title: Occurrence of bifurcated three-center hydrogen bonds in proteins.
abstract: Analysis of 13 high-resolution protein X-ray crystal structures shows that 1204 (24%) of all the 4974 hydrogen bonds are of the bifurcated three-center type with the donor X-H opposing two acceptors A1, A2. They occur systematically in alpha-helices where 90% of the hydrogen bonds are of this type; the major component is (n + 4)N-H ... O = C(n) as expected for a 3.6(13) alpha-helix, and the minor component is (n + 4)N-H ... O = C(n + 1), as observed in 3(10) helices; distortions at the C-termini of alpha-helices are stabilized by three-center bonds. In beta-sheets 40% of the hydrogen bonds are three-centered. The frequent occurrence of three-center hydrogen bonds suggests that they should not be neglected in protein structural studies.
authors.affiliation: Institut für Kristallographie, Freie Universität Berlin, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Preissner
authors.forename: U
authors.initials: U
authors.lastname: Egner
authors.forename: W
authors.initials: W
authors.lastname: Saenger
mesh_terms: D006860:Hydrogen Bonding; D008433:Mathematics; D008958:Models, Molecular; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D011506:Proteins