Rubrerythrin (RBR) is a non-

heme Heme (American English), or haem (Commonwealth English, both pronounced /Help:IPA/English, hi:m/ ), is a ring-shaped iron-containing molecule that commonly serves as a Ligand (biochemistry), ligand of various proteins, more notably as a Prostheti ...

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

-containing

metalloprotein 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 (out of ~20,000) contain zinc-binding protein domains al ...

involved in

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...

tolerance within

anaerobic bacteria An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenat ...

. It contains a di-iron active site, where

peroxide In chemistry, peroxides are a group of Chemical compound, compounds with the structure , where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical) and O's are single oxygen atoms. Oxygen atoms are joined ...

is reduced into two water molecules, and a mono-iron

rubredoxin Rubredoxins are a class of low-molecular-weight iron-containing proteins found in sulfur-metabolizing bacteria and archaea. Sometimes rubredoxins are classified as iron-sulfur proteins; however, in contrast to iron-sulfur proteins, rubredoxins ...

-like domain thought to be involved in

electron transfer Electron transfer (ET) occurs when an electron relocates from an atom, ion, or molecule, to another such chemical entity. ET describes the mechanism by which electrons are transferred in redox reactions. Electrochemical processes are ET reactio ...

. A majority of known RBR families are utilized as peroxide "scavengers" to defend organisms against oxidative stress.

Function

As a member of the

Ferritin Ferritin is a universal intracellular and extracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including archaea, bacteria, algae, higher plants, and animals. ...

-like superfamily, RBRs primary function is iron storage and detoxification. Rubrerythrins utilize their di-iron centers to bind with

reactive oxygen species In chemistry and biology, reactive oxygen species (ROS) are highly Reactivity (chemistry), reactive chemicals formed from diatomic oxygen (), water, and hydrogen peroxide. Some prominent ROS are hydroperoxide (H2O2), superoxide (O2−), hydroxyl ...

such as

Hydrogen Peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

, further reducing them into

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

. RBR reduction is theorized as a particularly important adaptation that occurred in response to the

Great Oxygenation event The Great Oxidation Event (GOE) or Great Oxygenation Event, also called the Oxygen Catastrophe, Oxygen Revolution, Oxygen Crisis or Oxygen Holocaust, was a time interval during the Earth's Paleoproterozoic era when the Earth's atmosphere and ...

, increasing defensive fitness of all cells exposed to relatively high levels of oxygen and similar byproducts. Although primarily studied within anaerobic bacteria, RBRs have been discovered in multiple different types of cells including: Aerobic, Anaerobic, and

Cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

Structure

Many formations of RBRs can be identified by four helical structures, chains alpha and beta containing 3

atoms. Both N and C-terminals of common RBRs are very similar to Rubredoxin containing amino acid residue sequences. Furthermore, both metalloproteins contain 5

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an Amine, α-amino group (which is in the protonated –NH3+ form under Physiological condition, biological conditions), a carboxylic ...

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s located within the N-terminals of their peptide chains.

Mechanism

In a reduced state without exposure to reactive oxygen byproducts, Rubrerythrin contains two water molecules near its di-iron center. During and after exposure to peroxide, Rubrerythrin becomes oxidized, changing rotational conformations beginning around the peroxide binding site.

References

Iron–sulfur proteins Metalloproteins Bacterial proteins {{protein-stub