Mechanisms of ligand binding to pentacoordinate protoheme

Olson, John S.; McKinnie, Russell E.; Mims, Martha P.; White, Dabney K.

doi:10.1021/ja00344a019

Cited by 46 publications

(43 citation statements)

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“…, which is close to the diffusion limit (32,38,51,61 , effectively blocking the E7 channel, and there is a roughly monotonic decrease in the rate of NO binding with increasing size of the E7 side chain for other mutants. Scott et al (17) carried out a much more extensive mutagenesis mapping study of Mb using 90 mutants at 27 different positions, and their results confirmed quantitatively the E7 gate mechanism for ligand entry into Mb, which was originally developed using just E7 mutations (60).…”

Section: E7 Gate Appears To Be the Pathway For Ligand Entry Into Hba-mentioning

confidence: 51%

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Distal Histidine Stabilizes Bound O2 and Acts as a Gate for Ligand Entry in Both Subunits of Adult Human Hemoglobin

Birukou

Schweers²,

Olson

2010

Journal of Biological Chemistry

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100

174

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The role of the distal histidine in regulating ligand binding to adult human hemoglobin (HbA) was re-examined systematically by preparing His(E7) to Gly, Ala, Leu, Gln, Phe, and Trp mutants of both Hb subunits. Rate constants for O 2 , CO, and NO binding were measured using rapid mixing and laser photolysis experiments designed to minimize autoxidation of the unstable apolar E7 mutants. Replacing His(E7) with Gly, Ala, Leu, or Phe causes 20 -500-fold increases in the rates of O 2 dissociation from either Hb subunit, demonstrating unambiguously that the native His(E7) imidazole side chain forms a strong hydrogen bond with bound O 2 in both the ␣ and ␤ chains (⌬G His(E7)H-bond ≈ ؊8 kJ/mol). As the size of the E7 amino acid is increased from Gly to Phe, decreases in k O2 , In 1970, Perutz (1) proposed that the distal histidines located at the E7 helical positions, 3 ␣His-58 and ␤His-63, play crucial structural roles for regulating both the affinities and rates of O 2 binding to adult human hemoglobin (HbA). 4 These ideas were based on the suggestion by Pauling (2) that His(E7) could stabilize bound O 2 by donating a hydrogen bond to the partial negative charge on the superoxide-Fe(III)-like FeO 2 complex and on the idea by Perutz and Mathews (3) that the distal histidine could also be acting as gate for ligand entry and exit. Studies of model heme compounds and naturally occurring globins with His(E7) replacements suggested strongly that the distal histidine also plays a key role in discrimination between O 2 and CO binding (4 -9).The first mutagenesis studies on sperm whale Mb and human HbA reported that His(E7) to Gly mutations in ␣ subunits and Mb cause marked increases in the rates of O 2 dissociation and significant decreases in affinity, both of which indicate strong stabilization of the FeO 2 complex by proton donation from the wild-type His(E7) side chain (7, 10, 11). In addition, the association rate constants for O 2 and CO binding increased 5-10-fold. The latter results were interpreted in terms of the distal histidine gate mechanism, with the His(E7) to Gly mutation resulting in an open E7 channel. In contrast, neither the dissociation nor association rate constants for O 2 binding to the R state ␤Gly(E7) mutant of HbA appeared to increase significantly, implying no electrostatic stabilization of bound ligands by the native His(E7) in ␤ subunits and an already open gate or alternative pathway. These surprising kinetic results were explained by the first high resolution structure of human oxyhemoglobin published by Shaanan (12), in which the N⑀H atoms of distal histidine in ␤ subunits seemed to be further away from the bound O 2 atoms and pointing toward the heme plane.Between 1989 and 1999, our group and others constructed large libraries of mammalian Mb mutants as a model system for understanding the structural mechanisms of ligand binding to vertebrate globins involved in O 2 transport and storage. A detailed molecular mechanism for O 2 binding has emerged. Ligand entry into myoglobin occurs through t...

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Section: E7 Gate Appears To Be the Pathway For Ligand Entry Into Hba-mentioning

confidence: 51%

“…As shown in Table 3, 50,51) and hemoglobins with unhindered active sites (i.e. leghemoglobins (52) and Cerebratulus lacteus mini-globin (32)).…”

Section: His(e7) Regulates O 2 Binding and Release In Hbamentioning

confidence: 99%

Distal Histidine Stabilizes Bound O2 and Acts as a Gate for Ligand Entry in Both Subunits of Adult Human Hemoglobin

Birukou

Schweers²,

Olson

2010

Journal of Biological Chemistry

Self Cite

100

174

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“…In the case of myoglobin, P 50 equals the equilibrium dissociation constant, since only a single binding process occurs The data were taken from Olson et al [14] and Traylor et al [11][12][13] tochrome oxidase (F0.01 mM). Simple protoheme-imidazole complexes in apolar solvents show an affinity for reversible O 2 binding which is a least 100 times smaller than that for myoglobin (Table 1).…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, the FeCO complex is apolar and unlikely to interact strongly with polar amino acid side chains. Traylor and coworkers argued that the 50-fold increase in oxygen affinity observed when chelated protoheme is taken from benzene and put into myristyltrimethylammonium micelles is due to stabilization of the partial negative charge on the bound O 2 (Table 1) [11][12][13][14]. In this case, the favorable electrostatic interactions are less specific and come from either water bound to the micelles or the quaternary amine.…”

Section: Introductionmentioning

confidence: 99%

Myoglobin discriminates between O2, NO, and CO by electrostatic interactions with the bound ligand

1997

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Most biological substrates have distinctive sizes, shapes, and charge distributions which can be recognized specifically by proteins. In contrast, myoglobin must discriminate between the diatomic gases O 2 , CO, and NO which are apolar and virtually the same size. Selectivity occurs at the level of the covalent Feligand complexes, which exhibit markedly different bond strengths and electrostatic properties. By pulling a water molecule into the distal pocket, His64(E7) 1 inhibits the binding of all three ligands by a factor of F10 compared to that observed for protoheme-imidazole complexes in organic solvents. In the case of O 2 binding, this unfavorable effect is overcome by the formation of a strong hydrogen bond between His64(E7) and the highly polar FeO 2 complex. This favorable electrostatic interaction stabilizes the bound O 2 by a factor of F1000, and the net result is a 100-fold increase in overall affinity compared to model hemes or mutants with an apolar residue at position 64. Electrostatic interaction between FeCO and His64 is very weak, resulting in only a two-to three-fold stabilization of the bound state. In this case, the inhibitory effect of distal pocket water dominates, and a net fivefold reduction in K CO is observed for the wild-type protein compared to mutants with an apolar residue at position 64. Bound NO is stabilized Ftenfold by hydrogen bonding to His64. This favorable interaction with FeNO exactly compensates for the tenfold inhibition due to the presence of distal pocket water, and the net result is little change in K NO when the distal histidine is replaced with apolar residues. Thus, it is the polarity of His64 which allows discrimination between the diatomic gases. Direct steric hindrance by this residue plays a minor role as judged by: (1) the independence of K O 2 , K CO , and K NO on the size of apolar residues inserted at position 64, and (2) the observation of small decreases, not increases, in CO affinity when the mobility of the His64 side chain is increased. Val68(E11) does appear to hinder selectively the binding of CO. However, the extent is no more than a factor of 2-5, and much smaller than electrostatic stabilization of bound O 2 by the distal histidine.

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“…Diese Eigenschaft wurde in Versuchen zur Simulation der Wirkung von Kohlensäure-Anhydrase genutzt, dem Enzym, das für die Fixierung von Kohlendioxid und dessen physiologisch wichtige reversible Hydratation zu Hydrogencarbonat verantwortlich ist. [41] Die aktive Stelle im Enzym besteht aus einem Zinkion, das durch drei Histidin-Imidazolseitenketten und entweder ein Wassermolekül oder ein Hydroxidion koordiniert ist. Das ist eine Situation, für die man sich eine Simulation durch synthetische Liganden wünscht, um mehr über die Mechanismen der enzymatischen Prozesse zu erfahren.…”

Section: -Symmetrische Verbindungen Mit Pyridinringenunclassified

C3-Symmetrie in der asymmetrischen Katalyse und der chiralen Erkennung

Moberg

1998

Angewandte Chemie

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Mechanisms of ligand binding to pentacoordinate protoheme

Cited by 46 publications

References 0 publications

Distal Histidine Stabilizes Bound O2 and Acts as a Gate for Ligand Entry in Both Subunits of Adult Human Hemoglobin

Distal Histidine Stabilizes Bound O2 and Acts as a Gate for Ligand Entry in Both Subunits of Adult Human Hemoglobin

Myoglobin discriminates between O2, NO, and CO by electrostatic interactions with the bound ligand

C3-Symmetrie in der asymmetrischen Katalyse und der chiralen Erkennung

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