Achromobacter cycloclastes

The blue protein from A. faecalis strain S-6, which was isolated as a requirement for transferring electrons to a copper-containing nitrite reductase, has since been shown to have sequence homology with proteins arbitrarily designated pseudoazurin by Ambler and Tobari (1985), from Achromobacter cycloclastes and from Pseudomonas AMI. [Pseudomonas AMI also produces amicyanin, which is the recipient of electrons from methylamine dehydrogenase, (see below)]. In A. cycloclastes reduced pseudoazurin donates electrons to a copper nitrite reductase (Liu et ai, 1986), as it does in A. faecalis. Ambler and Tobari (1985)... 

Hulse, C. L., and Averill, B. A. (1989). Evidence for a copper-nitrosyl intermediate in denitrification by the copper-containing nitrite reductase of Achromobacter cycloclastes. J. Am. Chem. Soc. Ill, 2322-2323. 

Iwasaki, N., Noji, S., and Shidara, S. (1975). Achromobacter cycloclastes nitrite reductase. The function of copper, amino acid composition, and ESR spectra. J. Biochem. (Tokyo) 78, 355-361. 

Jones, A. M., and Hollocher, T. C. (1993), Nitric oxide reductase from Achromobacter cycloclastes. Biochim. Biophys. Acta 1144, 359-366. 

Libby, E., and Averill, B. A. (1992). Evidence that the type 2 copper centers are the site of nitrite reduction by Achromobacter cycloclastes nitrite reductase. Biochem. Biophys. Res. Commun. 187, 1529-1535. 

The crystal structure of nitrite reductase (NiR) from Achromobacter cycloclastes was recently reported by Godden et al. (46). The protein contains both a type I and a type II copper site. The type I center has a distorted tetrahedral structure typical of type I copper, whereas the... 

Several copper-containing NiRs have been identified, but the most extensive structural and mechanistic studies have focused on the enzyme from Achromobacter cycloclastes (17-25). A 2.3-A resolution X-ray crystal structure for this NiR in its oxidized form at pH 5.2 has been reported (17), and a representation of the active site is shown in Figure 1. Each monomer in the trimeric protein contains two copper ions, one of which (Cu-1) is ligated to a cysteine, a methionine, and two histidine residues in a geometry similar to that of type 1 copper centers in proteins such as plastocyanin (26). The second type 2 copper ion in NiR (Cu-2) is only 12.5-A distant from the first and is bound to three histidine imidazoles (two from one monomer, the third from an associated subunit) and a fourth small ligand in an unusual tetrahedral arrangement. The... 

Figure 1. Schematic representation of the copper sites in nitrite reductase from Achromobacter cycloclastes (17).

Reversible protonation and dissociation of the exposed His ligand have been observed in several BCP in the reduced metal-bound state. Since this protonation renders the proteins inactive, it has been characterized thoroughly (Sykes, 1985, 1991). An active site of 4.9 was determined by NMR for Cu(I) spinach plastocyanin (Markley et al., 1975). The occurrence of this process was conhrmed later by the crystal structure of reduced poplar plastocyanin at low pH (Cuss et al., 1986). Similar equilibria have been characterized in Achromobacter cycloclastes pseudoa-zurin (pA a 4.6) (Dennison et al., 1994b) and in Thiobacillus versutus ami-cyanin (pA a 6.7) (Lommen et al., 1988). In the latter system a lineshape analysis revealed that this His residue, on protonation and detachment from the copper(I) ion, fluctuates between two conformers (Lommen and Canters, 1990). 

Figure 3 Electronic absorption (A) and magnetic circular dichroism (B) spectra of the Type 1 Cu site of Achromobacter cycloclastes nitrite reductase (a) and spinach plastocyanin (b). Absorption data were obtained at 120 K for nitrite reductase and at 25 K for plastocyanin. MCD spectra were obtained at 4.2 K. Gaussian resolution of bands in the absorption spectra is based on a simultaneous linear least-squares fit of Abs, MCD, and CD data for each. MCD data from 5000 to 8000 cm have been multiplied by a factor of 5. (Reprinted with permission from Ref. 22. 1996 American Chemical Society)...

Figure 11 (a) The organization of the nos cluster from Achromobacter cycloclastes and Paracoccus denitrificans. (h) The predicted locations of Nos proteins... 

Fig. 8. (a) Drawing of the trimer of nitrite reductase from Achromobacter cycloclastes. (b) Drawing of the interface between domain 1 (subunit A) and domain 2 of the adjacent symmetry-related molecule (subunit C) of nitrite reductase from A. cycloclastes. (c) Drawing of domain 1 and 3 of ascorbate oxidase. The type-1 copper is in domain 3 and the trinuclear copper center is between domain 1 and domain 3. The domains have an orientation similar to that of the corresponding domains of the nitrite reductase shown in b. The figure was produced by the RIBBON Program (S7). 

In 1985 the existence of two new classes of bacterial blue proteins, the pseudoazurins and amicyanins, was demonstrated (28). Sequence information is available for pseudoazurin from Pseudomonas AMI (28), Achromobacter cycloclastes (29), as well as A. faecalis, for which the structure has been determined (12). The name pseudoazurin rather than cupredoxin is used here. The sequence for amicyanin, also present in Pseudomonas AMI, has been reported, and that for amicyanin from Thiobacillus versutus is being determined. Preliminary X-ray crystallographic information has been reported for amicyanin from T. versutus (30). 

Iwasaki H, Matsubara T (1972) A nitrite reductase from Achromobacter cycloclastes. J Biochem 71 645-652... 

Until now, pseudoazurin has only been found in bacteria, e.g., in the denitrifying bacteria Alcaligenes faecalis and Achromobacter cycloclastes. It is the electron donor of the green copper-protein nitrite reductase which catalyses the reduction of nitrite (NO2) to nitrogen monoxide (NO) [86-89]. The physiological electron donor of pseudoazurin is as yet unknown [70]. Pseudoazurin has a molecular mass of approximately 13.5 kD and a chain length of about 123 amino acid residues [88]. The additional amino acids, as compared with plastocyanin, form the C-terminal end of the protein (Fig. 14). The pseudoazurins have redox potentials of about 230 mV [90,91]. 

Most proteins with type 1 copper centers are blue, although the nitrite reductases from Achromobacter cycloclastes, Alcaligenes faecalis, and Pseudomonas aureofaciens, are green [26,27]. This is probably caused by a distortion of the type 1 copper center, although the interrelation of distortion and absorption properties of the copper centers have not yet been clarified [27]. 

Figure 14. The 3D structure of CuNiR from Achromobacter cycloclastes (AcNiR). The protein backbone is shown together with the typel and type 2 copper ions and their ligands. Coordinates were taken from the PDB, code INDT.

Figure 42 Ribbon diagram of a monomer of nitrous oxide reductase from Achromobacter cycloclastes showing two domains, a C-terminai cupredoxin domain (ieft, in iighter shade) carrying the Cua center (dark biue spheres) and the N-terminai /3-propeiier domain (right, darker shade) with the cataiytic Cuz center in which copper and inorganic S ions are shown as iight biue and dark yeiiow spheres. Reproduced from R. R. Eady S. V. Antonyuk S. S. Hasnain, in Handbook of Metalloproteins, A. Messerschmidt, Ed. John Wiiey Sons Chichester, 2007 Voi. 4, pp 1-15 with permission from John Wiiey Sons.

A denitrifying nitrite reductase from Achromobacter cycloclastes and Ps. denitrificans is a copper protein, containing two moles copper per mole of protein (molecular weight 69 000). This reduces nitrite to nitrogen monoxide. 

Nitrite Reductase Achromobacter cycloclastes 458nm = 2200 Esssmn 1.800 1.22 rhombic (73) 2.56 278,279... 

The structures of the enzymes from Achromobacter cycloclastes Alcaligenes faecalis S6, " Alcaligenes xylosoxidans, and the soluble domain of NiR from N. gonorrhoeae have been determined. 

Nitrite reduction to nitric oxide is catalyzed by dissimilatory nitrite reductase. The enzymes purified from Alcaligenes faecalis (Iwasaki and Matsub-ara, 1971), Pseudomonas aeruginosa (Walker and Nicholas, 1961), andMj-crococcus denitrificans (Newton, 1969) have been shown to contain c d-type cytochrome. The nitrite reductase from Achromobacter cycloclastes does not... 

Adman ET, Godden JW, Turley S (1995) The structure of copper-nitrite reductase from achromobacter cycloclastes at five pH values, with NO-2 bound and with type 11 copper depleted. J Biol Chem 270 27458-27474... 

The following cry.stal structures were used poplar plasto-cyanin at 1.3 A resolution (PDB file IPLC). nitrite reducta.se from Achromobacter cycloclastes at 1.9 A resolution (PDB file INIC)," and cucumber basic protein from cucumber seedlings at 1.8 A resolution (PDB file 2CBP). ... 

The copper-containing nitrite reductases (Cu NiR s) also contain two distinct types of chromophore. The best characterized is that from Achromobacter cycloclastes, for which a 2.3 A resolution X-ray structure has been reported (12). The enzyme consists of an a3 trimer of 34.5 kDa subunits, each of which contains two copper atoms in distinct sites. One is an... 

Figure 8. Schematic drawing showing the structure and arrangement of copper centers in the Cu-containing nitrite reductase from Achromobacter cycloclastes.

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