Pathways & interactions
Hemocyanin/hexamerin middle domain (IPR000896)
Short name: Hemocyanin/hexamerin_mid_dom
Overlapping homologous superfamilies
- Uncharacterised domain, di-copper centre (IPR008922)
Crustacean and cheliceratan hemocyanins (oxygen-transport proteins) and insect hexamerins (storage proteins) are homologous gene products, although the latter do not bind oxygen [PMID: 8015442].
Haemocyanins are found in the haemolymph of many invertebrates. They are divided into 2 main groups, arthropodan and molluscan. These have structurally similar oxygen-binding centres, which are similar to the oxygen-binding centre of tyrosinases, but their quaternary structures are arranged differently. The arthropodan proteins exist as hexamers comprising 3 heterogeneous subunits (a, b and c) and possess 1 oxygen-binding centre per subunit; and the molluscan proteins exist as cylindrical oligomers of 10 to 20 subunits and possess 7 or 8 oxygen-binding centres per subunit [PMID: 3207675]. Although the proteins have similar amino acid compositions, the only real similarity in their primary sequences is in the region corresponding to the second copper-binding domain, which also shows similarity to the copper-binding domain of tyrosinases.
Hexamerins are proteins from the hemolymph of insects, which may serve as a store of amino acids for synthesis of adult proteins. They do not possess the copper-binding histidines present in hemocyanins [PMID: 8015442].
Homologues are also present in other kinds of organism, for example, AsqI from the yeast Emericella nidulans. This is a tyrosinase involved in biosynthesis of the aspoquinolone mycotoxins, though its exact function is unknown [PMID: 25251934].
This entry represents the middle domain of hemocyanin and hexamerin proteins, which is involved in copper binding in hemocyanins.
- PF00372 (Hemocyanin_M)