Identification of the major soluble cuticular glycoprotein of lymphatic filarial nematode parasites (gp29) as a secretory homolog of glutathione peroxidase.

Abstract

Lymphatic filariasis is a serious debilitating disease that affects some 90 million people worldwide (1). The causative agents, filarial nematodes of the genera Brugia and Wuchereria, are parasites that persist for long periods of time in the human lymphatic system. They achieve this longevity despite a vigorous host immune response and their apparent inability to undergo antigenic variation, implying a sustained resistance to or subversion of host immunity. All nematodes are bounded by a cuticle, an extracellular matrix composed predominantly of collagens, and a highly cross-linked external envelope of proteins termed cuticlin (2, 3). In contrast to these conserved structural elements, the nematode cuticle exhibits an extremely restricted profile of soluble constituent proteins that may be species-or stagespecific (3, 4). The major protein of adult lymphatic filarial parasites defined by surface labeling is a 29-kDa glycoprotein (gp29) that appears to be expressed after infection of the mammalian host (5-11). Peptide mapping has shown that gp29 from Brugia pahangi and Brugia malayi are highly homologous (8), and the 29-kDa surface-labeled protein from Brugia timori (5) and Wuchereria bancrofti (6) probably represents the same molecule. In adult B. malayi gp29 is synthesized in the syncytial hypodermis, exported to the cuticle, and released into the external environment during in vitro culture (9, 10).We report here the isolation and sequence of cDNAs that encode gp29 from B. pahangi,t which reveals that this cuticular protein is a homolog of the antioxidant enzyme glutathione peroxidase (GSHPx). A possible biological role for this enzyme in defense against immune-mediated cytotoxicity is discussed. MATERIALS AND METHODSParasites. B. malayi were obtained from TRS laboratories, Athens, GA. Adult worms were recovered from the peritoneal cavities ofjirds (Meriones unguiculatus) infected over 3 mo previously with 200 infective larvae and washed extensively with phosphate-buffered saline.Labeling Procedures and Immunochemical Analysis. Adult B. malayi (mixed sex) were extrinsically labeled with BoltonHunter reagent and Iodo-Gen as described elsewhere (12). Parasites were also metabolically labeled with sodium[5S]selenite at 0.25 mCi ml-1 (Amersham SCS-1; 1 Ci = 37 GBq) via in vitro culture for 24 hr in RPMI 1640 medium/2 mM glutamine/1% glucose/penicillin at 100 units-ml-'/ streptomycin at 100 ,ugml-1. All labeled preparations were homogenized in phosphate-buffered saline/1.5% 1-octyl glucoside containing a mixture of protease inhibitors (12) and then centrifuged at 11,000 x g. Immunoprecipitation assays were done with 2.5 ,ul of antiserum in a total volume of 50 ,ul as described (12), resolved on 7-25% gradient polyacrylamide gels, and autoradiographed.cDNA Isolation, Confirmation, and Sequence Determination. A cDNA library in bacteriophage Agtll constructed from mRNA of mixed adult B. pahangi (13) was screened with a polyclonal antiserum to gp29 (9). Clones that reacted positively against gp29 in immunoprecipitatio...

Putative phospholipid hydroperoxide glutathione peroxidase gene from Arabidopsis thaliana induced by oxidative stress.

“…The deduced amino acid sequence showed 42% homology with human liver SeCys-dependent glutathione peroxidase and SeCys in the active site was substituted by Cys (Cookson et al, 1992). The enzyme has activity toward phospholipid hydroperoxide and linolenic acid hydroperoxide but no significant activity toward hydrogen peroxide, whereas mammalian SeCys-dependent glutathione peroxidase has activity toward hydrogen peroxide and linolenic acid hydroperoxide but not toward phospholipid hydroperoxide (Tang et al, 1995).…”

The thioredoxin system of Plasmodium falciparum and other parasites

“…A therapeutic and prophylactic potential of targeting the Trx system can be deduced from the fact that immunization with TPx has conferred protective immune responses against L. major [143] and E. histolytica [148], and that selective disruption of the TPx gene in Saccharomyces cerevisae resulted in a mutant strain with enhanced sensitivity to oxidative stress [149]. Furthermore, helminthic parasites are likely to adapt to oxidative stress by synthesizing high levels of antioxidant enzymes and by expressing them at the hostparasite interface [77,150,151]. The most promising intervention targets are obviously the parasitic TrxRs because they differ from the human isofunctional enzymes.…”

A Selenoprotein in the Plant Kingdom

“…A gene encoding a putative GPX containing selenocysteine was found in the parasitic helminth Schistosoma mansoni (11), but GPX-like genes that carry the code for a catalytic Cys residue, not Sec, were isolated from the nematode Burgia pahangi (12), Neisseria meningitidis (13), and the malaria parasite Plasmodium falciparum (14). DNA sequences that could potentially code for selenoproteins have been found in viruses as well (15).…”