Role of tertiary structures on the Root effect in fish hemoglobins(905 views) Ronda L, Merlino A, Bettati S, Verde C, Balsamo A, Mazzarella L, Mozzarelli A, Vergara A
Keywords: Hemoglobin, Microspectrophotometry, Oxygen Binding, Root Effect, X-Ray Crystallography, Deoxyhemoglobin, Proton, Allosterism, Article, Binding Affinity, Circular Dichroism, Conformational Transition, Crystal Structure, Ion Exchange Chromatography, Nonhuman, Priority Journal, Protein Tertiary Structure, X Ray Crystallography, Animal, Antarctica, Binding Site, Chemical Structure, Chemistry, Metabolism, Mammalia, Trematomus Bernacchii, Allosteric Regulation, Antarctic Regions, Fishes, Hydrogen-Ion Concentration, Models, Molecular, Protein Structure,
Affiliations: *** IBB - CNR ***
Department of Pharmacy, University of Parma, Parco Area delle Scienze 23/A, 43124 Parma, Italy
Department of Chemical Sciences, University of Naples Federico II, Via Cintia, I-80126, Naples, Italy
Institute of Biostructures and Bioimages, CNR, Naples, Via Mezzocannone 16, 80124, Naples, Italy
Department of Neurosciences, University of Parma, Parco Area delle Scienze 23/A, 43124 Parma, Italy
National Institute of Biostructures and Biosystems, Viale Medaglie d'Oro, 305, 00136 Rome, Italy
Institute of Protein Biochemistry, CNR, Via Pietro Castellino, 111, I-80131 Naples, Italy
References: Not available.
Role of tertiary structures on the Root effect in fish hemoglobins
Many fish hemoglobins exhibit a marked dependence of oxygen affinity and cooperativity on proton concentration, called Root effect. Both tertiary and quaternary effects have been evoked to explain the allosteric regulation brought about by protons in fish hemoglobins. However, no general rules have emerged so far. We carried out a complementary crystallographic and microspectroscopic characterization of ligand binding to crystals of deoxy-hemoglobin from the Antarctic fish Trematomus bernacchii (HbTb) at pH 6.2 and pH 8.4. At low pH ligation has negligible structural effects, correlating with low affinity and absence of cooperativity in oxygen binding. At high pH, ligation causes significant changes at the tertiary structural level, while preserving structural markers of the T state. These changes mainly consist in a marked displacement of the position of the switch region CD corner towards an R-like position. The functional data on T-state crystals validate the relevance of the crystallographic observations, revealing that, differently from mammalian Hbs, in HbTb a significant degree of cooperativity in oxygen binding is due to tertiary conformational changes, in the absence of the T-R quaternary transition. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins. (c) 2013 Elsevier B.V. All rights reserved.
Role of tertiary structures on the Root effect in fish hemoglobins