2nya
From Proteopedia
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Crystal structure of the periplasmic nitrate reductase (NAP) from Escherichia coli
Overview
The Escherichia coli NapA (periplasmic nitrate reductase) contains a, [4Fe-4S] cluster and a Mo-bis-molybdopterin guanine dinucleotide cofactor., The NapA holoenzyme associates with a di-heme c-type cytochrome redox, partner (NapB). These proteins have been purified and studied by, spectropotentiometry, and the structure of NapA has been determined. In, contrast to the well characterized heterodimeric NapAB systems, ofalpha-proteobacteria, such as Rhodobacter sphaeroides and Paracoccus, pantotrophus, the gamma-proteobacterial E. coli NapA and NapB proteins, purify independently and not as a tight heterodimeric complex. This, relatively weak interaction is reflected in dissociation constants of 15, and 32 mum determined for oxidized and reduced NapAB complexes, respectively. The surface electrostatic potential of E. coli NapA in the, apparent NapB binding region is markedly less polar and anionic than that, of the alpha-proteobacterial NapA, which may underlie the weaker binding, of NapB. The molybdenum ion coordination sphere of E. coli NapA includes, two molybdopterin guanine dinucleotide dithiolenes, a protein-derived, cysteinyl ligand and an oxygen atom. The Mo-O bond length is 2.6 A, which, is indicative of a water ligand. The potential range over which the Mo(6+), state is reduced to the Mo(5+) state in either NapA (between +100 and -100, mV) or the NapAB complex (-150 to -350 mV) is much lower than that, reported for R. sphaeroides NapA (midpoint potential Mo(6+/5+) > +350 mV), and the form of the Mo(5+) EPR signal is quite distinct. In E. coli NapA, or NapAB, the Mo(5+) state could not be further reduced to Mo(4+). We then, propose a catalytic cycle for E. coli NapA in which nitrate binds to the, Mo(5+) ion and where a stable des-oxo Mo(6+) species may participate.
About this Structure
2NYA is a Single protein structure of sequence from Escherichia coli with SF4, 6MO and MGD as ligands. Active as Nitrate reductase, with EC number 1.7.99.4 Full crystallographic information is available from OCA.
Reference
Spectropotentiometric and structural analysis of the periplasmic nitrate reductase from Escherichia coli., Jepson BJ, Mohan S, Clarke TA, Gates AJ, Cole JA, Butler CS, Butt JN, Hemmings AM, Richardson DJ, J Biol Chem. 2007 Mar 2;282(9):6425-37. Epub 2006 Nov 27. PMID:17130127
Page seeded by OCA on Wed Nov 21 12:59:00 2007
