Coupling of the Distal Hydrogen Bond Network to the Exogenous Ligand in Substrate-Bound, Resting State Human Heme Oxygenase
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- 作者：Dungeng Peng ; Hiroshi Ogura ; Wenfeng Zhu ; Li-Hua Ma ; John P. Evans ; Paul R. Ortiz de Montellano ; Gerd N. La Mar
- 刊名：Biochemistry
- 出版年：2009
- 出版时间：December 1, 2009
- 年：2009
- 卷：48
- 期：47
- 页码：11231-11242
- 全文大小：1119K
- 年卷期：v.48,no.47(December 1, 2009)
- ISSN：1520-4995
文摘
Mammalian heme oxygenase (HO) possesses catalytically implicated distal ordered water molecules within an extended H-bond network, with one of the ordered water molecules (#1) providing a bridge between the iron-coordinated ligand and the catalytically critical Asp140, that, in turn, serves as an acceptor for the Tyr58 OH H-bond. The degree of H-bonding by the ligated water molecule and the coupling of this water molecule to the H-bond network are of current interest and are herein investigated by 1H NMR. Two-dimensional NMR allowed sufficient assignments to provide both the H-bond strength and hyperfine shifts, the latter of which were used to quantify the magnetic anisotropy in both the ferric high-spin aquo and low-spin hydroxo complexes. The anisotropy in the aquo complex indicates that the H-bond donation to water #1 is marginally stronger than in a bacterial HO, while the anisotropy for the hydroxo complex reveals a conventional (dxz, dyz)1 ground state indicative of only moderate to weak H-bond acceptance by the ligated hydroxide. Mapping out the changes of the H-bond strengths in the network during the ligated water → hydroxide conversion by correcting for the effects of magnetic anisotropy reveals a very substantial change in H-bond strength for Tyr58 OH and lesser effects on nearby H-bonds. The effect of pH on the H-bonding network in human HO is much larger and transmitted much further from the iron than in a pathogenic bacterial HO. The implications for the HO mechanism of the H-bond of Tyr58 to Asp140 are discussed.