Structural dynamics of the CROPs domain control stability and toxicity of Paeniclostridium sordellii lethal toxin

Abstract

Paeniclostridium sordellii lethal toxin (TcsL) is a potent exotoxin that causes lethal toxic shock syndrome associated with fulminant bacterial infections. TcsL belongs to the large clostridial toxin (LCT) family. Here, we report that TcsL with varied lengths of combined repetitive oligopeptides (CROPs) deleted show increased autoproteolysis as well as higher cytotoxicity. We next present cryo-EM structures of full-length TcsL, at neutral (pH 7.4) and acidic (pH 5.0) conditions. The TcsL at neutral pH exhibits in the open conformation, which resembles reported TcdB structures. Low pH induces the conformational change of partial TcsL to the closed form. Two intracellular interfaces are observed in the closed conformation, which possibly locks the cysteine protease domain and hinders the binding of the host receptor. Our findings provide insights into the structure and function of TcsL and reveal mechanisms for CROPs-mediated modulation of autoproteolysis and cytotoxicity, which could be common across the LCT family.

Molecular basis of TMPRSS2 recognition by Paeniclostridium sordellii hemorrhagic toxin

“…Recent studies have resolved the high-resolution structures of full-length TcdB 22 , 24 , 25 , full-length TcsL 26 , and near-complete TcdA 20 , 21 . Despite these important achievements, architectural insights into other LCT members are still lacking.…”

“…Researchers have made encouraging progress in resolving the full-length or near-complete structures of LCTs including TcdA 20 , 21 , TcdB 22 – 25 , and TcsL 26 . At neutral pH, TcdA displays in a “closed” conformation that the CROPs domain curves downward alongside the DRBD, while TcdB and TcsL present in an “open” conformation that the CROPs domain curves upward around the GTD-CPD head.…”

“…At neutral pH, TcdA displays in a “closed” conformation that the CROPs domain curves downward alongside the DRBD, while TcdB and TcsL present in an “open” conformation that the CROPs domain curves upward around the GTD-CPD head. Under the low-pH condition, the structures of TcdB and TcsL would convert from the open to closed conformation 22 , 26 . Little is known about the full-length structure of TcsH.…”

Overview of Bacterial Protein Toxins from Pathogenic Bacteria: Mode of Action and Insights into Evolution

“…Single-chain protein toxins from the large clostridial glucosylating toxins (LCGTs) such as C. difficile TcdA and TcdB contain a cysteine protease domain (CPD), which cleaves the catalytic domain from the rest of the molecule during the translocation of A through the endosomal membrane. The C-terminal part of LCGTs contains repetitive sequences (combined repetitive oligopeptides, CROPs), which in closed conformation prevent CPD-dependent autoprocessing, whereas the open conformation is suitable for toxin binding to the receptor and CPD interaction [ 197 , 198 , 199 ]. In the AB 5 toxins, the A fragment is proteolytically cleaved into A1 and A2, which are linked by a disulfide bridge.…”