A Fourier-transform infrared spectroscopic investigation of the hydrogen-deuterium exchange and secondary structure of the 28-kDa channel-forming integral membrane protein (CHIP28).

Fourier-transform infrared spectroscopy (FTIR) has been employed to investigate the structural properties of the 28-kDa channel-forming integral membrane protein (CHIP28) present in phospholipid vesicles suspended in aqueous media. This study reports the FTIR spectra of this membrane protein present in H2O and 2H2O. The secondary structure of the protein was determined and found to consist of 36% alpha-helical and 42% beta-sheet structures. These results are in close agreement with the results of a previous CD study [Van Hoek, A. N., Wiener, M., Bicknese, S., Miercke, L., Biwersi, J. & Verkman, A. S. (1993) Biochemistry 32, 11,847-11,856]. However, the results differ from those given in an FTIR analysis by the same workers who recorded FTIR spectra of the CHIP28 protein in a dehydrated state. An unusually high extent of hydrogen-deuterium exchange of the peptide groups of this protein occurs. The magnitude of the spectral changes observed upon exposure of the protein to 2H2O is greater than has been observed with any other membrane protein previously studied. Thus, over 80% of the peptide groups exchange within 5 min and the amide I band maximum shifts to low frequency by approximately 20 cm-1. This high hydrogen-deuterium exchange observed with the CHIP28 protein is consistent with the presence of an aqueous pore within the protein structure.