Replacement of the distal glycine 139 transforms human heme oxygenase-1 into a peroxidase.
The human heme oxygenase-1 crystal structure suggests that Gly-139 and Gly-143 interact directly with iron-bound ligands. We have mutated Gly-139 to an alanine, leucine, phenylalanine, tryptophan, histidine, or aspartate, and Gly-143 to a leucine, lysine, histidine, or aspartate. All of these mutants bind heme, but absorption and resonance Raman spectroscopy indicate that the water coordinated to the iron atom is lost in several of the Gly-139 mutants, giving rise to mixtures of hexacoordinate and pentacoordinate ligation states. The active site perturbation is greatest when large amino acid side chains are introduced. Of the Gly-139 mutants investigated, only G139A catalyzes the NADPH-cytochrome P450 reductase-dependent oxidation of heme to biliverdin, but most of them exhibit a new H(2)O(2)-dependent guaiacol peroxidation activity. The Gly-143 mutants, all of which have lost the water ligand, have no heme oxygenase or peroxidase activity. The results establish the importance of Gly-139 and Gly-143 in maintaining the appropriate environment for the heme oxygenase reaction and show that Gly-139 mutations disrupt this environment, probably by displacing the distal helix, converting heme oxygenase into a peroxidase. The principal role of the heme oxygenase active site may be to suppress the ferryl species formation responsible for peroxidase activity.
Liu
Y
Y
Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, California 94143-0446, USA.
Koenigs Lightning
L
L
Huang
H
H
Moënne-Loccoz
P
P
Schuller
D J
DJ
Poulos
T L
TL
Loehr
T M
TM
Ortiz de Montellano
P R
PR
D005998:Glycine / Q000378:metabolism*; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D051547:Heme Oxygenase-1; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D008565:Membrane Proteins; D016296:Mutagenesis; D010544:Peroxidases / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D013059:Spectrum Analysis, Raman
D008565:Membrane Proteins; D011994:Recombinant Proteins; D006861:Hydrogen Peroxide; D010544:Peroxidases; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D005998:Glycine