The C. difficile toxin B membrane translocation machinery is an evolutionarily conserved protein delivery apparatus

Nat Commun. 2020 Jan 23;11(1):432. doi: 10.1038/s41467-020-14306-z.


Large Clostridial Toxins (LCTs) are a family of six homologous protein toxins that are implicated in severe disease. LCTs infiltrate host cells using a translocation domain (LCT-T) that contains both cell-surface receptor binding sites and a membrane translocation apparatus. Despite much effort, LCT translocation remains poorly understood. Here we report the identification of 1104 LCT-T homologs, with 769 proteins from bacteria outside of clostridia. Sequences are widely distributed in pathogenic and host-associated species, in a variety of contexts and architectures. Consistent with these homologs being functional toxins, we show that a distant LCT-T homolog from Serratia marcescens acts as a pH-dependent translocase to deliver its effector into host cells. Based on evolutionary footprinting of LCT-T homologs, we further define an evolutionarily conserved translocase region that we show is an autonomous translocase capable of delivering heterologous cargo into host cells. Our work uncovers a broad class of translocating toxins and provides insights into LCT translocation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Bacterial Toxins / chemistry*
  • Bacterial Toxins / genetics
  • Bacterial Toxins / metabolism*
  • Biological Evolution*
  • Chlorocebus aethiops
  • Circular Dichroism
  • Clostridioides difficile / metabolism*
  • Clostridioides difficile / pathogenicity
  • Conserved Sequence
  • Evolution, Molecular
  • HCT116 Cells
  • Host-Pathogen Interactions
  • Humans
  • Hydrogen-Ion Concentration
  • Protein Domains
  • Protein Transport
  • Sequence Homology, Amino Acid
  • Serratia marcescens / metabolism
  • Serratia marcescens / pathogenicity
  • Vero Cells


  • Bacterial Proteins
  • Bacterial Toxins
  • toxB protein, Clostridium difficile