title: The bis-histidyl complex in hemoproteins: A detailed conformational analysis of database protein structures and the case of Antarctic fish hemoglobins.
abstract: The properties of hemoproteins strictly depend on the type and orientation of axial ligands. Here, the orientations of axially coordinated His in bis-His complexes and the heme geometry in protein data bank have been analyzed. The effect of the bis-histidyl formation on the heme cavity of Antarctic fish hemoglobins has been also evaluated. The results show that protein matrix exerts a major effect on the conformation of axially ligated histidines: the imidazoles in bis-His complexes occupy a preferred relative orientation in globins and in model systems, whereas they adopt a variety of relative orientations in other hemoproteins. The bis-histidyl adducts affect the heme geometry inducing larger distortions from planarity with respect to other ligands. These deviations are larger in bis-His multiheme cytochromes than in globins. In Antarctic fish hemoglobins the bis-histidyl adduct adopts preferentially a distorted coordination and the formation of the bis-His complex induces a slight but significant modification in the shape, area and volume of the heme cavity.
authors.affiliation: Department of Chemistry, University of Naples "Federico II", Complesso Universitario di Monte S. Angelo, Via Cintia, I-80126 Naples, Italy; Institute of Biostructures and Bioimages, CNR, Via Mezzocannone 16, I-80134 Naples, Italy.
authors.forename: Antonello
authors.initials: A
authors.lastname: Merlino
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vergara
authors.forename: Filomena
authors.initials: F
authors.lastname: Sica
authors.forename: Lelio
authors.initials: L
authors.lastname: Mazzarella