The secretory omega‐class glutathione transferase OvGST3 from the human pathogenic parasite Onchocerca volvulus

Abstract

The glutathione S-transferases (GSTs) constitute a highly versatile superfamily that is thought to have evolved from a thioredoxin-like ancestor in response to the development of oxidative stress, sharing sequence and structural similarities with several stress-related proteins in a widespread range of organisms. Additionally, several GST-related proteins have been described, demonstrating that this ancient protein fold has been 'recycled' by nature for new functions, such as plant stress-induced proteins, bacterial stringent starvation Onchocerciasis or river blindness, caused by the filarial nematode Onchocerca volvulus, is the second leading cause of blindness due to infectious diseases. The protective role of the omega-class glutathione transferase 3 from O. volvulus (OvGST3) against intracellular and environmental reactive oxygen species has been described previously. In the present study, we continue our investigation of the highly stress-responsive OvGST3. Alternative splicing of two exons and one intron retention generates five different transcript isoforms that possess a spliced leader at their 5¢-end, indicating that the mechanism of mature mRNA production involves alternative-, cis-and trans-splicing processes. Interestingly, the first two exons of the ovgst3 gene encode a signal peptide before sequence identity to other omega-class glutathione transferases begins. Only the recombinant expression of the isoform that encodes the longest deduced amino acid sequence (OvGST3 ⁄ 5) was successful, with the purified enzyme displaying modest thiol oxidoreductase activity. Significant IgG1 and IgG4 responses against recombinantly expressed OvGST3 ⁄ 5 were detected in sera from patients with the generalized as well as the chronic hyperreactive form of onchocerciasis, indicating exposure of the secreted protein to the human host's immune system and its immunogenicity. Immunohistological localization studies performed at light and electron microscopy levels support the extracellular localization of the protein. Intensive labeling of the OvGST3 was observed in the egg shell at the morula stage of the embryo, indicating extremely defined, stage-specific expression for a short transient period only.

Proteomic and Immunochemical Characterization of Glutathione Transferase as a New Allergen of the Nematode Ascaris lumbricoides

“…We found that at least six GSTA isoforms bind IgE with different intensities (Figure 6C), in agreement with findings describing that helminth GSTs exist as isoforms and their amino acid substitutions and post-translational modifications such as glycosylations may influence their immunogenicity [20], [31]–[33]. Previous studies in A. suum have detected most of the GST expression in the brush border of the parasite's gut and weak to moderate expression in the cytoplasm of longitudinal muscle cells, oviducts and the lateral cords of the hypodermis [34].…”

Comparative Analysis of the Secretome from a Model Filarial Nematode (Litomosoides sigmodontis) Reveals Maximal Diversity in Gravid Female Parasites

“…From our data, we suggest that vulval excretion is the main source of ESP proteins in gAF and pgAF, and that the iMf are coated with proteins secreted by the uterine epithelium. This interpretation is supported not only by the abundance of MSPs and vitellogenin in gAF and pgAF ESP, but by the presence of omegaclass secreted GST isoforms exclusively in gAF ESP, which in O. volvulus are only produced by embryos at the morula stage (44). Similarly, ESP proteins in the male nematode probably originate primarily from seminal fluid.…”

“…Functionally defined components of the ESP included a small cysteine proteinase inhibitor [CPI (43)], the omega-class glutathione S-transferases [GST (44)], the MSPs (45), and the microfilarial sheath protein (46) (Fig. 5B).…”

Glutathione-S-Transferases in the Olfactory Organ of the Noctuid Moth Spodoptera littoralis, Diversity and Conservation of Chemosensory Clades

“…More globally, our extensive analysis of signal peptide presence in GSTs from various insect orders revealed that this structural feature is more widely spread than suspected and not restricted to delta GSTs, as we found also a SP in an antennal GST sigma from a coleopteran species. Extracellular GSTs have been previously characterized in several Nematodes species (Sommer et al, 2001; Liebau et al, 2008; Espada et al, 2016b), and in the pine wood nematode Bursaphelenchus xylophilus ; one of these enzyme metabolize various terpenoid compounds (Espada et al, 2016a), also known as common odorant molecules for insects. These antennal GSTs could thus be secreted in the sensillar lymph surrounding the sensory neurons, where they would directly interact with their relative substrate.…”