Studies of a novel hemerythrin-like protein from the anaerobic, hyperthermophilic archaeon, methanococcus jannaschii

Hemerythrin (Hr) is a non-heme iron protein, which originally had only been found in marine invertebrates where it functions as an oxygen-transport or storage protein. Hrs typically contain an oxo-/hydroxo-bridged non-heme diiron site surrounded by a four-helical bundle protein fold. All Hrs have seven conserved amino acids that furnish iron ligands, namely five histidines, one aspartate and one glutamate. Subsequently, homologues have been found in other organisms. Through protein and nucleotide searches, a previously undescribed protein having the Hr-like sequence motif (MjHr), was discovered in the Methanococcus jannaschii genome. MjHr exhibits structural and spectral properties resembling those of previously characterized Hrs. This Hr-like protein is the first to be described from archaea. Unlike Hrs that function as O2- carrying proteins, MjHr is proposed to function as an O2 sensor or scavenger within this methanogenic anaerobe.