title: Strength of a bifurcated H bond.
abstract: Macromolecules are characterized by their particular arrangement of H bonds. Many of these interactions involve a single donor and acceptor pair, such as the regular H-bonding pattern between carbonyl oxygens and amide H(+)s four residues apart in α-helices. The H-bonding potential of some acceptors, however, leads to the phenomenon of overcoordination between two donors and one acceptor. Herein, using isotope-edited Fourier transform infrared measurements and density functional theory (DFT) calculations, we measured the strength of such bifurcated H bonds in a transmembrane α-helix. Frequency shifts of the (13)C=(18)O amide I mode were used as a reporter of the strength of the bifurcated H bond from a thiol and hydroxyl H(+) at residue i + 4. DFT calculations yielded very similar frequency shifts and an energy of -2.6 and -3.4 kcal/mol for the thiol and hydroxyl bifurcated H bonds, respectively. The strength of the intrahelical bifurcated H bond is consistent with its prevalence in hydrophobic environments and is shown to significantly impact side-chain rotamer distribution.
authors.affiliation: Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmund J. Safra Campus, Jerusalem 91904, Israel.
authors.forename: Esther S
authors.initials: ES
authors.lastname: Feldblum
authors.forename: Isaiah T
authors.initials: IT
authors.lastname: Arkin
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002247:Carbon Isotopes / Q000737:chemistry; D006860:Hydrogen Bonding; D046911:Macromolecular Substances / Q000737:chemistry*; D008956:Models, Chemical; D010103:Oxygen Isotopes / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D046911:Macromolecular Substances; D010103:Oxygen Isotopes
keywords: FTIR; membrane proteins; protein structure