Isolation and characterization of the cDNA encoding the prophenoloxidase of fall webworm, hyphantria cunea

Two kinds of cDNA clones encoding prophenoloxidases (ProPO; zymogen of phenoloxidase (monophenol, L-dopa: oxygen oxydoreductase, EC 1.14.18.1)) were isolated by polymerase chain reaction (PCR) followed by screening of cDNA library that was prepared from whole larvae of the fall webworm, Hyphantria cunea (Lepidoptera, Arctiidae). The cDNAs encode 681 and 697 amino acids with molecular masses of 78.2 and 80.2 kDa, respectively. Deduced amino acid sequence homology between the two H. cunea ProPOs are only 49% whereas the homology against other insect ProPOs ranged from about 40 to 72%. The phylogenic analysis showed that the insect ProPOs are grouped mainly into two families. A putative proteolytic cleavage site for enzyme activation was identical to other insect ProPOs. The conserved copper binding sites were 84-62% homologous to arthropod ProPOs. Two additional highly conserved regions were found in the carboxy terminal. Furthermore, like other insect prophenoloxidases, hydrophobic signal peptide sequences were absent in the deduced ProPOs from H. cunea. Southern blot analysis indicated that the H. cunea ProPO1 is present as a single copy in the genome. Northern blot analysis showed that the expression of the ProPO genes were concentrated in mid-instar larvae, but were much lower in other developmental stages.