title: Pattern of nucleotide substitution and divergence of prophenoloxidase in decapods.
abstract: Despite the unprecedented development in identification and characterization of prophenoloxidase (proPO) in commercially important decapods, little is known about the evolutionary relationship, rate of amino acid replacement and differential selection pressures operating on proPO of different species of decapods. Here we report the evolutionary relationship among these nine decapod species based on proPO gene and types of selective pressures operating on proPO codon sites. Our analyses revealed that all the nine decapod species shared a common ancestor. The mean percentage sequence divergence at proPO gene was 34.4+/-0.6%. Pairwise estimates of nonsynonymous to synonymous ratio (omega) for Homarus americanus-H. gammarus is greater than one, therefore indicating adaptive evolution (functional diversification) of proPO in these two species. In contrast, strong purifying selection (omega<1) was observed in all other species pairs. However, phylogenetically closely related decapods revealed relatively higher omega value (omega=0.15+/-0.3) than the distantly related species pairs (omega=0.0075+/-0.005). These discrepancies could be due to higher fixation probability of beneficial mutation in closely related species. Maximum likelihood-based codon substitution analyses revealed a strong purifying selection operating on most of the codon sites, therefore suggesting proPO is functionally constrained (purifying selection). Codon substitution analyses have also revealed the evidence of strong purifying selection in haemocyanin subunits of decapods.
authors.affiliation: Department of Biological Science, University of Tulsa, 600 South College Avenue, Tulsa, OK 74104, USA. abinash-padhi@utulsa.edu
authors.forename: Abinash
authors.initials: A
authors.lastname: Padhi
authors.forename: Bindhu
authors.initials: B
authors.lastname: Verghese
authors.forename: Ajula
authors.initials: A
authors.lastname: Vaid
authors.forename: Subhendu K
authors.initials: SK
authors.lastname: Otta
mesh_terms: D000818:Animals; D004156:Catechol Oxidase / Q000235:genetics*; D033364:Decapoda / Q000201:enzymology* / Q000235:genetics*; D004792:Enzyme Precursors / Q000235:genetics*; D014644:Genetic Variation; D006433:Hemocyanins / Q000235:genetics; D010802:Phylogeny; D017354:Point Mutation / Q000235:genetics*; D017422:Sequence Analysis, DNA / Q000662:veterinary; D020539:Sequence Analysis, Protein / Q000662:veterinary; D012689:Sequence Homology, Nucleic Acid
chemical_list: D004792:Enzyme Precursors; D006433:Hemocyanins; C038451:pro-phenoloxidase; D004156:Catechol Oxidase