Cloning and Sequence Analysis of Prophenoloxidase from Haemocytes of the Red Swamp Crayfish, Procambarus clarkii

The full-length cDNA sequence of prophenoloxidase was obtained through RACE technology. The complete cDNA sequence is 3 721-bp long, containing an open reading frame (ORF) of 1 881 bp, a 154-bp 5'-untranslated region, and a 1 686-bp 3'-untranslated region with three potential functional poly(A) signals (AATAAA). The molecular mass of the deduced amino acid sequence (627 aa) was 72.3 kDa with an estimated pI of 5.88. It contained putative copper-binding sites (copper A: 131, 135, 167 and copper B: 301, 305, 341), and a tentative complement-like motif (GCGWPDHL). Eight potential N-linked glycosylation sites were predicted to be present in P. clarkii prophenoloxidase. Similar to those in other arthropod prophenoloxidases reported so far, no signal peptide was detected in the crayfish prophenoloxidase. The phylogenetic trees confirmed that P. clarkii prophenoloxidase was most closely related to that of freshwater crayfish P. leniusculus and more closely related to other crustacean prophenoloxidases from shrimp, prawn, and lobster than to the insect prophenoloxidases. Besides, two putative introns were found in this sequence of genomic DNA.