ml) in 100 mg/ml DMPC with 10% TFE (dotted line) or 30% TFE (solid line) at 30°C. Peptide was prepared as a thin film, and then taken up into DMPC in TFE, before addition of deuterated PBS to give the appropriate final concentrations of TFE and DMPC. B. Deconvolved spectra of KV1 polypeptide (10 mg/ml) in 30% TFE with 50 mg/ml DMPC (dotted line) or 100 mg/ml DMPC (solid line) at 30°C. Peptide was prepared as in Panel a. C. Deconvolved spectra of KV1 polypeptide (10 mg/ml) in 40% TFE with 25 mg/ml DMPC (dotted line) or 100 mg/ml DMPC (solid line) at 30°C. Peptide was prepared as in Panel a. D. Amide I regions of deconvolved spectra of KV1 polypeptide (10 mg/ml) reconstituted by thin-film method into DMPC vesicles (100 mg/ml) in deuterated PBS with 40% v/v TFE at a range of temperatures during cooling from 20°C to 5°C (blue lines) and heating from 5°C to 30°C (red lines). The initial 1651 cm⁻¹ absorbance peak is indicated; shifts in this initial peak are highlighted with arrows. E. Comparison of absorbance of infrared light at 1647 cm⁻¹ relative to absorbance at 1652 cm⁻¹, calculated from deconvoluted spectra, of KV1 polypeptide reconstituted by the thin-film method into DMPC vesicles (as in Panel a) at a range of temperatures during cooling from 20°C to 5°C (solid lines) and heating from 5°C to 30°C (dashed lines). DMPC phase transition points T₂ and T₃ are denoted next to their respective temperatures. F. Amide I region of KV1 polypeptide, 5°C minus 30°C difference spectrum, experimental conditions as in Panel D.G. Lipid phase transition - effect of decreased lipid hydration on the absorbance frequency of the ester carbonyl stretching band. Comparison of normalized absorbance of infrared light by DMPC at 1729 cm⁻¹(open squares) and at 1730 cm⁻¹ (filled squares), calculated from deconvolved spectra of DMPC (with KV1 polypeptide reconstituted by the thin-film method as in Panel b) at a range of temperatures during cooling from 20°C to 5°C and heating from 5°C to 30°C.H. Lipid phase transition - effect of gel-fluid transition on the absorbance frequency of the CH₂ symmetrical stretching band. Absorbance frequency of the ∼2850 cm⁻¹-centred lipid hydrocarbon chain CH₂ symmetrical streching band was monitored with increasing temperature, from the absorbance spectra of DMPC (with KV1 polypeptide reconstituted by the thin-film method as in Panel b) at a range of temperatures during heating from 5°C to 80°C. The points were fitted with a standard Boltzmann function, giving values for A1 and A2 of 2854.8 cm⁻¹ and 2856.0 cm⁻¹ respectively, and a midpoint of 25.0±0.4°C for the DMPC gel-fluid transition (Chi² = 4.2×10⁴).