title: Glutamine and Asparagine Side Chain Hyperconjugation-Induced Structurally Sensitive Vibrations.
abstract: We identified vibrational spectral marker bands that sensitively report on the side chain structures of glutamine (Gln) and asparagine (Asn). Density functional theory (DFT) calculations indicate that the Amide III(P) (AmIII(P)) vibrations of Gln and Asn depend cosinusoidally on their side chain OCCC dihedral angles (the χ3 and χ2 angles of Gln and Asn, respectively). We use UV resonance Raman (UVRR) and visible Raman spectroscopy to experimentally correlate the AmIII(P) Raman band frequency to the primary amide OCCC dihedral angle. The AmIII(P) structural sensitivity derives from the Gln (Asn) Cβ-Cγ (Cα-Cβ) stretching component of the vibration. The Cβ-Cγ (Cα-Cβ) bond length inversely correlates with the AmIII(P) band frequency. As the Cβ-Cγ (Cα-Cβ) bond length decreases, its stretching force constant increases, which results in an upshift in the AmIII(P) frequency. The Cβ-Cγ (Cα-Cβ) bond length dependence on the χ3 (χ2) dihedral angle results from hyperconjugation between the Cδ═Oϵ (Cγ═Oδ) π* and Cβ-Cγ (Cα-Cβ) σ orbitals. Using a Protein Data Bank library, we show that the χ3 and χ2 dihedral angles of Gln and Asn depend on the peptide backbone Ramachandran angles. We demonstrate that the inhomogeneously broadened AmIII(P) band line shapes can be used to calculate the χ3 and χ2 angle distributions of peptides. The spectral correlations determined in this study enable important new insights into protein structure in solution, and in Gln- and Asn-rich amyloid-like fibrils and prions.
authors.affiliation: Department of Chemistry, University of Pittsburgh , 219 Parkman Avenue, Chevron Science Center, Pittsburgh, Pennsylvania 15260, United States.
authors.forename: David
authors.initials: D
authors.lastname: Punihaole
authors.affiliation: Department of Chemistry, University of Pittsburgh , 219 Parkman Avenue, Chevron Science Center, Pittsburgh, Pennsylvania 15260, United States.
authors.forename: Zhenmin
authors.initials: Z
authors.lastname: Hong
authors.affiliation: Department of Chemistry, University of Pittsburgh , 219 Parkman Avenue, Chevron Science Center, Pittsburgh, Pennsylvania 15260, United States.
authors.forename: Ryan S
authors.initials: RS
authors.lastname: Jakubek
authors.affiliation: Department of Chemistry, University of Pittsburgh , 219 Parkman Avenue, Chevron Science Center, Pittsburgh, Pennsylvania 15260, United States.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Dahlburg
authors.affiliation: Department of Chemistry, University of Pittsburgh , 219 Parkman Avenue, Chevron Science Center, Pittsburgh, Pennsylvania 15260, United States.
authors.forename: Steven
authors.initials: S
authors.lastname: Geib
authors.affiliation: Department of Chemistry, University of Pittsburgh , 219 Parkman Avenue, Chevron Science Center, Pittsburgh, Pennsylvania 15260, United States.
authors.forename: Sanford A
authors.initials: SA
authors.lastname: Asher
mesh_terms: D001216:Asparagine / Q000737:chemistry*; D017666:Deuterium Oxide / Q000737:chemistry; D005973:Glutamine / Q000737:chemistry*; D015394:Molecular Structure; D013059:Spectrum Analysis, Raman / Q000379:methods; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D005973:Glutamine; D001216:Asparagine; D017666:Deuterium Oxide