Dynamic properties of some β-chain mutant hemoglobins (original) (raw)
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Evidence for Heme–Heme Excitonic Coupling in the Soret Circular Dichroism of Hemoglobin
Biochemical and Biophysical Research Communications, 1997
despite the absence of aromatic amino acid residues in In order to study interdimer heme-heme electronic the undecapeptide (2). The origin of induced CD in the interactions in human hemoglobin, the Soret circular case of the undecapeptide was recently explained by dichroism spectrum of the carboxy adduct is measured Blauer et al. (3), who concluded that coupled oscillator as a function of protein concentration, the spectrum interactions with peptide pp* transitions and high-enat the highest concentration representing primarily ergy peptide and thioether sulfur transitions, as well that of a 2 b 2 tetramers (93%) and the lowest concentraas inherent heme chirality arising from nonplanar distion representing primarily ab dimers (68%). The tettortions, are the dominant mechanisms contributing to ramer-dimer difference spectrum, obtained using sinthe Soret CD.
Conformational Dynamics of Heme Pocket in Myoglobin and Hemoglobin
Bulletin of the Korean Chemical Society, 2005
The conformational dynamics of heme pocket, a small vacant site near the binding site of heme proteinsmyoglobin (Mb) and hemoglobin (Hb), was investigated after photolysis of carbon monoxide from MbCO and HbCO in D2O solution at 283 K by probing time-resolved vibrational spectra of photolyzed CO. Two absorption bands, arising from CO in the heme pocket, evolve nonexponentially in time. The band at higher energy side blue shifts and broadens with time and the one at lower energy side narrows significantly with a negligible shift. These spectral evolutions are induced by protein conformational changes following photolysis that modify structure and electric field of heme pocket, and ligand dynamics in it. The conformational changes affecting the spectrum of photolyzed CO in heme pocket likely modulates ligand-binding activity.
Inorganic chemistry, 2016
We analyzed the oxygen (O2) and carbon monoxide (CO) binding properties, autoxidation reaction rate, and FeO2 and FeCO vibrational frequencies of the H64Q mutant of sperm whale myoglobin (Mb) reconstituted with chemically modified heme cofactors possessing a variety of heme Fe electron densities (ρFe), and the results were compared with those for the previously studied native [Shibata, T. et al. J. Am. Chem. Soc. 2010 , 132 , 6091 - 6098 ], and H64L [Nishimura, R. et al. Inorg. Chem. 2014 , 53 , 1091 - 1099 ], and L29F [Nishimura, R. et al. Inorg. Chem. 2014 , 53 , 9156 - 9165 ] mutants in order to elucidate the effect of changes in the heme electronic structure and distal polar interaction contributing to stabilization of the Fe-bound ligand on the functional and vibrational properties of the protein. The study revealed that, as in the cases of the previously studied native protein [Shibata, T. et al. Inorg. Chem. 2012 , 51 , 11955 - 11960 ], the O2 affinity and autoxidation reacti...
Biochemistry, 2008
Protein engineering strategies seek to develop a hemoglobin-based oxygen carrier with optimized functional properties, including (i) an appropriate O 2 affinity, (ii) high cooperativity, (iii) limited NO reactivity, and (iv) a diminished rate of autooxidation. The mutations αL29F, αL29W, αV96W and βN108K individually impart some of these traits and in combinations produce hemoglobin molecules with interesting ligand-binding and allosteric properties. Studies of the ligand-binding properties and solution structures of single and multiple mutants have been performed. The aromatic side-chains placed in the distal-heme pocket environment affect the intrinsic ligand-binding properties of the mutated subunit itself, beyond what can be explained by allostery, and these changes are accompanied by local structural perturbations. In contrast, hemoglobins with mutations in the α 1 β 1 and α 1 β 2 interfaces display functional properties of both "R"-and "T"-state tetramers because the equilibrium between them is altered. These mutations are accompanied by global structural perturbations, suggesting an indirect, allostery-driven cause for their effects. Combinations of the distalheme pocket and interfacial mutations exhibit additive effects in both structural and functional properties, contribute to our understanding of allostery, and advance protein-engineering methods for manipulating the O 2 binding properties of the hemoglobin molecule.
Protein dynamics. Comparative investigation on heme-proteins with different physiological roles
Biophysical Journal, 1991
We report the low temperature carbon monoxide recombination kinetics after photolysis and the temperature dependence of the visible absorption spectra of the isolated aSH_CO and 13SH-CO subunits from human hemoglobin A in ethylene glycol/water and in glycerol/water mixtures. Kinetic measurements on sperm whale (Physeter catodon) myoglobin and previously published optical spectroscopy data on the latter protein and on human hemoglobin A, in both solvents, (Cordone, L., A. Cupane, M. Leone, E. Vitrano, and D. Bulone. 1988. J. Mol. Biol. 199:312-218) are taken as reference.
Ligand binding to heme proteins: II. Transitions in the heme pocket of myoglobin
Biophysical Journal, 1993
Phenomena occurring in the heme pocket after photolysis of carbonmonoxymyoglobin (MbCO) below about 100 K are investigated using temperature-derivative spectroscopy of the infrared absorption bands of CO. MbCO exists in three conformations (A substates) that are distinguished by the stretch bands of the bound CO. We establish connections among the A substates and the substates of the photoproduct (B substates) using Fourier-transform infrared spectroscopy together with kinetic experiments on MbCO solution samples at different pH and on orthorhombic crystals. There is no one-to-one mapping between the A and B substates; in some cases, more than one B substate corresponds to a particular A substate. Rebinding is not simply a reversal of dissociation; transitions between B substates occur before rebinding. We measure the nonequilibrium populations of the B substates after photolysis below 25 K and determine the kinetics of B substate transitions leading to equilibrium. Transitions between B substates occur even at 4 K, whereas those between A substates have only been observed above about 160 K. The transitions between the B substates are nonexponential in time, providing evidence for a distribution of substates. The temperature dependence of the B substate transitions implies that they occur mainly by quantum-mechanical tunneling below 10 K. Taken together, the observations suggest that the transitions between the B substates within the same A substate reflect motions of the CO in the heme pocket and not conformational changes. Geminate rebinding of CO to Mb, monitored in the Soret band, depends on pH. Observation of geminate rebinding to the A substates in the infrared indicates that the pH dependence results from a population shift among the substates and not from a change of the rebinding to an individual A substate. INTRODUCTION1 Myoglobin is a globular protein consisting of 153 amino acids and a heme (Fe-protoporphyrin IX) as the prosthetic group. Textbooks state that the function of Mb is the reversible binding of small ligands such as dioxygen (02) and carbon monoxide (CO) at the heme iron (Stryer, 1988). One could expect such a binding process to be simple. It was indeed originally described as a one-step process (Antonini and Brunori, 1971). Flash photolysis experiments performed over wide ranges in time and temperature imply, however, that the binding process is far from simple (Austin et al., 1975). Four phenomena, in particular, produce complexity: 1. multiple wells along the reaction coordinate, 2. confor-mational substates, 3. protein relaxation after photodissociation, and 4. thermal fluctuations. In the following, we briefly describe how these phenomena affect the ligand binding to myoglobin. Multiple wells along the reaction coordinate In the simplest model, CO in the solvent binds to the heme iron in one step. Flash photolysis data, however, show evidence for multiple processes. A model that describes the salient features of the kinetic data uses three wells (states) along the reaction coordinate, A i± B S.