Identification of an asparagine amidohydrolase from the filarial parasite Dirofilaria immitis

The nematode cuticle is a complex extracellular structure which is secreted by an underlying syncytium of hypodermal cells. Recent studies have demons trated that the cuticle of parasitic nematodes is a dynamic structure with important absorptive, secretory, and enzymatic activities. In addition, the cuticle serves as a protective barrier against the host. A 48-h third stag e larval Dirofilaria immitis cDNA library was immunoscreened with sera rais ed against larval cuticles. One clone, L3MC4 that reacted strongly with the anti-cuticle antisera was sequenced. The composite cDNA sequence comprises 2073 bp coding for a full-length protein of 590 amino acids. GenBank analy sis showed that DiAsp had significant similarity to a Caenorhabditis elegan s gene-product (54% identity) and to other asparaginases at the amino acid level. Escherichia coli-expressed recombinant DiAsp (rDiAsp) catalysed the hydrolysis of asparagine to aspartate and ammonia. Antibodies raised agains t D. immitis larval cuticles reacted with rDiAsp in immunoblots. This is th e first report of identification of a cDNA clone encoding an asparaginase e nzyme from a parasitic nematode. (C) 1999 Australian Society for Parasitolo gy Inc. Published by Elsevier Science Ltd. All rights reserved.