Blue copper proteins rusticyanin

This topic has been reviewed by Ingledew (55). The major components of the respiratory chain for T. ferrooxidans are a cytochrome oxidase of the Ci type, cytochromes c, and the blue copper protein rusticyanin. Initial electron transfer from Fe(II) to a cellular component takes place at the outer surface of the plasma membrane in the periplasmic space. The rate of electron transfer from Fe(II) to rusticyanin is too slow for rusticyanin to serve as the initial electron acceptor. Several proposals have been made for the primary site of iron oxidation. Ingledew (56) has suggested that the Fe(II) is oxidized by Fe(III) boimd to the cell wall the electron then moves rapidly through the polynuclear Fe(III) complex to rusticyanin or an alternative electron acceptor. Other proposals for the initial electron acceptor include a three-iron-sulfur cluster present in a membrane-bound Fe(II) oxidoreductase (39, 88), a 63,000 molecular weight Fe(II)-oxidizing enzyme isolated from T. ferrooxidans (40), and an acid-stable cytochrome c present in crude extracts of T. ferrooxidans (14). 

Ronk M, Shively JE, Shute EA, Blake RC Jr (1991) Amino acid sequence of the blue copper protein rusticyanin from Thiobacillus ferrooxidans. Biochemistry 30 9435-9442 Rothfus JA, Smith EL (1965) Amino acid sequence of rhesus monkey heart cytochrome c. J Biol Chem 240 4277-4283... 

The structural studies on amicyanin from P. versutus show that the protein consists of nine B-strands that form into two antiparallel /3-sheets, giving the molecule an overall structural motif known as a /3-sandwich (see Fig. 4). This overall topology is very similar to that of other structurally characterized cupredoxins, with the homology to plastocyanin being greatest (87). The only notable difference between amicyanin and most other cupredoxin structures is the presence of a 21-residue N-tereminal extension that forms an extra /8-strand in the structure. The recently published structural studies (95, 96) on the type 1 blue copper protein rusticyanin show that it, too, possesses an... 

The first class is cupredoxins—single-domain blue copper proteins composed of only one BCB domain. These proteins include plastocyanin, azurin, pseudoazurin, amicyanin, auracyanins, rusticyanin, halocyanin, and sulfocyanin (see Section IV). Plantacyanin of the phytocyanin family (Section V), subunit II of the cytochrome c oxidase, and the recently characterized nitrosocyanin also fall into this class. The last two are single BCB domain polypeptides closely related structurally to cupredoxins, but harboring, respectively, a binuclear copper site known as CuA and a novel type of copper-binding site called red (see Sections IX and X). 

Rusticyanin has a high reduction potential (680 mV), which is similar to that for the Type 1 Cu center in fungal as opposed to tree laccase (785 mV) (73). This trend is so far unexplained. From the sequence and EXAFS studies, His-Cys-His-Met coordination is a reasonable possibility for rusticyanin (55). It may well be that the reduction potential is determined by effects of a polypeptide backbone on Cu—S(Cys) and Cu—S(Met) bond distances and the Cu ligand field (74). If this is the case, however, rusticyanin would be expected to have one or both Cu—S distances shorter than in other blue copper proteins, which is not borne out by information from EXAFS (Table IV). A further possibility that the Cu(I) form is three-coordinate, as in the case of plasto-cyanin at low pH (Fig. 2), has no strong support at present (75). 

Rusticyanin is an abundant, highly stable periplasmic blue copper protein (e.g., Cobley and Haddock 1975 Jedlicki et al. 1986 Ronk et al. 1991 Nunzi et al. 1993 Blake et al. 1993). Studies of rusticyanin include kinetic competence in the iron oxidation reaction (Blake and Shute 1994), identification of a His ligand to the copper center (Casimiro et al. 1995), a solution NMR structure (Botuyan et al. 1996), and a high-resolution X-ray structure (Walter et al. 1996). Rusticyanin forms a complex with new c-type heme cytochrome in iht A. ferrooxidans electron transport chain (Giudici-Orticoni et al. 2000). 

Cobley JG (1984) Oxidation of nitrite and formate in Nitrobacter membrane preparations evidence that both reactions are catalyzed by the same enzyme. In Strohl WR, Tuovinen OH (eds) Microbial chemoautotrophy. Ohio State University Press, Columbus, pp 169-183 Cobley JG, Haddock BA (1975) The respiratory chain of Thiobacillus ferrooxidans reduction of cytochrome by Fe2+ and preliminary characterization of rusticyanin, a novel blue copper protein. FEBS Eett 60 29-33... 

Corbett CM, Ingledew WJ (1987) Is Fe3+/Fe2+ cycling an intermediate in sulphur oxidation by Thiobacillus ferrooxidans FEMS Microbiol Eett 41 1-6 Cox JC, Boxer DH (1978) The purification and some properties of rusticyanin, a blue copper protein involved in iron (II) oxidation from Thiobacillus ferro-oxidans. Biochem J 174 497-502... 

Nunzi F, Woudstra M, Compese D, Bonicel J, Morin D, Bruschi M (1993) Amino-acid sequence of rusticyanin from Thiobacillus ferrooxidans and its comparison with other blue copper proteins. Biochim Biophys Acta 1162 28-34... 

Rusticyanin (Rc), a member of blue copper proteins (BCP) which are relatively small, soluble electron-transfer proteins. Rc possesses a -barrel structure and is arranged in a so-caUed Greek key topology. It shows the highest redox potential (680 mV) of the BCP family, and is particularly efficient in stabilizing the copper (I) ion [F. Nunzi et al., Biochem. Biophys. Res. Com-mun. 1994, 203, 1655 L. A. Alcaraz et al.. Protein Sci. 2005, 14,1710]. 

Several copper enzymes will be discussed in detail in subsequent sections of this chapter. Information about major classes of copper enzymes, most of which will not be discussed, is collected in Table 5.1 as adapted from Chapter 14 of reference 49. Table 1 of reference 4 describes additional copper proteins such as the blue copper electron transfer proteins stellacyanin, amicyanin, auracyanin, rusticyanin, and so on. Nitrite reductase contains both normal and blue copper enzymes and facilitates the important biological reaction NO) — NO. Solomon s Chemical Reviews article4 contains extensive information on ligand field theory in relation to ground-state electronic properties of copper complexes and the application of... 

The A. ferrooxidans oxidase catalyzes the oxidation of ferrocytochrome c-552(s) (14 kDa), ferrocytochrome c-552(m) (22.3 kDa) or ferrocytochrome c4, and ferrocytochrome c-550(m) (51 kDa). Although the oxidase also catalyzes the oxidation of the reduced form of rusticyanin, its Km for rusticyanin is fairly large (600 pM) (Kai et al., 1992 Yamanaka and Fukumori, 1995) while Kms of the oxidase for cytochromes c-552(s), c-552(m) and c-550(m) are 17, 2.2, and 4.2 jM, respectively. However, as the concentration of rusticyanin in the bacterial cells is considerably high, the copper protein can also be the electron donor for the oxidase in vivo. Although the oxidase shows a catalytic capability to oxidize molybdenum blue (Sugio et al 1992a), the catalysis is not limited to the A. ferrooxidans oxidase because some oxidases belonging to cytochrome aa3 also show such activity (Kai et al., 1992). 

Fig. 16 a, b. Folding pattern of the small blue protein rusticyanin. The protein consists of thirteen /1-strands a ribbon model - the copper ion is represented by the blue circle [112] b disposition of ligands and spatially close side-chains in the copper site of one of the solution structures of Cu(I) rusticyanin. [112a] with permission... 

Fig. 37. Phylogenetic family tree of the four small blue protein families. The roots as well as the branching points to auracyanin, rusticyanin, halocyanin, and umecyanin are currently not known. Plastocyanin occurs in bacteria as well as in eukaryotes. Ascorbate oxidase was used as reference protein in creating the diagram. The plant allergen Ra3 is a non-copper protein. Halocyanin is currently the only known archaeate copper protein. Adapted from Ryden and Hunt 1993 [71]...

Rusticyanin is a copper-containing blue protein. It was first purified by Cox and Boxer (1978). The author and his colleagues purified it to a homogeneous state and... 

Small blue proteins are involved in various biochemical processes. Where their physiological function is known, it is that of single-electron transport proteins. The range of their redox potentials reaches from +183 mV (Halocyanin [18], + 184 mV Stellacyanin [68] to 680 mV (Rusticyanin [68, 69]) as compared to Cu2+/Cu+, E° = +153 mV. Very few redox proteins function in this range. This feature, and their characteristic blue color are the product of the type 1 copper center, the only redox-active group in these proteins. During electron... 

Rusticyanin s type 1 copper center with its ligands His 85, Cys 138, His 143, and Met 148 resembles those of the other small blue proteins. Although its tertiary structure is a /1-meander, there are distinct differences between the amino acid folding patterns of rusticyanin and the other small blue proteins. Plastocyanin contains 8 [22, 71], amicyanin 9 [20, 78], and rusticyanin 13 / -strands, respectively [112] (Fig. 16). 

---