Hemocyanin/hexamerin middle domain (IPR000896)

Short name: Hemocyanin/hexamerin_mid_dom

Overlapping homologous superfamilies

Domain relationships



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.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.