# Structural and Functional Insights into the Delivery Systems of Bacillus and Clostridial Binary Toxins

## TL;DR

This paper reviews how certain bacteria use binary toxins to damage host cells, focusing on the structure and function of the delivery components of these toxins.

## Contribution

The paper provides structural insights into the B subunits of binary toxins from Bacillus and Clostridial species, enhancing understanding of toxin delivery mechanisms.

## Key findings

- Structural elucidation of B subunits reveals how they facilitate toxin delivery into host cells.
- Binary toxins from Bacillus thuringiensis, Clostridioides difficile, and Clostridium perfringens are compared in terms of their delivery mechanisms.
- Findings help explain how these toxins cause rapid host cell death by ADP-ribosylating actin.

## Abstract

Pathogenic Bacillus and clostridial (i.e., Clostridium and Clostridioides) bacteria express a diverse repertoire of effector proteins to promote disease. This includes production of binary toxins, which enter host epithelial cells and seriously damage the intestinal tracts of insects, animals, and humans. In particular, binary toxins form an AB-type complex composed of a catalytic subunit that is toxic (A) and an oligomeric cell-binding and delivery subunit (B), where upon delivery of A into the cytoplasm of the host cell it catalytically ADP-ribosylates actin and rapidly induces host cell death. In this review, binary toxins expressed by Bacillus thuringiensis, Clostridioides difficile, and Clostridium perfringens will be discussed, with particular focus placed upon the structural elucidations of their respective B subunits and how these findings help to deconvolute how toxic enzyme delivery into target host cells is achieved by these deadly bacteria.