Allosteric Intermediates in Hemoglobin. 2. Kinetic Modeling of HbCO Photolysis<sup>,</sup>

Goldbeck, Robert A.; Paquette, S. J.; Björling, Sofie C.; Kliger, David S.

doi:10.1021/bi952248k

Cited by 44 publications

(82 citation statements)

References 42 publications

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“…Finally, the value 1.4 × 10 −3 obtained for the affinity ratio c is within the range of values previously obtained (i.e., 0.8-6.1 × 10 −3 ), and close to that obtained from the equilibrium CO binding data of Perrella et al (24,25). In a nutshell, present analysis confirms that in HbA the largest structural rearrangement associated to the R-T transition (i.e., the relative αβ dimers rotation and translation) is faster than what has been obtained by TR-OA data (2,3,23,26), though consistent with the faster step seen by UVRR and assigned to the relaxation of Trp37β (5, 10).…”

Section: Resultssupporting

confidence: 90%

“…2 with α ¼ − logðsÞ∕ logðcÞ; the values reported in Table 1 yield α ¼ 0.33 and 0.81 for HbA and HbYQ, respectively. In the case of HbA, the difference between our estimate and the value of α ¼ 0.17 determined by TR-OA data (23) may be traced to the proposed stepwise character of the R-T allosteric transition (10,14,26). Following this idea, Cammarata et al (13) proposed that TR-WAXS essentially monitors a first step of the R-T transition of HbA (namely the αβ dimers rotation and translation), while TR-OA monitors a second slower step associated with a more localized reorganization around the active site; accordingly, the transition states explored by TR-WAXS and TR-OA spectroscopy are not the same (Fig.…”

Section: Discussionmentioning

confidence: 58%

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The Monod-Wyman-Changeux allosteric model accounts for the quaternary transition dynamics in wild type and a recombinant mutant human hemoglobin

Levantino

Spilotros

Cammarata

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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The acknowledged success of the Monod-Wyman-Changeux (MWC) allosteric model stems from its efficacy in accounting for the functional behavior of many complex proteins starting with hemoglobin (the paradigmatic case) and extending to channels and receptors. The kinetic aspects of the allosteric model, however, have been often neglected, with the exception of hemoglobin and a few other proteins where conformational relaxations can be triggered by a short and intense laser pulse, and monitored by time-resolved optical spectroscopy. Only recently the application of time-resolved wide-angle X-ray scattering (TR-WAXS), a direct structurally sensitive technique, unveiled the time scale of hemoglobin quaternary structural transition. In order to test the generality of the MWC kinetic model, we carried out a TR-WAXS investigation in parallel on adult human hemoglobin and on a recombinant protein (HbYQ) carrying two mutations at the active site [Leu(B10)Tyr and His(E7) Gln]. HbYQ seemed an ideal test because, although exhibiting allosteric properties, its kinetic and structural properties are different from adult human hemoglobin. The structural dynamics of HbYQ unveiled by TR-WAXS can be quantitatively accounted for by the MWC kinetic model. Interestingly, the main structural change associated with the R-T allosteric transition (i.e., the relative rotation and translation of the dimers) is approximately 10-fold slower in HbYQ, and the drop in the allosteric transition rate with ligand saturation is steeper. Our results extend the general validity of the MWC kinetic model and reveal peculiar thermodynamic properties of HbYQ. A possible structural interpretation of the characteristic kinetic behavior of HbYQ is also discussed.time-resolved X-ray scattering | protein conformational changes | cooperativity | flash photolysis E ver since the publication of the Monod-Wyman-Changeux paper on allostery (1), hemoglobin (Hb) has been considered the prototype of an allosteric protein; the molecular basis of positive cooperativity in O 2 binding involving a ligand-linked shift between two different quaternary states. The dynamics of ligand rebinding and of the tertiary and quaternary allosteric changes of tetrameric human Hb have been investigated, by-and-large, using transient spectroscopy in the picosecond to millisecond time range, following laser-induced photolysis of the ligand-heme iron bond. Starting with the carbon monoxide adduct HbCO in the allosteric quaternary state called R 4 , complete photolysis yields the unliganded R 0 state; the destiny of this photoproduct is a complex time-dependent process involving competing events such as ligand rebinding and (tertiary and quaternary) conformational decays. Changes in the optical and resonance Raman spectra of the different states have provided, over the last four decades, a quantitative estimate of the rates of the competing events (2-5). For a review on time-resolved optical absorption (TR-OA) data describing conformational decays as well as rebinding in the dark of a ligand...

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Section: Resultssupporting

confidence: 90%

Section: Discussionmentioning

confidence: 58%

The Monod-Wyman-Changeux allosteric model accounts for the quaternary transition dynamics in wild type and a recombinant mutant human hemoglobin

Levantino

Spilotros

Cammarata

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…In the case of aqueous COMb, the relaxation is largely complete within tens of picoseconds but with some residual components persisting well beyond 10 ns (23,28,48,50,51,62,64,82,88,(101)(102)(103). In dramatic contrast, for COHbA, the tertiary relaxation does not begin until several nanoseconds subsequent to photodissociation (48,57,58,(103)(104)(105)(106). Consequently, slowing down the relaxation will, in the case of Mb, eventually allow the unrelaxed photoproduct to persist to beyond nanoseconds, whereas for HbA, the photoproduct already persists beyond nanoseconds.…”

Section: Discussionmentioning

confidence: 99%

Spectroscopically and Kinetically Distinct Conformational Populations of Sol-Gel-encapsulated Carbonmonoxy Myoglobin

Samuni

Dantsker

Khan

et al. 2002

Journal of Biological Chemistry

108

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We have used sol-gel encapsulation protocols to trap kinetically and spectroscopically distinct conformational populations of native horse carbonmonoxy myoglobin. The method allows for direct comparison of functional and spectroscopic properties of equilibrium and non-equilibrium populations under the same temperature and viscosity conditions. The results implicate tertiary structure changes that include the proximal heme environment in the mechanism for population-specific differences in the observed rebinding kinetics. Differences in the resonance Raman frequency of (Fe-His), the iron-proximal histidine stretching mode, are attributed to differences in the positioning of the F helix. For myoglobin, the degree of separation between the F helix and the heme is assigned as the conformational coordinate that modulates both this frequency and the innermost barrier controlling CO rebinding. A comparison with the behavior of encapsulated derivatives of human adult hemoglobin indicates that these CO binding-induced conformational changes are qualitatively similar to the tertiary changes that occur within both the R and T quaternary states. Protein-specific differences in the time scale for the proposed F helix relaxation are attributed to variations in the intra-helical hydrogen bonding patterns that help stabilize the position of the F helix. Myoglobin (Mb)1 continues to be used as a model protein system for investigations into how structure, dynamics, and reactivity interconnect to give rise to functionality. Recently there has been a renewed interest in myoglobin based on several new developments. From a functional point of view there are indications and suggestions that, apart from its physiological importance in facilitating oxygen diffusion, myoglobin has functions arising from its ability to participate in catalytic multisubstrate reactions involving such molecules as NO, O 2 , and H 2 O 2 (1-3). In addition the presence of apolar intra-protein substrate docking sites (the so-called Xe cavities) (4, 5) have recently been linked both to these newly proposed functions and to the kinetic patterns associated with geminate and bimolecular ligand binding (3, 6 -13).These new developments highlight fundamental biophysical issues that have not been fully addressed despite the extensive research effort that has been directed toward myoglobin. The issue that we address in this work relates to ligand reactivity as a function of conformation. Several studies show that myoglobin can adopt different tertiary conformations. In particular there is evidence that the equilibrium distribution of tertiary conformations is different for the deoxy (ferrous five coordinate) and CO derivatives of Mb. X-ray crystallographic studies show that there is a small clam shell-like rotation of the E and F helices in going from deoxy to COMb (14) as well as adjustments in the positioning of residues in the distal heme pocket (8 -10, 15, 16) that may or may not be related to the clam shell motion. Recent time-resolved x-ray crystallographic stud...

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“…Previous transient absorption studies showed that the CO photo-release from the fully ligated R-state Hb is followed by three relaxations with lifetimes of 50 ns, 1 µs, and 20 µs that were assigned to the unimolecular geminate rebinding, the tertiary structural relaxation, and the R→T quaternary change, respectively (Goldbeck et al, 1996). The geminate rebinding occurs too fast to be resolved by the PAC detector used in this study, whereas the 20 µs R→T transition, which strongly depends on the extent of heme ligation, is too slow to be resolved in PAC measurements.…”

Section: Discussionmentioning

confidence: 99%

“…Since this relaxation was observed as a small perturbation of the deoxy-Soret band (Goldbeck et al, 1996), it may reflect the structural relaxation localized within the vicinity of the heme binding pocket, which does not lead to measurable volume and enthalpy changes.…”

Section: Discussionmentioning

confidence: 99%

Conformational Dynamics Associated with Ligand Binding to Vertebrate Hexa-coordinate Hemoglobins

Astudillo¹

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Allosteric Intermediates in Hemoglobin. 2. Kinetic Modeling of HbCO Photolysis^,

Cited by 44 publications

References 42 publications

The Monod-Wyman-Changeux allosteric model accounts for the quaternary transition dynamics in wild type and a recombinant mutant human hemoglobin

The Monod-Wyman-Changeux allosteric model accounts for the quaternary transition dynamics in wild type and a recombinant mutant human hemoglobin

Spectroscopically and Kinetically Distinct Conformational Populations of Sol-Gel-encapsulated Carbonmonoxy Myoglobin

Conformational Dynamics Associated with Ligand Binding to Vertebrate Hexa-coordinate Hemoglobins

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Allosteric Intermediates in Hemoglobin. 2. Kinetic Modeling of HbCO Photolysis,

Cited by 44 publications

References 42 publications

The Monod-Wyman-Changeux allosteric model accounts for the quaternary transition dynamics in wild type and a recombinant mutant human hemoglobin

The Monod-Wyman-Changeux allosteric model accounts for the quaternary transition dynamics in wild type and a recombinant mutant human hemoglobin

Spectroscopically and Kinetically Distinct Conformational Populations of Sol-Gel-encapsulated Carbonmonoxy Myoglobin

Conformational Dynamics Associated with Ligand Binding to Vertebrate Hexa-coordinate Hemoglobins

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Allosteric Intermediates in Hemoglobin. 2. Kinetic Modeling of HbCO Photolysis^,