Heme regulatory motifs in heme oxygenase-2 form a thiol/disulfide redox switch that responds to the cellular redox state.
Heme oxygenase (HO) catalyzes the rate-limiting step in heme catabolism to generate CO, biliverdin, and free iron. Two isoforms of HO have been identified in mammals: inducible HO-1 and constitutively expressed HO-2. HO-1 and HO-2 share similar physical and kinetic properties but have different physiological roles and tissue distributions. Unlike HO-1, which lacks cysteine residues, HO-2 contains three Cys-Pro signatures, known as heme regulatory motifs (HRMs), which are known to control processes related to iron and oxidative metabolism in organisms from bacteria to humans. In HO-2, the C-terminal HRMs constitute a thiol/disulfide redox switch that regulates affinity of the enzyme for heme (Yi, L., and Ragsdale, S. W. (2007) J. Biol. Chem. 282, 20156-21067). Here, we demonstrate that the thiol/disulfide switch in human HO-2 is physiologically relevant. Its redox potential was measured to be -200 mV, which is near the ambient intracellular redox potential. We expressed HO-2 in bacterial and human cells and measured the redox state of the C-terminal HRMs in growing cells by thiol-trapping experiments using the isotope-coded affinity tag technique. Under normal growth conditions, the HRMs are 60-70% reduced, whereas oxidative stress conditions convert most (86-89%) of the HRMs to the disulfide state. Treatment with reductants converts the HRMs largely (81-87%) to the reduced dithiol state. Thus, the thiol/disulfide switch in HO-2 responds to cellular oxidative stress and reductive conditions, representing a paradigm for how HRMs can integrate heme homeostasis with CO signaling and redox regulation of cellular metabolism.
Yi
Li
L
Departments of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Jenkins
Paul M
PM
Leichert
Lars I
LI
Jakob
Ursula
U
Martens
Jeffrey R
JR
Ragsdale
Stephen W
SW
D020816:Amino Acid Motifs; D002460:Cell Line; D004220:Disulfides / Q000378:metabolism*; D004926:Escherichia coli; D006418:Heme / Q000378:metabolism*; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D013438:Sulfhydryl Compounds / Q000378:metabolism*
D004220:Disulfides; D013438:Sulfhydryl Compounds; D006418:Heme; D006419:Heme Oxygenase (Decyclizing); C105245:heme oxygenase-2