Bcr4 Is a Chaperone for the Inner Rod Protein in the Bordetella Type III Secretion System
ABSTRACT Bordetella bronchiseptica injects virulence proteins called effectors into host cells via a type III secretion system (T3SS) conserved among many Gram-negative bacteria. Small proteins called chaperones are required to stabilize some T3SS components or localize them to the T3SS machinery. I...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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American Society for Microbiology
2022-10-01
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| Series: | Microbiology Spectrum |
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| Online Access: | https://journals.asm.org/doi/10.1128/spectrum.01443-22 |
| _version_ | 1797990002798362624 |
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| author | Masataka Goto Akio Abe Tomoko Hanawa Masato Suzuki Asaomi Kuwae |
| author_facet | Masataka Goto Akio Abe Tomoko Hanawa Masato Suzuki Asaomi Kuwae |
| author_sort | Masataka Goto |
| collection | DOAJ |
| description | ABSTRACT Bordetella bronchiseptica injects virulence proteins called effectors into host cells via a type III secretion system (T3SS) conserved among many Gram-negative bacteria. Small proteins called chaperones are required to stabilize some T3SS components or localize them to the T3SS machinery. In a previous study, we identified a chaperone-like protein named Bcr4 that regulates T3SS activity in B. bronchiseptica. Bcr4 does not show strong sequence similarity to well-studied T3SS proteins of other bacteria, and its function remains to be elucidated. Here, we investigated the mechanism by which Bcr4 controls T3SS activity. A pulldown assay revealed that Bcr4 interacts with BscI, based on its homology to other bacterial proteins, to be an inner rod protein of the T3SS machinery. An additional pulldown assay using truncated Bcr4 derivatives and secretion profiles of B. bronchiseptica producing truncated Bcr4 derivatives showed that the Bcr4 C-terminal region is necessary for the interaction with BscI and activation of the T3SS. Moreover, the deletion of BscI abolished the secretion of type III secreted proteins from B. bronchiseptica and the translocation of a cytotoxic effector into cultured mammalian cells. Finally, we show that BscI is unstable in the absence of Bcr4. These results suggest that Bcr4 supports the construction of the T3SS machinery by stabilizing BscI. This is the first demonstration of a chaperone for the T3SS inner rod protein among the virulence bacteria possessing the T3SS. IMPORTANCE The type III secretion system (T3SS) is a needle-like complex that projects outward from bacterial cells. Bordetella bronchiseptica uses the T3SS to inject virulence proteins into host cells. Our previous study reported that a protein named Bcr4 is essential for the secretion of virulence proteins from B. bronchiseptica bacterial cells and delivery through the T3SS. Because other bacteria lack a Bcr4 homologue, the function of Bcr4 has not been elucidated. In this study, we discovered that Bcr4 interacts with BscI, a component of the T3SS machinery. We show that a B. bronchiseptica BscI-deficient strain was unable to secrete type III secreted proteins. Furthermore, in a B. bronchiseptica strain that overproduces T3SS component proteins, Bcr4 is required to maintain BscI in bacterial cells. These results suggest that Bcr4 stabilizes BscI to allow construction of the T3SS in B. bronchiseptica. |
| first_indexed | 2024-04-11T08:28:27Z |
| format | Article |
| id | doaj.art-f0afa0f66a744112941332859e531500 |
| institution | Directory Open Access Journal |
| issn | 2165-0497 |
| language | English |
| last_indexed | 2024-04-11T08:28:27Z |
| publishDate | 2022-10-01 |
| publisher | American Society for Microbiology |
| record_format | Article |
| series | Microbiology Spectrum |
| spelling | doaj.art-f0afa0f66a744112941332859e5315002022-12-22T04:34:37ZengAmerican Society for MicrobiologyMicrobiology Spectrum2165-04972022-10-0110510.1128/spectrum.01443-22Bcr4 Is a Chaperone for the Inner Rod Protein in the Bordetella Type III Secretion SystemMasataka Goto0Akio Abe1Tomoko Hanawa2Masato Suzuki3Asaomi Kuwae4Laboratory of Bacterial Infection, Graduate School of Infection Control Sciences, Kitasato University, Tokyo, JapanLaboratory of Bacterial Infection, Graduate School of Infection Control Sciences, Kitasato University, Tokyo, JapanDepartment of Infectious Diseases, Kyorin University School of Medicine, Tokyo, JapanAntimicrobial Resistance Research Center, National Institute of Infectious Diseases, Tokyo, JapanLaboratory of Bacterial Infection, Graduate School of Infection Control Sciences, Kitasato University, Tokyo, JapanABSTRACT Bordetella bronchiseptica injects virulence proteins called effectors into host cells via a type III secretion system (T3SS) conserved among many Gram-negative bacteria. Small proteins called chaperones are required to stabilize some T3SS components or localize them to the T3SS machinery. In a previous study, we identified a chaperone-like protein named Bcr4 that regulates T3SS activity in B. bronchiseptica. Bcr4 does not show strong sequence similarity to well-studied T3SS proteins of other bacteria, and its function remains to be elucidated. Here, we investigated the mechanism by which Bcr4 controls T3SS activity. A pulldown assay revealed that Bcr4 interacts with BscI, based on its homology to other bacterial proteins, to be an inner rod protein of the T3SS machinery. An additional pulldown assay using truncated Bcr4 derivatives and secretion profiles of B. bronchiseptica producing truncated Bcr4 derivatives showed that the Bcr4 C-terminal region is necessary for the interaction with BscI and activation of the T3SS. Moreover, the deletion of BscI abolished the secretion of type III secreted proteins from B. bronchiseptica and the translocation of a cytotoxic effector into cultured mammalian cells. Finally, we show that BscI is unstable in the absence of Bcr4. These results suggest that Bcr4 supports the construction of the T3SS machinery by stabilizing BscI. This is the first demonstration of a chaperone for the T3SS inner rod protein among the virulence bacteria possessing the T3SS. IMPORTANCE The type III secretion system (T3SS) is a needle-like complex that projects outward from bacterial cells. Bordetella bronchiseptica uses the T3SS to inject virulence proteins into host cells. Our previous study reported that a protein named Bcr4 is essential for the secretion of virulence proteins from B. bronchiseptica bacterial cells and delivery through the T3SS. Because other bacteria lack a Bcr4 homologue, the function of Bcr4 has not been elucidated. In this study, we discovered that Bcr4 interacts with BscI, a component of the T3SS machinery. We show that a B. bronchiseptica BscI-deficient strain was unable to secrete type III secreted proteins. Furthermore, in a B. bronchiseptica strain that overproduces T3SS component proteins, Bcr4 is required to maintain BscI in bacterial cells. These results suggest that Bcr4 stabilizes BscI to allow construction of the T3SS in B. bronchiseptica.https://journals.asm.org/doi/10.1128/spectrum.01443-22Bcr4BordetellaBscIT3SSchaperoneinner rod |
| spellingShingle | Masataka Goto Akio Abe Tomoko Hanawa Masato Suzuki Asaomi Kuwae Bcr4 Is a Chaperone for the Inner Rod Protein in the Bordetella Type III Secretion System Microbiology Spectrum Bcr4 Bordetella BscI T3SS chaperone inner rod |
| title | Bcr4 Is a Chaperone for the Inner Rod Protein in the Bordetella Type III Secretion System |
| title_full | Bcr4 Is a Chaperone for the Inner Rod Protein in the Bordetella Type III Secretion System |
| title_fullStr | Bcr4 Is a Chaperone for the Inner Rod Protein in the Bordetella Type III Secretion System |
| title_full_unstemmed | Bcr4 Is a Chaperone for the Inner Rod Protein in the Bordetella Type III Secretion System |
| title_short | Bcr4 Is a Chaperone for the Inner Rod Protein in the Bordetella Type III Secretion System |
| title_sort | bcr4 is a chaperone for the inner rod protein in the bordetella type iii secretion system |
| topic | Bcr4 Bordetella BscI T3SS chaperone inner rod |
| url | https://journals.asm.org/doi/10.1128/spectrum.01443-22 |
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