Functional Characterization of an Extended Binding Component of the Actin-ADP-Ribosylating C2 Toxin Detected in Clostridium botulinum Strain (C) 2300

Abstract

Clostridium botulinum C2 toxin consists of the binding component C2II and the enzyme component C2I, which ADP-ribosylates G-actin of eukaryotic cells. Trypsin-activated C2II (C2IIa) forms heptamers that mediate cell binding and translocation of C2I from acidic endosomes into the cytosol of target cells. By genome sequencing of C. botulinum strain (C) 2300, we found that C2II from this strain carries a C-terminal extension of 129 amino acids, unlike its homologous counterparts from strains (C) 203U28, (C) 468, and (D) 1873. This extension shows a high similarity to the C-terminal receptor-binding domain of C2II and is presumably the result of a duplication of this domain. The C2II extension facilitates the binding to cell surface receptors, which leads to an increased intoxication efficiency compared to that of C2II proteins from other C. botulinum strains.

Cyclophilin-Facilitated Membrane Translocation as Pharmacological Target to Prevent Intoxication of Mammalian Cells by Binary Clostridial Actin ADP-Ribosylated Toxins

“…The cellular uptake of C2 and iota toxins was discovered by us and by others during recent years. C2 toxin consists of the enzyme component C2I (~49 kDa) [31,32] and the binding/translocation component C2II (~80 or 100 kDa, depending on the strain [33,34]). Proteolytically activated C2II forms ring-shaped heptamers (C2IIa) that bind to asparagine-linked carbohydrate structures on mammalian cells [30,33,[35][36][37] and form complexes with C2I.…”

Structural constraints-based evaluation of immunogenic avirulent toxins from Clostridium botulinum C2 and C3 toxins as subunit vaccines

“…We have shown that secondary structural elements particularly helices and sheets are not altered upon a point mutation, but the loops/coils are reorganized from the native states. Catalytic and binding sites are generally located in the coil and loops of C2 and C3 (Aktories and Barth, 2004;Barth et al, 1998;Kowarsch et al, 2010;Sterthoff et al, 2010). A mutational constraint in those sites may bring conformational flexibility in loop and coils which in turn to decrease in NADbinding affinity and catalytic function.…”

Interaction of the Clostridium difficile Binary Toxin CDT and Its Host Cell Receptor, Lipolysis-stimulated Lipoprotein Receptor (LSR)

“…CDTb was obtained by proteolytic activation of pCDTb (11,34). If not otherwise stated, 1 nM CDTa together with 0.2 nM CDTb were added to cultured cells for intoxication experiments.…”