Synchrotron radiation circular dichroism spectroscopy applied to metmyoglobin and a 4-α-helix bundle carboprotein

The novel technique, synchrotron radiation-based circular dichroism (SR-CD). has been applied to the study of metmyoglobin and a carboprotein (carbohydrate-based peptide with protein tertiary structure) with 4-alpha-helix bundle structure, as well as a carbopeptide (carbohydrate-based peptide) with a truncated peptide sequence. The use of synchroton radiation (SR) enabled circular dichroism (CD) measurements in the vacuum ultraviolet (VUV) down to 168 nm in D2O and 160 nm in 2,2,2-trifluoroethanol (TFE). The band shape in the CD spectra in the low wavelength region was studied, comparing samples with two types of alpha-helical tertiary structure, namely the globin fold and the 4-alpha-helix bundle motif. No significant differences were found between the CD spectra of the a-helical samples (metinvoglobin and carboprotein) in D,O solution. The use qf 2,2,2-TFE (TFE) as solvent clearly alters the VUV CD but the two samples have very similar CD spectra. The solvent-induced denaturing of metmyoglobin in TFE was observed using absorption and CD spectroscopy of the Soret band, with results indicating heme release. The VUV spectrum Of TFE-denatured metmyoglobin exhibits dramatic differences in comparison with previous studies of the native enzyme in aqueous solution. The implications of this observation are discussed. (c) 2005 Wiley Periodicals, Inc.