Abstract
Vibrio cholerae cytolysin (VCC) is a prominent member in the family of β-barrel pore-forming toxins. It induces lysis of target eukaryotic cells by forming transmembrane oligomeric β-barrel channels. VCC also exhibits prominent lectin-like activity in interacting with β1-galactosyl-terminated glycoconjugates. Apart from the cytolysin domain, VCC harbors two lectin-like domains: the β-Trefoil and the β-Prism domains; however, precise contribution of these domains in the lectin property of VCC is not known. Also, role(s) of these lectin-like domains in the mode of action of VCC remain obscure. In the present study, we show that the β-Prism domain of VCC acts as the structural scaffold to determine the lectin activity of the protein toward β1-galactosyl-terminated glycoconjugates. Toward exploring the physiological implication of the β-Prism domain, we demonstrate that the presence of the β-Prism domain-mediated lectin activity is crucial for an efficient interaction of the toxin toward the target cells. Our results also suggest that such lectin activity may act to regulate the oligomerization ability of the membrane-bound VCC toxin. Based on the data presented here, and also consistent with the existing structural information, we propose a novel mechanism of regulation imposed by the β-Prism domain's lectin activity, implicated in the process of membrane pore formation by VCC.
Highlights
Vibrio cholerae cytolysin is a pore-forming toxin with lectin-like activity
11 tryptophan residues distributed throughout the protein structure; two of these are located within the -Prism domain) and far-UV circular dichroism (CD) profile of the Vibrio cholerae cytolysin (VCC)-⌬-Prism variant confirmed folding and structural integrity of the -Prism-deleted protein
The observed differences in the hemolytic activity of the VCC-⌬-Prism proteins, as reported in the present study and in the earlier reports, could be attributed to the differential susceptibility of the human and rabbit erythrocytes toward VCC-mediated cytotoxicity. When compared with those of the full-length VCC protein, the VCC⌬-Prism variant displayed overall similar intrinsic tryptophan fluorescence emission spectra and far-UV circular dichroism (CD) profile (Fig. 1E)
Summary
Vibrio cholerae cytolysin is a pore-forming toxin with lectin-like activity. Results: -Prism domain mediates the lectin activity, which determines efficient membrane binding and modulates membrane oligomerization of the toxin. Vibrio cholerae cytolysin (VCC) is a prominent member in the family of -barrel pore-forming toxins. We show that the -Prism domain of VCC acts as the structural scaffold to determine the lectin activity of the protein toward 1-galactosyl-terminated glycoconjugates. Toward exploring further the physiological implication of the lectin activity of the -Prism domain, we have shown that the -Prism domain-mediated lectin activity plays a critical role in targeting the VCC toxin toward the erythrocyte membrane. We hypothesize that the -Prism domain-mediated lectin activity may act as a crucial triggering mechanism so as to allow formation of the VCC oligomeric assembly in the target cell membrane. Our study provides novel insights regarding critical implications of the -Prism domain-mediated lectin activity for the mode of action of VCC
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