Abstract
Clostridium perfringens is a potent producer of a variety of toxins. Well studied from these are five toxins (alpha, Beta (CPB), epsilon, iota and CPE) that are produced by seven toxinotype strains (A–G) of C. perfringens. Besides these toxins, C. perfringens produces also another toxin that causes necrotizing enterocolitis in piglets. This toxin termed consensus Beta2 toxin (cCPB2) has a molecular mass of 27,620 Da and shows only little homology to CPB and no one to the other toxins of C. perfringens. Its primary action on cells remained unknown to date. cCPB2 was heterogeneously expressed as fusion protein with GST in Escherichia coli and purified to homogeneity. Although cCPB2 does not exhibit the typical structure of beta-stranded pore-forming proteins and contains no indication for the presence of amphipathic alpha-helices we could demonstrate that cCPB2 is a pore-forming component with an extremely high activity in lipid bilayers. The channels have a single-channel conductance of about 700 pS in 1 M KCl and are highly cation-selective as judged from selectivity measurements in the presence of salt gradients. The high cation selectivity is caused by the presence of net negative charges in or near the channel that allowed an estimate of the channel size being about 1.4 nm wide. Our measurements suggest that the primary effect of cCPB2 is the formation of cation-selective channels followed by necrotic enteritis in humans and animals. We searched in databases for homologs of cCPB2 and constructed a cladogram representing the phylogenetic relationship to the next relatives of cCPB2.
Highlights
Clostridium perfringens consensus Beta2 toxin has been first identified as the unique virulence factor of a C. perfringens strain isolated from a piglet neonatal necrotic enteritis (Gibert et al 1997). Consensus Clostridium perfringens Beta2 toxin (cCPB2) shows a low amino acid sequence identity with C. perfringens Beta toxin (CPB) which is characteristic of C. perfringens types B and C and which is responsible for necrotic enteritis notably in young animals (Songer 2010; Uzal et al 2010; Rood et al 2018)
We show that cCPB2 is a poreforming toxins (PFT) which forms cationselective channels of about 1.4 nm diameter in lipid bilayers
The lack of predicted long alpha-helical structures in cCPB2 amino acid sequence suggests that cCPB2 does not belong to the family of toxins, where the channels are lined up by α-helices (α-PFTs)
Summary
Clostridium perfringens consensus Beta toxin (cCPB2) has been first identified as the unique virulence factor of a C. perfringens strain isolated from a piglet neonatal necrotic enteritis (Gibert et al 1997). cCPB2 shows a low amino acid sequence identity (less than 15%) with C. perfringens Beta toxin (CPB) which is characteristic of C. perfringens types B and C and which is responsible for necrotic enteritis notably in young animals (Songer 2010; Uzal et al 2010; Rood et al 2018). CCPB2 shows a low amino acid sequence identity (less than 15%) with C. perfringens Beta toxin (CPB) which is characteristic of C. perfringens types B and C and which is responsible for necrotic enteritis notably in young animals (Songer 2010; Uzal et al 2010; Rood et al 2018). A frameshift in acpb gene in some C. perfringens strains results in the expression of a truncated CPB2 (Jost et al 2005; Vilei et al 2005). This might explain the absence of CPB2 effects in these strains. Albeit associations of C. perfringens harboring cpb with intestinal diseases have been described, the role of cCPB2 and aCPB2 in pathogenesis remains unclear (van Asten et al 2010; Schotte et al 2004)
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