# Bordetella BcrH1 and BcrH2 Are Specific Chaperones for the Pore‐Forming Complex

## TL;DR

This study shows that BcrH1 and BcrH2 are specific chaperones that help maintain the stability of proteins involved in forming pores in host membranes during Bordetella infection.

## Contribution

The study identifies BcrH1 and BcrH2 as specific chaperones for BopB and BopD in the Bordetella type III secretion system.

## Key findings

- BcrH1 and BcrH2 are specific chaperones for BopB and BopD, respectively.
- Deficiency in BcrH1 or BcrH2 reduces the levels of BopB and BopD in bacterial cells.
- BcrH1 and BcrH2 deficiencies lead to reduced hemolytic activity and cell toxicity.

## Abstract

Bordetella has a type III secretion system that secretes virulence proteins crucial to the establishment of infection. The genes encoding components of the Bordetella type III secretion system are located in the bsc region on the chromosome. This region includes the bcrH1 and bcrH2 genes, which respectively encode the proteins BcrH1 and BcrH2. In this study, we analyzed the functions of BcrH1 and BcrH2 in the Bordetella type III secretion system. First, we created a BcrH1‐deficient strain and a BcrH2‐deficient strain. We analyzed the amounts of the type III secreted proteins BopB and BopD, which make a complex that forms pores in the host membrane, in bacterial cells of each protein‐deficient strain. The results showed that the BopB and BopD signals were weakened in the whole cell fraction of the BcrH1‐deficient strain and the BcrH2‐deficient strain, respectively. The hemolytic activity and cell toxicity of each BcrH protein‐deficient strain were significantly lower than those of the wild‐type strain. When anti‐BcrH1 and anti‐BcrH2 antibodies were used for the immunoprecipitation assay, the BopB and BopD signals were detected in the precipitated fractions, respectively. These results strongly suggest that BcrH1 and BcrH2 are specific chaperones for maintaining the stability of BopB and BopD, respectively.