Human heme oxygenase oxidation of 5- and 15-phenylhemes.
Human heme oxygenase-1 (hHO-1) catalyzes the O2-dependent oxidation of heme to biliverdin, CO, and free iron. Previous work indicated that electrophilic addition of the terminal oxygen of the ferric hydroperoxo complex to the alpha-meso-carbon gives 5-hydroxyheme. Earlier efforts to block this reaction with a 5-methyl substituent failed, as the reaction still gave biliverdin IXalpha. Surprisingly, a 15-methyl substituent caused exclusive cleavage at the gamma-meso-rather than at the normal, unsubstituted alpha-meso-carbon. No CO was formed in these reactions, but the fragment cleaved from the porphyrin eluded identification. We report here that hHO-1 cleaves 5-phenylheme to biliverdin IXalpha and oxidizes 15-phenylheme at the alpha-meso position to give 10-phenylbiliverdin IXalpha. The fragment extruded in the oxidation of 5-phenylheme is benzoic acid, one oxygen of which comes from O2 and the other from water. The 2.29- and 2.11-A crystal structures of the hHO-1 complexes with 1- and 15-phenylheme, respectively, show clear electron density for both the 5- and 15-phenyl rings in both molecules of the asymmetric unit. The overall structure of 15-phenylheme-hHO-1 is similar to that of heme-hHO-1 except for small changes in distal residues 141-150 and in the proximal Lys18 and Lys22. In the 5-phenylheme-hHO-1 structure, the phenyl-substituted heme occupies the same position as heme in the heme-HO-1 complex but the 5-phenyl substituent disrupts the rigid hydrophobic wall of residues Met34, Phe214, and residues 26-42 near the alpha-meso carbon. The results provide independent support for an electrophilic oxidation mechanism and support a role for stereochemical control of the reaction regiospecificity.
Wang
Jinling
J
Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143-2280, USA.
Niemevz
Fernando
F
Lad
Latesh
L
Huang
Liusheng
L
Alvarez
Diego E
DE
Buldain
Graciela
G
Poulos
Thomas L
TL
de Montellano
Paul R Ortiz
PR
D000818:Animals; D001205:Ascorbic Acid / Q000737:chemistry; D019817:Benzoic Acid / Q000737:chemistry; D001664:Biliverdine / Q000737:chemistry; D002248:Carbon Monoxide / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D002853:Chromatography, Liquid; D018360:Crystallography, X-Ray; D004583:Electrons; D004952:Esters / Q000737:chemistry; D006418:Heme / Q000737:chemistry*; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry / Q000378:metabolism*; D006736:Horses; D006801:Humans; D007477:Ions; D008239:Lysine / Q000737:chemistry; D013058:Mass Spectrometry; D008715:Methionine / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D009211:Myoglobin / Q000031:analogs & derivatives* / Q000737:chemistry; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D013053:Spectrophotometry; D013237:Stereoisomerism; D013997:Time Factors; D014466:Ultraviolet Rays
D004952:Esters; D007477:Ions; D009211:Myoglobin; C055547:deoxymyoglobin; D006418:Heme; D002248:Carbon Monoxide; D019817:Benzoic Acid; D008715:Methionine; D006419:Heme Oxygenase (Decyclizing); D044925:Oxidoreductases Acting on CH-CH Group Donors; C019789:biliverdin reductase; D009251:NADPH-Ferrihemoprotein Reductase; D008239:Lysine; D001664:Biliverdine; D001205:Ascorbic Acid; D010100:Oxygen