Stellacyanin is a member of the blue or type I copper protein family. This family of copper proteins is generally involved in electron transfer reactions with the Cu center transitioning between the oxidized Cu(II) form and the reduced Cu(I) form. Stellacyanin is ubiquitous among vascular seed plants. [1]
Stellacyanin’s spectroscopic properties help us differentiate it from plastocyanin, which is another monocopper blue protein found in plants. [2] It is a 20kDa protein whose structure is made up of beta strands forming two beta sheets to form a Greek key beta barrel with variable alpha helical structure. The copper binding domain of the protein is located at the amino-terminal end, while the carboxyl-terminal end is rich in hydroxyproline and serine residues, typical of proteins associated with cell walls of plants. In addition, it is also heavily glycosylated. [1] [3] [4] The copper is tetrahedrally coordinated by a cysteine, 2 histidines, and a glutamine residue. The glutamine residue takes place of a methionine ligand typically found in other blue copper proteins. [1] In addition, electron transfer rates for stellacyanin are faster than for other type I copper proteins suggesting stellacyanin is more solvent accessible at the active site. [1] The exact function of stellacyanin is unknown. However, given the fact that type I copper proteins are involved in electron transfer and stellacyanin appears to be associated with the plant cell wall, it is suggested that it is involved in oxidative cross-linking reactions to build polymeric material making up the cell wall. [1] [3] Cell wall structural glycoproteins contain hydroxyproline and serine-rich sequence domains which are found in stellacyanins. [2]
Stellacyanins are characterized by their uniquely low redox potentials, as low as +180 mv and reach up to +280 mV. Other blue copper protein redox potentials start around +310 mV and reach up to +680 mV. [2] A mutant cucumber stellacyanin was created by replacing the glutamine axial ligand (a ligand which all other blue proteins contain) with a methionine (Q99M) and purified. This was achieved through Polymerase Chain Reaction (PCR). The mutated stellacyanin calculated redox potential was +420 mV, which much higher than the redox potential of the stellacyanin found in nature (without methionine) at +260 mV. Stellacyanins are most involved in redox reactions of plants that take place during a defense response, and formation of lignin. [2]
Redox is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state.
Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large proportion of all proteins are part of this category. For instance, at least 1000 human proteins contain zinc-binding protein domains although there may be up to 3000 human zinc metalloproteins.
In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate, the binding site, and residues that catalyse a reaction of that substrate, the catalytic site. Although the active site occupies only ~10–20% of the volume of an enzyme, it is the most important part as it directly catalyzes the chemical reaction. It usually consists of three to four amino acids, while other amino acids within the protein are required to maintain the tertiary structure of the enzymes.
A galvanic cell or voltaic cell, named after the scientists Luigi Galvani and Alessandro Volta, respectively, is an electrochemical cell in which an electric current is generated from spontaneous Oxidation-Reduction reactions. A common apparatus generally consists of two different metals, each immersed in separate beakers containing their respective metal ions in solution that are connected by a salt bridge or separated by a porous membrane.
Plastocyanin is a copper-containing protein that mediates electron-transfer. It is found in a variety of plants, where it participates in photosynthesis. The protein is a prototype of the blue copper proteins, a family of intensely blue-colored metalloproteins. Specifically, it falls into the group of small type I blue copper proteins called "cupredoxins".
DD-transpeptidase is a bacterial enzyme that catalyzes the transfer of the R-L-αα-D-alanyl moiety of R-L-αα-D-alanyl-D-alanine carbonyl donors to the γ-OH of their active-site serine and from this to a final acceptor. It is involved in bacterial cell wall biosynthesis, namely, the transpeptidation that crosslinks the peptide side chains of peptidoglycan strands.
Ferredoxins are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied to the "iron protein" first purified in 1962 by Mortenson, Valentine, and Carnahan from the anaerobic bacterium Clostridium pasteurianum.
In biochemistry, flavin adenine dinucleotide (FAD) is a redox-active coenzyme associated with various proteins, which is involved with several enzymatic reactions in metabolism. A flavoprotein is a protein that contains a flavin group, which may be in the form of FAD or flavin mononucleotide (FMN). Many flavoproteins are known: components of the succinate dehydrogenase complex, α-ketoglutarate dehydrogenase, and a component of the pyruvate dehydrogenase complex.
Copper proteins are proteins that contain one or more copper ions as prosthetic groups. Copper proteins are found in all forms of air-breathing life. These proteins are usually associated with electron-transfer with or without the involvement of oxygen (O2). Some organisms even use copper proteins to carry oxygen instead of iron proteins. A prominent copper proteins in humans is in cytochrome c oxidase (cco). The enzyme cco mediates the controlled combustion that produces ATP.
Nitrite reductase refers to any of several classes of enzymes that catalyze the reduction of nitrite. There are two classes of NIR's. A multi haem enzyme reduces NO2− to a variety of products. Copper containing enzymes carry out a single electron transfer to produce nitric oxide.
The transforming growth factor beta (TGFB) signaling pathway is involved in many cellular processes in both the adult organism and the developing embryo including cell growth, cell differentiation, cell migration, apoptosis, cellular homeostasis and other cellular functions. The TGFB signaling pathways are conserved. In spite of the wide range of cellular processes that the TGFβ signaling pathway regulates, the process is relatively simple. TGFβ superfamily ligands bind to a type II receptor, which recruits and phosphorylates a type I receptor. The type I receptor then phosphorylates receptor-regulated SMADs (R-SMADs) which can now bind the coSMAD SMAD4. R-SMAD/coSMAD complexes accumulate in the nucleus where they act as transcription factors and participate in the regulation of target gene expression.
Laccases are multicopper oxidases found in plants, fungi, and bacteria. Laccases oxidize a variety of phenolic substrates, performing one-electron oxidations, leading to crosslinking. For example, laccases play a role in the formation of lignin by promoting the oxidative coupling of monolignols, a family of naturally occurring phenols. Other laccases, such as those produced by the fungus Pleurotus ostreatus, play a role in the degradation of lignin, and can therefore be classed as lignin-modifying enzymes. Other laccases produced by fungi can facilitate the biosynthesis of melanin pigments. Laccases catalyze ring cleavage of aromatic compounds.
Cystathionine-β-synthase, also known as CBS, is an enzyme (EC 4.2.1.22) that in humans is encoded by the CBS gene. It catalyzes the first step of the transsulfuration pathway, from homocysteine to cystathionine:
Amicyanin is a type I copper protein that plays an integral role in electron transfer. In bacteria such as Paracoccus denitrificans, amicyanin is part of a three-member redox complex, along with methylamine dehydrogenase (MADH) and cytochrome c-551i.
Plastocyanin/azurin family of copper-binding proteins is a family of small proteins that bind a single copper atom and that are characterised by an intense electronic absorption band near 600 nm. The most well-known members of this class of proteins are the plant chloroplastic plastocyanins, which exchange electrons with cytochrome c6, and the distantly related bacterial azurins, which exchange electrons with cytochrome c551. This family of proteins also includes amicyanin from bacteria such as Methylobacterium extorquens or Paracoccus versutus that can grow on methylamine; auracyanins A and B from Chloroflexus aurantiacus; blue copper protein from Alcaligenes faecalis; cupredoxin (CPC) from Cucumis sativus (Cucumber) peelings; cusacyanin from cucumber; halocyanin from Natronomonas pharaonis, a membrane-associated copper-binding protein; pseudoazurin from Pseudomonas; rusticyanin from Thiobacillus ferrooxidans; stellacyanin from Rhus vernicifera ; umecyanin from the roots of Armoracia rusticana (Horseradish); and allergen Ra3 from ragweed. This pollen protein has evolutary relation to the above proteins, but seems to have lost the ability to bind copper. Although there is an appreciable amount of divergence in the sequences of all these proteins, the copper ligand sites are conserved.
Cytochromes c cytochromes, or heme-containing proteins, that have heme C covalently attached to the peptide backbone via one or two thioether bonds. These bonds are in most cases part of a specific Cys-X-X-Cys-His (CXXCH) binding motif, where X denotes a miscellaneous amino acid. Two thioether bonds of cysteine residues bind to the vinyl sidechains of heme, and the histidine residue coordinates one axial binding site of the heme iron. Less common binding motifs can include a single thioether linkage, a lysine or a methionine instead of the axial histidine or a CXnCH binding motif with n>2. The second axial site of the iron can be coordinated by amino acids of the protein, substrate molecules or water. Cytochromes c possess a wide range of properties and function as electron transfer proteins or catalyse chemical reactions involving redox processes. A prominent member of this family is mitochondrial cytochrome c.
Dioxygenases are oxidoreductase enzymes. Aerobic life, from simple single-celled bacteria species to complex eukaryotic organisms, has evolved to depend on the oxidizing power of dioxygen in various metabolic pathways. From energetic adenosine triphosphate (ATP) generation to xenobiotic degradation, the use of dioxygen as a biological oxidant is widespread and varied in the exact mechanism of its use. Enzymes employ many different schemes to use dioxygen, and this largely depends on the substrate and reaction at hand.
Azurin is a small, periplasmic, bacterial blue copper protein found in Pseudomonas, Bordetella, or Alcaligenes bacteria. Azurin moderates single-electron transfer between enzymes associated with the cytochrome chain by undergoing oxidation-reduction between Cu(I) and Cu(II). Each monomer of an azurin tetramer has a molecular weight of approximately 14kDa, contains a single copper atom, is intensively blue, and has a fluorescence emission band centered at 308 nm.
In bioinorganic chemistry, an entatic state is "a state of an atom or group which, due to its binding in a protein, has its geometric or electronic condition adapted for function." The term was coined by Bert Vallee and R. J. P. Williams, following work on the catalytic activity of carbonic anhydrase. These states are thought to enhance the chemistry of metal ions in biological catalysis.
Galactose oxidase is an enzyme that catalyzes the oxidation of D-galactose in some species of fungi.
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