Solution 1H NMR investigation of the active site molecular and electronic structures of substrate-bound, cyanide-inhibited HmuO, a bacterial heme oxygenase from Corynebacterium diphtheriae

Yiming Li, Ray T. Syvitski, Grace C. Chu, Masao Ikeda-Saito, Gerd N. La Mar

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Abstract

The molecular structure and dynamic properties of the active site environment of HmuO, a heme oxygenase (HO) from the pathogenic bacterium Corynebacterium diphtheriae, have been investigated by 1H NMR spectroscopy using the human HO (hHO) complex as a homology model. It is demonstrated that not only the spatial contacts among residues and between residues and heme, but the magnetic axes that can be related to the direction and magnitude of the steric tilt of the FeCN unit are strongly conserved in the two HO complexes. The results indicate that very similar contributions of steric blockage of several meso positions and steric tilt of the attacking ligand are operative. A distal H-bond network that involves numerous very strong H-bonds and immobilized water molecules is identified in HmuO that is analogous to that previously identified in hHO (Li, Y., Syvitski, R. T., Auclair, K., Wilks, A., Ortiz de Montellano, P. R., and La Mar, G. N. (2002) J. Biol. Chem. 277, 33018-33031). The NMR results are completely consistent with the very recent crystal structure of the HmuO·substrate complex. The H-bond network/ordered water molecules are proposed to orient the distal water molecule near the catalytically key Asp136 (Asp140 in hHO) that stabilizes the hydroperoxy intermediate. The dynamic stability of this H-bond network in HmuO is significantly greater than in hHO and may account for the slower catalytic rate in bacterial HO compared with mammalian HO.

Original languageEnglish
Pages (from-to)6651-6663
Number of pages13
JournalJournal of Biological Chemistry
Volume278
Issue number9
DOIs
Publication statusPublished - 2003 Feb 28

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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