Cryptocyanin, a crustacean molting protein: Evolutionary link with arthropod hemocyanins and insect hexamerins
- *Oregon Institute of Marine Biology, University of Oregon, Charleston, OR 97420 and Department of Biology, University of Oregon, Eugene, OR 97403; and ‡Department of Chemistry, Texas A&M University, College Station, TX 77801
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Edited by K. E. van Holde, Oregon State University, Corvallis, OR, and approved December 10, 1998 (received for review September 14, 1998)
Abstract
Cryptocyanin, a copper-free hexameric protein in crab (Cancer magister) hemolymph, has been characterized and the amino acid sequence has been deduced from its cDNA. It is markedly similar in sequence, size, and structure to hemocyanin, the copper-containing oxygen-transport protein found in many arthropods. Cryptocyanin does not bind oxygen, however, and lacks three of the six highly conserved copper-binding histidine residues of hemocyanin. Cryptocyanin has no phenoloxidase activity, although a phenoloxidase is present in the hemolymph. The concentration of cryptocyanin in the hemolymph is closely coordinated with the molt cycle and reaches levels higher than hemocyanin during premolt. Cryptocyanin resembles insect hexamerins in the lack of copper, molt cycle patterns of biosynthesis, and potential contributions to the new exoskeleton. Phylogenetic analysis of sequence similarities between cryptocyanin and other members of the hemocyanin gene family shows that cryptocyanin is closely associated with crustacean hemocyanins and suggests that cryptocyanin arose as a result of a hemocyanin gene duplication. The presence of both hemocyanin and cryptocyanin in one animal provides an example of how insect hexamerins might have evolved from hemocyanin. Our results suggest that multiple members of the hemocyanin gene family—hemocyanin, cryptocyanin, phenoloxidase, and hexamerins—may participate in two vital functions of molting animals, oxygen binding and molting. Cryptocyanin may provide important molecular data to further investigate evolutionary relationships among all molting animals.
Footnotes
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↵ † To whom reprint requests should be addressed at: Oregon Institute of Marine Biology, Boat Basin Drive, Charleston, OR 97420. e-mail: nterwill{at}oimb.uoregon.edu.
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This paper was submitted directly (Track II) to the Proceedings Office.
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Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. AF091261).
- ABBREVIATIONS:
- CuA and CuB,
- copper binding sites in arthropod hemocyanins
- Copyright © 1999, The National Academy of Sciences
