title: Heme oxygenase-2 is activated by calcium-calmodulin.
abstract: The heme oxygenase family of enzymes catalyzes the metabolism of heme to biliverdin, ferrous iron, and carbon monoxide (CO). At least two isoforms exist, heme oxygenase-1 (HO1) and heme oxygenase-2 (HO2), which are encoded by separate genes. HO2 is selectively enriched in neurons, and substantial evidence suggests that HO2-derived CO functions as a neurotransmitter/neuromodulator. However, a molecular mechanism for the rapid activation of HO2 during neuronal activity has not been described. Through a yeast two-hybrid screen we identified calmodulin as a potential regulator of HO2 activity. Calmodulin binds with nanomolar affinity to HO2 in a calcium-dependent manner via a canonical 1-10 motif, resulting in a 3-fold increase in catalytic activity. Mutations within this motif block calmodulin binding and calcium-dependent stimulation of enzyme activity in vitro and in intact cells. The calcium mobilizing agents ionomycin and glutamate stimulate endogenous HO2 activity in primary cortical cultures, establishing in vivo relevance. Calcium-calmodulin provides a mechanism for rapid and transient activation of HO2 during neuronal activity.
authors.affiliation: Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Darren
authors.initials: D
authors.lastname: Boehning
authors.forename: Leela
authors.initials: L
authors.lastname: Sedaghat
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Sedlak
authors.forename: Solomon H
authors.initials: SH
authors.lastname: Snyder
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002248:Carbon Monoxide / Q000378:metabolism; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D004789:Enzyme Activation; D018698:Glutamic Acid / Q000494:pharmacology; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques
chemical_list: D002147:Calmodulin; D017931:DNA Primers; D007476:Ionophores; D018377:Neurotransmitter Agents; D011994:Recombinant Proteins; D018698:Glutamic Acid; D015759:Ionomycin; D002248:Carbon Monoxide; D006419:Heme Oxygenase (Decyclizing); C105245:heme oxygenase-2; D002118:Calcium