Infrared amide I' band of the coiled coil

The Fourier transform infrared (FTIR) spectra of several coiled-coil proteins have been shown to possess unusual features in the amide I' region. Band maxima occur in the vicinity of 1630 cm(-1), with component bands at higher frequency. This is well below the observed band at 1650 cm(-1) found in standard alpha-helical polypeptides such as poly-L-alanine. Normal mode calculations on models of the coiled-coil structure have been performed to investigate this issue. We find that the observed band profile can be reproduced with very small random variations on the phi,psi of tropomyosin. We believe that the shift to lower frequency is due to additional hydrogen bonding of the solvent accessible backbone CO groups to water.