Characterization of a novel glycosylated glutathione transferase of Onchocerca ochengi, closest relative of the human river blindness parasite.

Clair Rose,E James La Course,Jem Davis,Stuart D Armstrong,Aitor Casas-Sanchez,Giorgio Praulins,Gemma Molyneux,Samirah Perally,Benjamin L Makepeace,Anne Rutter,Mark Prescott,Zenaida Stead,Cristina Yunta,Alvaro Acosta-Serrano

doi:10.1017/s0031182019000763

Clair Rose, E James La Course + Show 12 more

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https://doi.org/10.1017/s0031182019000763

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Abstract

Filarial nematodes possess glutathione transferases (GSTs), ubiquitous enzymes with the potential to detoxify xenobiotic and endogenous substrates, and modulate the host immune system, which may aid worm infection establishment, maintenance and survival in the host. Here we have identified and characterized a σ class glycosylated GST (OoGST1), from the cattle-infective filarial nematode Onchocerca ochengi, which is homologous (99% amino acid identity) with an immunodominant GST and potential vaccine candidate from the human parasite, O. volvulus, (OvGST1b). Onchocerca ochengi native GSTs were purified using a two-step affinity chromatography approach, resolved by 2D and 1D SDS-PAGE and subjected to enzymic deglycosylation revealing the existence of at least four glycoforms. A combination of lectin-blotting and mass spectrometry (MS) analyses of the released N-glycans indicated that OoGST1 contained mainly oligomannose Man5GlcNAc2 structure, but also hybrid- and larger oligommanose-type glycans in a lower proportion. Furthermore, purified OoGST1 showed prostaglandin synthase activity as confirmed by Liquid Chromatography (LC)/MS following a coupled-enzyme assay. This is only the second reported and characterized glycosylated GST and our study highlights its potential role in host-parasite interactions and use in the study of human onchocerciasis.

Highlights

The cattle filarial nematode Onchocerca ochengi is a well-established model natural system for the study of human onchocerciasis, the causative agent of which is O. volvulus (Trees, 1992; Makepeace and Tanya, 2016)
All three nematode GSTs are σ class, have a 25-amino acid signal peptide that is cleaved prior to maturation and possess a 25-amino acid N-terminal extension not found in any other GST to date
The σ class GST of O. ochengi is of particular interest in terms of the potential involvement in host immune modulation as well as possible roles in detoxification of other endogenous host- and parasite- derived toxins

Summary

Introduction

The cattle filarial nematode Onchocerca ochengi is a well-established model natural system for the study of human onchocerciasis, the causative agent of which is O. volvulus (Trees, 1992; Makepeace and Tanya, 2016). In efforts to discover new ways to control onchocerciasis, much research has been focused on the molecules which may allow Onchocerca spp. to establish and maintain infection One such protein family is the glutathione transferases (GSTs) which may aid worm survival through detoxification of drugs and evasion of host-derived immunochemical attack, and with the potential to play roles in immunomodulation (Chasseaud, 1979; Jakoby and Habig, 1980; Brophy and Barrett, 1990; Sheehan et al, 2001; Sommer et al, 2003; Hayes et al, 2005). Whilst most screening of parasite products for immunoreactive vaccine candidate antigens is predominantly protein focused (Diemert et al, 2018), antibody responses to glycosylated proteins demonstrates the high immunogenicity of glycan extensions, highlighting the clear rationale for a greater attention (Jaurigue and Seeberger, 2017)

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