Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C1832526 (PCC)
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Two isoforms of a heme oxygenase gene, ho1 and ho2, with 51% identity in amino acid sequence have been identified in the cyanobacterium Synechocystis sp. PCC 6803. Isoform-1, Syn HO-1, has been characterized, while isoform-2, Syn HO-2, has not. In this study, a full-length ho2 gene was cloned using synthetic DNA and Syn HO-2 was demonstrated to be highly expressed in Escherichia coli as a soluble, catalytically active protein. Like Syn HO-1, the purified Syn HO-2 bound hemin stoichiometrically to form a heme-enzyme complex and degraded heme to biliverdin IXalpha, CO and iron in the presence of reducing systems such as NADPH/ferredoxin reductase/ferredoxin and sodium ascorbate. The activity of Syn HO-2 was found to be comparable to that of Syn HO-1 by measuring the amount of bilirubin formed. In the reaction with hydrogen peroxide, Syn HO-2 converted heme to verdoheme. This shows that during the conversion of hemin to alpha-meso-hydroxyhemin, hydroperoxo species is the activated oxygen species as in other heme oxygenase reactions. The absorption spectrum of the hemin-Syn HO-2 complex at neutral pH showed a Soret band at 412 nm and two peaks at 540 nm and 575 nm, features observed in the hemin-Syn HO-1 complex at alkaline pH, suggesting that the major species of iron(III) heme iron at neutral pH is a hexa-coordinate low spin species. Electron paramagnetic resonance (EPR) revealed that the iron(III) complex was in dynamic equilibrium between low spin and high spin states, which might be caused by the hydrogen bonding interaction between the distal water ligand and distal helix components. These observations suggest that the structure of the heme pocket of the Syn HO-2 is different from that of Syn HO-1.
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PMID:Protein expressed by the ho2 gene of the cyanobacterium Synechocystis sp. PCC 6803 is a true heme oxygenase. Properties of the heme and enzyme complex. 1569 34

Phycobiliproteins, light-harvesting proteins in cyanobacteria, red algae, and cryptophytes, contain phycobilin pigments. Phycobilins are synthesized from biliverdin, which is produced by the oxidative cleavage of the heme porphyrin ring catalyzed by heme oxygenase (HO). Two paralogs of ho (ho1 and ho2) have been identified in the genome of the cyanobacterium, Synechocystis sp. PCC 6803. The recombinant proteins of both paralogs (Syn HO-1 and Syn HO-2) possess in vitro heme degradation activity. We have determined the crystal structures of Syn HO-2 in complex with heme (heme-Syn HO-2) and its reduced and NO bound forms. The heme-Syn HO-2 crystal was a nonmerohedral twin, and detwinned diffraction data were used to refine the structure. Although heme-Syn HO-2 shares common folding with other HOs, the C-terminal segment is ordered and turns back to the heme-binding side. Gel-filtration chromatography analysis and molecular packing in the crystal indicate that heme-Syn HO-2 forms a homodimer, in which the C-terminal ordered segments interact with each other. Because Syn HO-2 is a monomer in the apo state, the dimeric interaction may aid in the selection of the reducing partner but likely does not interfere with heme binding. The heme iron is coordinated by a water molecule in the ferric form, but the distal water is absent in the ferrous form. In all of the Syn HO-2 structures, several water molecules form a hydrogen-bond network at the distal hemepocket, which is involved in HO activity. Upon NO binding, the side-chain conformation of Tyr 156 changes. Tyr 156 is located at the hydrophobic cluster, which interrupts the possible H(+) pathway from the molecular surface to the hemepocket. Thus, Tyr 156 may function as a H(+) shuttle by changing conformation.
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PMID:Crystal structure of dimeric heme oxygenase-2 from Synechocystis sp. PCC 6803 in complex with heme. 1576 54