Biomphalysin, a New β Pore-forming Toxin Involved in Biomphalaria glabrata Immune Defense against Schistosoma mansoni

Abstract

Aerolysins are virulence factors belonging to the β pore-forming toxin (β-PFT) superfamily that are abundantly distributed in bacteria. More rarely, β-PFTs have been described in eukaryotic organisms. Recently, we identified a putative cytolytic protein in the snail, Biomphalaria glabrata, whose primary structural features suggest that it could belong to this β-PFT superfamily. In the present paper, we report the molecular cloning and functional characterization of this protein, which we call Biomphalysin, and demonstrate that it is indeed a new eukaryotic β-PFT. We show that, despite weak sequence similarities with aerolysins, Biomphalysin shares a common architecture with proteins belonging to this superfamily. A phylogenetic approach revealed that the gene encoding Biomphalysin could have resulted from horizontal transfer. Its expression is restricted to immune-competent cells and is not induced by parasite challenge. Recombinant Biomphalysin showed hemolytic activity that was greatly enhanced by the plasma compartment of B. glabrata. We further demonstrated that Biomphalysin with plasma is highly toxic toward Schistosoma mansoni sporocysts. Using in vitro binding assays in conjunction with Western blot and immunocytochemistry analyses, we also showed that Biomphalysin binds to parasite membranes. Finally, we showed that, in contrast to what has been reported for most other members of the family, lytic activity of Biomphalysin is not dependent on proteolytic processing. These results provide the first functional description of a mollusk immune effector protein involved in killing S. mansoni.

Digenean-gastropod host associations inform on aspects of specific immunity in snails

“…The advent of routine automated DNA sequencing afforded gene discovery through random expressed sequence tags (ESTs) and this drove a large number of studies (an incomplete yet representative listing includes e.g. : Hanelt et al, 2008, Lockyer et al, 2007, Mitta er al., 2005, Raghavan et al, 2003) that provide identification of many additional putative immune factors of B. glabrata , (e.g Baron et al, 2013; Galinier et al, 2013; Garcia et al, 2010; Guillou et al, 2004; Yoshino et al, 2008), revealing potential immune mechanism that could be studied further for a better understanding of snail immunity. This trend continues with the imminent characterization of the B. glabrata genome.…”

Endogenous growth factor stimulation of hemocyte proliferation induces resistance to Schistosoma mansoni challenge in the snail host

“…Underpinning this impressive change in infection outcome is a significant increase in the generation of circulating adherent hemocytes, which is the hemocyte subset that participates in the encapsulation of S. mansoni sporocysts (10). Adherent hemocytes are also highly phagocytic (2) and are responsible for the production of reactive and nitrogen intermediates (11) and soluble immune factors that are important for successful clearance of digenetic trematodes (1,2). This cell population nearly doubled following administration of rBgGRN.…”

“…Studies investigating compatibility between Biomphalaria snails and S. mansoni suggest that the snail immune response plays a crucial role in determining infection outcome. Although circulating humoral factors are known to play an important role in determining infection outcome via recognition of various parasite targets, or by directly damaging the parasite tegument (1)(2)(3)(4), it is ultimately the immune cells of the snail, known as hemocytes, that are primarily responsible for encapsulating and eliminating the parasite (5).…”

No more non-model species: The promise of next generation sequencing for comparative immunology

“…However, this approach has been limited by the relatively shallow depth of sequence diversity that can be assessed using cDNA microarrays. In contrast, mRNA sequencing by NGS generates millions of cDNA fragments (reads) and mRNA expression can be rapidly evaluated by counting the number of reads that match the gene or transcript of interest in the corresponding genome or transcriptome, even though candidate sequences still require functional validation of immune function and involvement (Galinier et al 2013). The ever decreasing cost of RNA sequencing also implies that kinetic studies are being possible, which will considerably enhance biological significance of gene expression studies.…”