Cloning and characterization of a novel sigma-like glutathione S-transferase from the giant panda parasitic nematode, Baylisascaris schroederi

Background: Baylisascaris schroederi, an intestinal nematode of the giant panda, is the cause of the often fatal disease, baylisascariasis. Glutathione S-transferases (GSTs) are versatile enzymes that can affect parasite survival and parasite-host interactions and, are therefore, potential targets for the development of diagnostic tests and vaccines. Methods: In this study, we identified a full-length cDNA that encoded a novel, secretory sigma-like GST (Bsc-GST sigma) from a B. schroederi-omic dataset. Following cloning and sequencing, sequence and structural analyses and comparative modeling were performed using online-bioinformatics and proteomics tools. The recombinant Bsc-GSTs (rBsc-GST sigma) protein was prokaryotically expressed and then used to detect antigenicity and reactivity using immunoblotting assays. In addition, the native protein in female adult B. schroederi was located via immunofluorescence techniques, while the preliminary ELISA-based serodiagnostic potential of rBsc-GSTs was assessed in native and infected mouse sera. Results: Bsc-GSTs contained a 621-bp open reading frame that encoded a polypeptide of 206 amino acids with two typical sigma GST domain profiles, including a GST_N_Sigma_like at the N-terminus and a GST_C_Sigma_like at the C-terminus. The presence of an N-terminal signal sequence indicated that Bsc-GSTs was a secretory protein. Sequence alignment and phylogenetic analyses showed that Bsc-GSTs was a nematode-specific member of the Sigma class GSTs and shared the closest genetic distance with its homologue in Ascaris suum. Further comparative structure analyses indicated that Bsc-GSTs possessed the essential structural motifs (e.g., beta alpha beta alpha beta beta alpha) and the consensus secondary or tertiary structure that is typical for other characterized GST sigma s. Immunolocalization revealed strong distributions of native Bsc-GSTs in the body hypodermis, lateral chords, gut epithelium, gut microvilli, oviduct epithelium, and ovaries of adult female worms, similar to its homologue in A. suum. Building on good immunogenic properties, rBsc-GST sigma-based ELISA exhibited a sensitivity of 79.1% and a specificity of 82.0% to detect anti-B. schroederi IgG antibodies in the sera of experimentally infected mice. Conclusion: This study presents a comprehensive demonstration of sequence and structural-based analysis of a new, secretory sigma-like GST from a nematode, and its good serodiagnostic performance suggests that rBsc-GSTs has the potential to detect B. schroederi and, therefore, could be used to develop an ELISA-based serological test to diagnose baylisascariasis in giant pandas.