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Keywords:

  • SR-CD;
  • synchrotron radiation circular dichroism;
  • VUV;
  • metmyoglobin;
  • carboprotein;
  • carbopeptide;
  • 2,2,2-TFE;
  • TFE;
  • α-helix;
  • protein folding

Abstract

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-α-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 α-helical tertiary structure, namely the globin fold and the 4-α-helix bundle motif. No significant differences were found between the CD spectra of the α-helical samples (metmyoglobin and carboprotein) in D2O solution. The use of 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. © 2005 Wiley Periodicals, Inc. Biopolymers 78: 46–52, 2005