Clostridial hemolysin β-pore-forming toxins: from genomic insights to receptor specificity and clinical implications

Several clostridial species can cause severe diseases in humans and animals. Among their most frequent virulence factors are hemolysin β-pore-forming toxins (β-PFTs). These protein toxins are secreted as soluble monomers that oligomerize on host cell membranes to form membrane-inserted β-barrel pores. Recent research on bacterial hemolysin β-PFTs showed that many, including those secreted by clostridia, target their host cells via specific membrane protein receptors. To date, 14 hemolysin β-PFTs and related homologs have been identified in different Clostridium species, most of which remain uncharacterized. Here we report 11 additional putative hemolysin β-PFT homologs identified across six Clostridium species through database analyses. We reviewed knowledge from genomic, in vitro and in vivo studies on clostridial hemolysin β-PFTs, with emphasis on toxin-host cell recognition and the roles in the pathogenesis of diseases.