Hemerythrin
Hemerythrin-like family | |||||||||
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Hemerythrin (also spelled haemerythrin;
Hemerythrin does not, as the name might suggest, contain a heme. The names of the blood oxygen transporters hemoglobin, hemocyanin, and hemerythrin do not refer to the heme group (only found in globins). Instead, these names are derived from the Greek word for blood. Hemerythrin may also contribute to innate immunity and anterior tissue regeneration in certain worms.[1]
O2 binding mechanism
The mechanism of dioxygen binding is unusual. Most O2 carriers operate via formation of
Fe2+—OH—Fe2+ | deoxy (reduced) |
Fe2+—OH—Fe3+ | semi-met |
Fe3+—O—Fe3+—OOH− | oxy (oxidized) |
Fe3+—OH—Fe3+— (any other ligand) | met (oxidized) |
The uptake of O2 by hemerythrin is accompanied by two-electron oxidation of the diferrous centre to produce a hydroperoxide (OOH−) complex. The binding of O2 is roughly described in this diagram:
Deoxyhemerythrin contains two high-spin ferrous ions bridged by
Quaternary structure and cooperativity
Hemerythrin typically exists as a homooctamer or heterooctamer composed of α- and β-type subunits of 13–14 kDa each, although some species have dimeric, trimeric and tetrameric hemerythrins. Each subunit has a four-α-helix fold binding a binuclear iron centre. Because of its size hemerythrin is usually found in cells or "corpuscles" in the blood rather than free floating.
Unlike hemoglobin, most hemerythrins lack
Hemerythrin affinity for carbon monoxide (CO) is actually lower than its affinity for O2, unlike hemoglobin which has a very high affinity for CO. Hemerythrin's low affinity for CO poisoning reflects the role of hydrogen-bonding in the binding of O2, a pathway mode that is incompatible with CO complexes which usually do not engage in hydrogen bonding.
Hemerythrin/HHE cation-binding domain
The hemerythrin/HHE cation-binding
Hemerythrin/HHE (H-HxxxE-HxxxH-HxxxxD) proteins found in bacteria are implicated in signal transduction and chemotaxis. More distantly related ones include H-HxxxE-H-HxxxE proteins (including the
References
Further reading
- Karlsen, O.A., Ramsevik, L., Bruseth, L.J., Larsen, Ø., Brenner, A., Berven, F.S., Jensen, H.B. and Lillehaug, J.R. (2005). "Characterization of a prokaryotic haemerythrin from the methanotrophic bacterium Methylococcus capsulatus (Bath)". FEBS J. 272 (10): 2428–2440. S2CID 11002682.)
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: CS1 maint: multiple names: authors list (link - Stenkamp, R.E. (1994). "Dioxygen and hemerythrin". Chem. Rev. 94 (3): 715–726. .