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| {{STRUCTURE_1nir| PDB=1nir | SCENE= }} | | {{STRUCTURE_1nir| PDB=1nir | SCENE= }} |
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| '''OXYDIZED NITRITE REDUCTASE FROM PSEUDOMONAS AERUGINOSA'''
| | ===OXYDIZED NITRITE REDUCTASE FROM PSEUDOMONAS AERUGINOSA=== |
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| ==Overview==
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| BACKGROUND: Nitrite reductase from Pseudomonas aeruginosa (NiR-Pa) is a dimer consisting of two identical 60 kDa subunits, each of which contains one c and one d1 heme group. This enzyme, a soluble component of the electron-transfer chain that uses nitrate as a source of energy, can be induced by the addition of nitrate to the bacterial growth medium. NiR-Pa catalyzes the reduction of nitrite (NO2-) to nitric oxide (NO); in vitro, both cytochrome c551 and azurin are efficient electron donors in this reaction. NiR is a key denitrification enzyme, which controls the rate of the production of toxic nitric oxide (NO) and ultimately regulates the release of NO into the atmosphere. RESULTS: The structure of the orthorhombic form (P2(1)2(1)2) of oxidized NiR-Pa was solved at 2.15 A resolution, using molecular replacement with the coordinates of the NiR from Thiosphaera pantotropha (NiR-Tp) as the starting model. Although the d1-heme domains are almost identical in both enzyme structures, the c domain of NiR-Pa is more like the classical class I cytochrome-c fold because it has His51 and Met88 as heme ligands, instead of His17 and His69 present in NiR-Tp. In addition, the methionine-bearing loop, which was displaced by His17 of the NiR-Tp N-terminal segment, is back to normal in our structure. The N-terminal residues (5/6-30) of NiR-Pa and NiR-Tp have little sequence identity. In Nir-Pa, this N-terminal segment of one monomer crosses the dimer interface and wraps itself around the other monomer. Tyr10 of this segment is hydrogen bonded to an hydroxide ion--the sixth ligand of the d1-heme Fe, whereas the equivalent residue in NiR-Tp, Tyr25, is directly bound to the Fe. CONCLUSIONS: Two ligands of hemes c and d1 differ between the two known NiR structures, which accounts for the fact that they have quite different spectroscopic and kinetic features. The unexpected domain-crossing by the N-terminal segment of NiR-Pa is comparable to that of 'domain swapping' or 'arm exchange' previously observed in other systems and may explain the observed cooperativity between monomers of dimeric NiR-Pa. In spite of having similar sequence and fold, the different kinetic behaviour and the spectral features of NiR-Pa and NiR-Tp are tuned by the N-terminal stretch of residues. A further example of this may come from another NiR, from Pseudomonas stutzeri, which has an N terminus very different from that of the two above mentioned NiRs.
| | The line below this paragraph, {{ABSTRACT_PUBMED_9331415}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 9331415 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_9331415}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Nitrite reductase]] | | [[Category: Nitrite reductase]] |
| [[Category: Pseudomonas aeruginosa]] | | [[Category: Pseudomonas aeruginosa]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 02:34:58 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Jul 27 20:57:50 2008'' |
