The bis-histidyl complex in hemoproteins: A detailed conformational analysis ofdatabase protein structures and the case of Antarctic fish hemoglobins

摘要

The properties of hemoproteins strictly depend on the type and orientation of axial ligands. Here, theorientations of axially coordinated His in bis-His complexes and the heme geometry in protein data bank havebeen analyzed. The effect of the bis-histidyl formation on the heme cavity of Antarctic fish hemoglobins hasbeen also evaluated. The results show that protein matrix exerts a major effect on the conformation of axiallyligated histidines: the imidazoles in bis-His complexes occupy a preferred relative orientation in globins and inmodel systems, whereas they adopt a variety of relative orientations in other hemoproteins. The bis-histidyladducts 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 hemoglobinsthe bis-histidyl adduct adopts preferentially a distorted coordination and the formation of the bis-His complexinduces a slight but significant modification in the shape, area and volume of the heme cavity.