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Characterization of a prokaryotic haemerythrin from the methanotrophic bacterium Methylococcus capsulatus (Bath)
Author(s) -
Karlsen Odd A.,
Ramsevik Linda,
Bruseth Live J.,
Larsen Øivind,
Brenner Annette,
Berven Frode S.,
Jensen Harald B.,
Lillehaug Johan R.
Publication year - 2005
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2005.04663.x
Subject(s) - subfamily , rhodobacter , biochemistry , biology , escherichia coli , peptide sequence , amino acid , sequence alignment , bacteria , fusion protein , gene , recombinant dna , chemistry , genetics , mutant
For a long time, the haemerythrin family of proteins was considered to be restricted to only a few phyla of marine invertebrates. When analysing differential protein expression in the methane‐oxidizing bacterium, Methylococcus capsulatus (Bath), grown at a high and low copper‐to‐biomass ratio, respectively, we identified a putative prokaryotic haemerythrin expressed in high‐copper cultures. Haemerythrins are recognized by a conserved sequence motif that provides five histidines and two carboxylate ligands which coordinate two iron atoms. The diiron site is located in a hydrophobic pocket and is capable of binding O 2 . We cloned the M. capsulatus haemerythrin gene and expressed it in Escherichia coli as a fusion protein with NusA. The haemerythrin protein was purified to homogeneity cleaved from its fusion partner. Recombinant M. capsulatus haemerythrin (McHr) was found to fold into a stable protein. Sequence similarity analysis identified all the candidate residues involved in the binding of diiron (His22, His58, Glu62, His77, His81, His117, Asp122) and the amino acids forming the hydrophobic pocket in which O 2 may bind (Ile25, Phe59, Trp113, Leu114, Ile118). We were also able to model a three‐dimensional structure of McHr maintaining the correct positioning of these residues. Furthermore, UV/vis spectrophotometric analysis demonstrated the presence of conjugated diiron atoms in McHr. A comprehensive genomic database search revealed 21 different prokaryotes containing the haemerythrin signature (PROSITE 00550), indicating that these putative haemerythrins may be a conserved prokaryotic subfamily.