Rusticyanin (RCN) is a
copper protein with a type I copper center that plays an integral role in electron transfer.
It can be extracted from the
periplasm
The periplasm is a concentrated gel-like matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the ''periplasmic space'' in gram-negative bacteria. Using cryo-electron microscopy it has been found tha ...
of the
gram-negative bacterium Thiobacillus ferrooxidans (T. ferrooxidans), also known as
Acidithiobacillus ferrooxidans (At. ferrooxidans).
Rusticyanin is also found in the membrane-bound form in the surface of T. ferrooxidans. It is a part of an
electron transfer chain for
Fe(II)
In chemistry, iron(II) refers to the element iron in its +2 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe2+.
The adjective ferrous or the prefix ferro- is often used to spe ...
oxidation
Redox (reduction–oxidation, , ) 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 ...
.
Function
As T. ferrooxidans can grow aerobically at
pH values of 1.6 to 3.5, it obtains its energy for
chemolithotrophic
Lithotrophs are a diverse group of organisms using an inorganic substrate (usually of mineral origin) to obtain reducing equivalents for use in biosynthesis (e.g., carbon dioxide fixation) or energy conservation (i.e., ATP production) via aerob ...
growth on soluble ferrous ions.
Rusticyanin is involved in the respiratory oxidation of ferrous ions to ferric ions, producing three
protons for every ferrous ion oxidized. The mechanism of
electron transfer
Electron transfer (ET) occurs when an electron relocates from an atom or molecule to another such chemical entity. ET is a mechanistic description of certain kinds of redox reactions involving transfer of electrons.
Electrochemical processes ar ...
in the respiratory oxidation pathway of Fe
2+ in T. ferrooxidans is still unclear despite decades of research in this area. However, the involvement of rusticyanin in shuttling electrons from a
cytochrome c2 to another
cytochrome c4 during the oxidation of ferrous to ferric ions is experimentally shown. Rusticyanin is thought to shuttle
electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary partic ...
s from high
molecular weight
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
cytochrome via
cytochrome c552
Cytochromes are redox-active proteins containing a heme, with a central Fe atom at its core, as a cofactor. They are involved in electron transport chain and redox catalysis. They are classified according to the type of heme and its mode of bin ...
to
cytochrome oxidase
The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes.
It is the last enzyme in the respiratory el ...
.
Predicted functional partners include coxD (cytochrome c oxidase, aa3-type, subunit IV, 64
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
s),
coxC (cytochrome c oxidase, aa3-type, subunit III, 184
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
s),
ctaB (protoheme IX
farnesyltransferase
Farnesyltransferase () is one of the three enzymes in the prenyltransferase group. Farnesyltransferase (FTase) adds a 15-carbon isoprenoid called a farnesyl group to proteins bearing a CaaX motif: a four-amino acid sequence at the carboxyl te ...
),
Cyc2 (cytochrome c, 485
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
s), AFE_3142 (major facilitator family transporter, 397
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
s),
coxA (cytochrome c oxidase, aa3-type, subunit I, 627
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
s),
Cyc1 (cytochrome c552, 230
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
s), and AFE_3141 (rrf2 family protein, 146
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
s).
Reactions
Fe(II) redox of cytochrome c552 and rusticyanin occurs with the following:
Fe
2+ embrane/sub> + an oxidized rusticyanin embrane/sub> → Fe3+ embrane/sub> + a reduced rusticyanin embrane/sub>;
a reduced rusticyanin embrane/sub> + an oxidized cytochrome c552 embrane/sub> → an oxidized rusticyanin embrane/sub> + a reduced cytochrome c552 embrane/sub>;
a reduced rusticyanin utside cell/sub> + an oxidized CycA1 cytochrome utside cell/sub> → a reduced CycA1 cytochrome utside cell/sub> + an oxidized rusticyanin utside cell/sub>
References
{{Reflist
Copper proteins