title: Evolution of the arthropod prophenoloxidase/hexamerin protein family.
abstract: Phylogenetic analysis of the prophenoloxidase/hexamerin family of arthropods revealed four well supported subfamilies: (1) the arylphorin subfamily, including arylphorins, storage proteins, and other proteins of uncertain function from insects; (2) the hemocyanins of branchiopod crustaceans, which are copper-binding proteins involved in oxygen transport; (3) the hemocyanins of chelicerates; and (4) the prophenoloxidases (proPO) of both insects and branchiopods, which are copper-binding molecules that play a role in sclerotization of cuticle and encapsulation of foreign particles. The phylogeny indicated that insect and branchiopod proPO constitute a monophyletic group but that branchiopod and chelicerate hemocyanins do not constitute a monophyletic group. Branchiopod hemocyanin and proPO diverged from each other prior to the divergence of insects from branchiopods and probably prior to the divergence of chelicerates from the insect-branchiopod lineage. Likewise, the insect arylphorin subfamily diverged from proPO prior to the divergence of insects from branchiopods and probably prior to the divergence of chelicerates; thus, the results did not support the hypothesis that insect arylphorins represent hemocyanins freed to assume a new function because the insect tracheal respiratory system removes the need for an oxygen-transport molecule. Nonetheless, reconstruction of ancestral sequences by the maximum parsimony method suggested that the ancestors of the arylphorin family were copper-binding. Regions corresponding to the copper-binding domains were found to have a faster rate of nonsynonymous evolution in arylphorin subfamily genes than in other hexamerin family genes; this presumably reflects a relaxation of purifying selection after the loss of copper-binding function.
authors.affiliation: Department of Biology, Institute of Molecular Evolutionary Genetics, The Pennsylvania State University, University Park 16803, USA. austin@hugans3.bio.psu.edu
authors.forename: A L
authors.initials: AL
authors.lastname: Hughes
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001181:Arthropods / Q000201:enzymology / Q000235:genetics*; D004156:Catechol Oxidase / Q000737:chemistry* / Q000235:genetics*; D004792:Enzyme Precursors / Q000737:chemistry* / Q000235:genetics*; D019143:Evolution, Molecular; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics; D006433:Hemocyanins / Q000737:chemistry / Q000235:genetics; D019476:Insect Proteins / Q000737:chemistry* / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D011336:Probability; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D004792:Enzyme Precursors; D006023:Glycoproteins; D019476:Insect Proteins; C041137:storage proteins, Insecta; D006433:Hemocyanins; C038451:pro-phenoloxidase; D004156:Catechol Oxidase