LRP1 is a receptor for Clostridium perfringens TpeL toxin indicating a two-receptor model of clostridial glycosylating toxins

Abstract

Large glycosylating toxins are major virulence factors of various species of pathogenic Clostridia. Prototypes are Clostridium difficile toxins A and B, which cause antibiotics-associated diarrhea and pseudomembranous colitis. The current model of the toxins' action suggests that receptor binding is mediated by a C-terminal domain of combined repetitive oligopeptides (CROP). This model is challenged by the glycosylating Clostridium perfringens large cytotoxin (TpeL toxin) that is devoid of the CROP domain but still intoxicates cells. Using a haploid genetic screen, we identified LDL receptor-related protein 1 (LRP1) as a host cell receptor for the TpeL toxin. LRP1-deficient cells are not able to take up TpeL and are not intoxicated. Expression of cluster IV of LRP1 is sufficient to rescue toxin uptake in these cells. By plasmon resonance spectroscopy, a K D value of 23 nM was determined for binding of TpeL to LRP1 cluster IV. The C terminus of TpeL (residues 1335-1779) represents the receptor-binding domain (RBD) of the toxin. RBD-like regions are conserved in all other clostridial glycosylating toxins preceding their CROP domain. CROP-deficient C. difficile toxin B is toxic to cells, depending on the RBD-like region (residues 1349-1811) but does not interact with LRP1. Our data indicate the presence of a second, CROP-independent receptor-binding domain in clostridial glycosylating toxins and suggest a two-receptor model for the cellular uptake of clostridial glycosylating toxins.toxin receptor | receptor-mediated endocytosis

Toxin-Mediated Paracellular Transport of Antitoxin Antibodies Facilitates Protection against Clostridium difficile Infection

“…It is thought that both toxins bind to target mammalian cells (typically gut epithelial cells) at least in part through their C-terminal receptor-binding domains (combined repetitive oligopeptide [CROP] domains) and become internalized via receptor-mediated endocytosis (6,7). Following internalization, acidification of the endosome leads to a conformational change within the toxins that results in translocation of the glucosyltransferase domain (GTD) across the endosomal membrane and autocleavage via the cysteine protease domain (8)(9)(10).…”

Mechanism of Action and Epitopes of Clostridium difficile Toxin B-neutralizing Antibody Bezlotoxumab Revealed by X-ray Crystallography

“…Evidence that the receptor for TcdB is also a carbohydrate is currently limited to the observation that this toxin is structurally highly homologous to TcdA (7,17) and that it binds to carbohydrates that are structurally related to the TcdA ligands (10,11). It is thought that toxin binding to receptor(s) on the cell surface occurs via the C-terminal domain of the toxins (known as the combined repetitive oligopeptide (CROP) domain) (12,(17)(18)(19), although recent data suggest that other domains within the toxins may also be involved in binding (20,21). Analysis of the sequences of the TcdA and TcdB CROP domains shows that they consist of ϳ20 -30 short repeats (SRs) interspersed with a smaller number (seven in TcdA and four in TcdB) of homologous long repeats (LRs) (12,17,22,23).…”

Clostridium difficile Infection

“…Indeed, TcdA and TcdB lacking CROPS domains are still capable of intoxicating cells 113,114 , and the homologous toxin TpeL from Clostridium perfringens lacks a CROPS domain entirely 115 . Recently, two protein receptors have been reported for TcdB: poliovirus receptor-like protein 3 (PVRL3; also called nectin 3) 116 and chondroitin sulfate proteoglycan 4 (CSPG4) 117 .…”