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Thr-E11 regulates O-2 affinity in Cerebratulus lacteus mini-hemoglobin
Pesce, A.; Nardini, M.; Ascenzi, P.; Geuens, E.; Dewilde, S.; Moens, L.; Bolognesi, M.; Riggs, A.F.; Hale, A.; Deng, P.; Nienhaus, G.U.; Olson, J.S.; Nienhaus, K. (2004). Thr-E11 regulates O-2 affinity in Cerebratulus lacteus mini-hemoglobin. J. Biol. Chem. 279(32): 33662-33672. https://dx.doi.org/10.1074/jbc.M403597200
In: Journal of Biological Chemistry. American Society for Biochemistry and Molecular Biology: Baltimore, etc.. ISSN 0021-9258; e-ISSN 1083-351X, meer
Peer reviewed article  
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  • Pesce, A.
  • Nardini, M.
  • Ascenzi, P.
  • Geuens, E.
  • Dewilde, S., meer
  • Moens, L.
  • Bolognesi, M.
  • Riggs, A.F.
  • Hale, A.
  • Deng, P.
  • Nienhaus, G.U.
  • Olson, J.S.
  • Nienhaus, K.
Abstract
    The mini-hemoglobin from Cerebratulus lacteus (CerHb) belongs to a class of globins containing the polar Tyr-B10/Gln-E7 amino acid pair that normally causes low rates of O2 dissociation and ultra-high O2 affinity, which suggest O2 sensing or NO scavenging functions. CerHb, however, has high rates of O2 dissociation (kO2 = 200-600 s-1) and moderate O2 affinity (KO2 ≈1 μm-1) as a result of a third polar amino acid in its active site, Thr-E11. When Thr-E11 is replaced by Val, kO2 decreases 1000-fold and KO2 increases 130-fold at pH 7.0, 20 °C. The mutation also shifts the stretching frequencies of both heme-bound and photodissociated CO, indicating marked changes of the electrostatic field at the active site. The crystal structure of Thr-E11 → Val CerHbO2 at 1.70 Å resolution is almost identical to that of the wild-type protein (root mean square deviation of 0.12 Å). The dramatic functional and spectral effects of the Thr-E11 → Val mutation are due exclusively to changes in the hydrogen bonding network in the active site. Replacing Thr-E11 with Val “frees” the Tyr-B10 hydroxyl group to rotate toward and donate a strong hydrogen bond to the heme-bound ligand, causing a selective increase in O2 affinity, a decrease of the rate coefficient for O2 dissociation, a 40 cm-1 decrease in νCO of heme-bound CO, and an increase in ligand migration toward more remote intermediate sites.
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