Chitinase genes expressed by infective larvae of the filarial nematodes, Acanthocheilonema viteae and Onchocerca volvulus

Stage-specific products of 220 and 75 kDa were identified by metabolic labelling of infective larvae of the filarial nematode Acanthocheilonema viteae in ticks. Synthesis was temperature sensitive, occuring at 27°C but not at 37°C. These products were secreted 3–6 days after leaving the vector during post-infective development, but subsequent expression was not detected. The smaller protein with a p I of 6.2, was purified by two-dimensional electrophoresis and the N-terminal amino acid sequence was derived. This provisionally identified the protein as a chitinase, which was confirmed biochemically by glycol-chitin substrate gel electrophoresis. The polymerase chain reaction was used to amplify a product from a cDNA library of A. viteae infective larvae. The nucleotide sequence codes for a putative signal peptide of 20 amino acids and a mature protein of 504 residues ( M r 56 kDa), exhibiting 69% identity (81% similarity allowing for conservative substitutions) with the MFI chitinase described from microfilariae of Brugia malayi [21]. N-linked glycosylation may account for some, or all, of the discrepancy in M r between the predicted polypeptide and the native parasite product (75 kDa). Primers based on the A. viteae sequence were used to amplify a related sequence from a cDNA library of Onchocerca volvulus infective larvae. The O. volvulus cDNA codes for a 20-amino acid signal peptide followed by 477 residues with an M r of 54 kDa, and shares 67% identity with the A. viteae chitinase (80% similarity allowing for conservative substitutions) and 69% identity with the B. malayi MF1 molecule. It is proposed that chitinases expressed by infective stages of these filarial nematodes may play a role in ecdysis during post-infective development.