title: Vacuum-Ultraviolet Circular Dichroism Spectra of Escherichia coli Dihydrofolate Reductase and Its Mutants: Contributions of Phenylalanine and Tyrosine Side Chains and Exciton Coupling of Two Tryptophan Side Chains.
abstract: Vacuum-ultraviolet (VUV) circular dichroism (CD) spectroscopy has recently been used for secondary structure analysis of proteins; however, the contribution of aromatic side chains to protein VUV CD spectra is unresolved. In this report, VUV CD spectra of 10 Escherichia coli dihydrofolate reductase (DHFR) mutants, in which each phenylalanine or tyrosine residue was mutated to leucine, were measured down to 175 nm at 25 °C and pH 8.0 to elucidate the contributions of these aromatic side chains to the high-energy transitions of peptide bonds. The VUV CD spectra of these mutants were different from the spectrum of the wild-type protein, indicating that the contribution of the phenylalanine and tyrosine side chains of DHFR extends to the VUV region. Furthermore, the VUV CD spectrum and the folate- or NADP(+)-induced spectral change of F103L mutant DHFR indicated a modification and regeneration of exciton coupling between the Trp47 and Trp74 side chains, respectively, suggesting that exciton coupling may also contribute to the CD spectrum of DHFR in the VUV region. These results should be useful for theoretically characterizing the contribution of aromatic side chains to protein CD spectra, leading to the improvement of protein secondary-structure analysis by VUV CD spectroscopy.
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University , Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Ohmae
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University , Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Suguru
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University , Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Yurina
authors.initials: Y
authors.lastname: Miyashita
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University , Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Katsuo
authors.initials: K
authors.lastname: Katayanagi
authors.affiliation: Hiroshima Synchrotron Radiation Center, Hiroshima University , 2-313 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Matsuo
mesh_terms: D002942:Circular Dichroism / Q000379:methods*; D004926:Escherichia coli / Q000201:enzymology*; D009154:Mutation; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D013762:Tetrahydrofolate Dehydrogenase / Q000737:chemistry* / Q000235:genetics; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D014364:Tryptophan; D013762:Tetrahydrofolate Dehydrogenase