Structure of arthropodan hemocyanin.

The X-ray structure of spiny lobster deoxy-hemocyanin has been determined at 3.2 A resolution. This oxygen-carrying type III copper protein is a hexamer with a molecular weight of approximately 460,000. Each subunit is folded into three domains, of which the structure is qualitatively described. The oxygen binding dinuclear copper site is located in the second domain. Each copper is surrounded by three histidines. An analysis of inter subunit contacts shows that the hemocyanin hexamer is best described as a trimer of dimers. Available amino acid sequence and electron microscopy data suggest that the polypeptide architecture of spiny lobster hemocyanin is common to all arthropodan hemocyanins.