FT-IR spectroscopy of the major coat protein of M13 and Pf1 in the phage and reconstituted into phospholipid systems

FT-IR spectroscopy has been applied to study the secondary structure of the major coat protein of Pf1 and M13 as present in the phage and reconstituted in DOPG and mixed DOPC/DOPG (4/1) bilayers. Infrared absorbance spectra of the samples were examined in dehydrated films and in suspensions of D2O and H2O. The secondary structure of the coat protein is investigated by second-derivative analysis, Fourier self-deconvolution, and curve fitting of the infrared bands in the amide I region (1600-1700 cm-1). It is found that, in dehydrated films of Pf1 and M13 phage, the amide I region contains three bands located at about 1633, 1657, and 1683 cm-1, that are assigned to hydrogen-bonded turn, alpha-helix/random coil, and non-hydrogen-bonded turn, respectively. From a comparison of the infrared spectra in dehydrated film with those in aqueous suspension, the percentages of secondary structure were found with an accuracy of about +/- 5%. For the coat protein of Pf1 phage, the FT-IR quantification gives 69% alpha-helix conformation, 19% turn structure, and 12% random coil structure. For Pf1 coat protein in the membrane-embedded state, the amount of alpha-helix is 57%, whereas 42% is in a turn structure and 1% in a random coil structure. The same assignment strategy was used for the analysis of the data obtained for M13 coat protein reconstitution into phospholipid systems. For M13 coat protein in the phage, this gives 75% alpha-helix conformation, 21% turn structure, and 4% random coil structure.(ABSTRACT TRUNCATED AT 250 WORDS)