InterPro domain: IPR035938

The hemerythrin family is composed of hemerythrin proteins found in invertebrates, and a broader collection of bacterial and archaeal homologues. Hemerythrin is an oxygen-binding protein found in the vascular system and coelomic fluid, or in muscles (myohemerythrin) in invertebrates [ 1 ]. Many of the homologous proteins found in prokaryotes are multi-domain proteins with signal-transducing domains such as the GGDEF diguanylate cyclase domain ( IPR000160 ) and methyl-accepting chemotaxis protein (MCP) signalling domain ( IPR004089 ). Most hemerythrins are oxygen-carriers with a bound non-haem iron, but at least one example is a cadmium-binding protein, apparently with a role in sequestering toxic metals rather than in binding oxygen. The prokaryote with the most instances of this domain is Magnetococcus sp. MC-1, a magnetotactic bacterium.

Hemerythrins and myohemerythrins [ 2 , 3 ] are small proteins of about 110 to 129 amino acid residues that bind two iron atoms. They are left-twisted 4-alpha-helical bundles, which provide a hydrophobic pocket where dioxygen binds as a peroxo species, interacting with adjacent aliphatic side chains via van der Waals forces [ 4 ]. In both hemerythrins and myohemerythrins, the active centre is a binuclear iron complex, bound directly to the protein via 7 amino acid side chains [ 5 ], 5 His, 1 Glu and 1 Asp [ 5 ]. Ovohemerythrin [ 5 ], a yolk protein from the leech Theromyzon tessulatum seems to belong to this family of proteins, it may play a role in the detoxification of free iron after a blood meal [ 6 ].

1. Primary structure of myohemerythrin from the annelid Nereis diversicolor. FEBS Lett. 285, 25-7
2. Structure of myohemerythrin in the azidomet state at 1.7/1.3 A resolution. J. Mol. Biol. 197, 273-96
3. The amino acid sequence of hemerythrin from Siphonosoma cumanense. Protein Seq. Data Anal. 3, 141-7
4. Active site structures of deoxyhemerythrin and oxyhemerythrin. Proc. Natl. Acad. Sci. U.S.A. 82, 713-6
5. Ovohemerythrin, a major 14-kDa yolk protein distinct from vitellogenin in leech. Eur. J. Biochem. 209, 563-9