Role of Autocleavage in the Function of a Type III Secretion Specificity Switch Protein in <named-content content-type="genus-species">Salmonella enterica</named-content> Serovar Typhimurium
ABSTRACT Type III secretion systems (T3SSs) are multiprotein machines employed by many Gram-negative bacteria to inject bacterial effector proteins into eukaryotic host cells to promote bacterial survival and colonization. The core unit of T3SSs is the needle complex, a supramolecular structure that...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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American Society for Microbiology
2015-10-01
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| Series: | mBio |
| Online Access: | https://journals.asm.org/doi/10.1128/mBio.01459-15 |
| _version_ | 1819010170056867840 |
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| author | Julia V. Monjarás Feria Matthew D. Lefebre York-Dieter Stierhof Jorge E. Galán Samuel Wagner |
| author_facet | Julia V. Monjarás Feria Matthew D. Lefebre York-Dieter Stierhof Jorge E. Galán Samuel Wagner |
| author_sort | Julia V. Monjarás Feria |
| collection | DOAJ |
| description | ABSTRACT Type III secretion systems (T3SSs) are multiprotein machines employed by many Gram-negative bacteria to inject bacterial effector proteins into eukaryotic host cells to promote bacterial survival and colonization. The core unit of T3SSs is the needle complex, a supramolecular structure that mediates the passage of the secreted proteins through the bacterial envelope. A distinct feature of the T3SS is that protein export occurs in a strictly hierarchical manner in which proteins destined to form the needle complex filament and associated structures are secreted first, followed by the secretion of effectors and the proteins that will facilitate their translocation through the target host cell membrane. The secretion hierarchy is established by complex mechanisms that involve several T3SS-associated components, including the “switch protein,” a highly conserved, inner membrane protease that undergoes autocatalytic cleavage. It has been proposed that the autocleavage of the switch protein is the trigger for substrate switching. We show here that autocleavage of the Salmonella enterica serovar Typhimurium switch protein SpaS is an unregulated process that occurs after its folding and before its incorporation into the needle complex. Needle complexes assembled with a precleaved form of SpaS function in a manner indistinguishable from that of the wild-type form. Furthermore, an engineered mutant of SpaS that is processed by an external protease also displays wild-type function. These results demonstrate that the cleavage event per se does not provide a signal for substrate switching but support the hypothesis that cleavage allows the proper conformation of SpaS to render it competent for its switching function. IMPORTANCE Bacterial interaction with eukaryotic hosts often involves complex molecular machines for targeted delivery of bacterial effector proteins. One such machine, the type III secretion system of some Gram-negative bacteria, serves to inject a multitude of structurally diverse bacterial proteins into the host cell. Critical to the function of these systems is their ability to secrete proteins in a strict hierarchical order, but it is unclear how the mechanism of switching works. Central to the switching mechanism is a highly conserved inner membrane protease that undergoes autocatalytic cleavage. Although it has been suggested previously that the autocleavage event is the trigger for substrate switching, we show here that this is not the case. Rather, our results show that cleavage allows the proper conformation of the protein to render it competent for its switching function. These findings may help develop inhibitors of type III secretion machines that offer novel therapeutic avenues to treat various infectious diseases. |
| first_indexed | 2024-12-21T01:08:00Z |
| format | Article |
| id | doaj.art-bd0e2f85677645efbd588663fc803ddb |
| institution | Directory Open Access Journal |
| issn | 2150-7511 |
| language | English |
| last_indexed | 2024-12-21T01:08:00Z |
| publishDate | 2015-10-01 |
| publisher | American Society for Microbiology |
| record_format | Article |
| series | mBio |
| spelling | doaj.art-bd0e2f85677645efbd588663fc803ddb2022-12-21T19:21:00ZengAmerican Society for MicrobiologymBio2150-75112015-10-016510.1128/mBio.01459-15Role of Autocleavage in the Function of a Type III Secretion Specificity Switch Protein in <named-content content-type="genus-species">Salmonella enterica</named-content> Serovar TyphimuriumJulia V. Monjarás Feria0Matthew D. Lefebre1York-Dieter Stierhof2Jorge E. Galán3Samuel Wagner4Interfaculty Institute of Microbiology and Infection Medicine (IMIT), University of Tübingen, Tübingen, GermanyDepartment of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut, USACenter for Plant Molecular Biology (ZMBP), University of Tübingen, Tübingen, GermanyDepartment of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut, USAInterfaculty Institute of Microbiology and Infection Medicine (IMIT), University of Tübingen, Tübingen, GermanyABSTRACT Type III secretion systems (T3SSs) are multiprotein machines employed by many Gram-negative bacteria to inject bacterial effector proteins into eukaryotic host cells to promote bacterial survival and colonization. The core unit of T3SSs is the needle complex, a supramolecular structure that mediates the passage of the secreted proteins through the bacterial envelope. A distinct feature of the T3SS is that protein export occurs in a strictly hierarchical manner in which proteins destined to form the needle complex filament and associated structures are secreted first, followed by the secretion of effectors and the proteins that will facilitate their translocation through the target host cell membrane. The secretion hierarchy is established by complex mechanisms that involve several T3SS-associated components, including the “switch protein,” a highly conserved, inner membrane protease that undergoes autocatalytic cleavage. It has been proposed that the autocleavage of the switch protein is the trigger for substrate switching. We show here that autocleavage of the Salmonella enterica serovar Typhimurium switch protein SpaS is an unregulated process that occurs after its folding and before its incorporation into the needle complex. Needle complexes assembled with a precleaved form of SpaS function in a manner indistinguishable from that of the wild-type form. Furthermore, an engineered mutant of SpaS that is processed by an external protease also displays wild-type function. These results demonstrate that the cleavage event per se does not provide a signal for substrate switching but support the hypothesis that cleavage allows the proper conformation of SpaS to render it competent for its switching function. IMPORTANCE Bacterial interaction with eukaryotic hosts often involves complex molecular machines for targeted delivery of bacterial effector proteins. One such machine, the type III secretion system of some Gram-negative bacteria, serves to inject a multitude of structurally diverse bacterial proteins into the host cell. Critical to the function of these systems is their ability to secrete proteins in a strict hierarchical order, but it is unclear how the mechanism of switching works. Central to the switching mechanism is a highly conserved inner membrane protease that undergoes autocatalytic cleavage. Although it has been suggested previously that the autocleavage event is the trigger for substrate switching, we show here that this is not the case. Rather, our results show that cleavage allows the proper conformation of the protein to render it competent for its switching function. These findings may help develop inhibitors of type III secretion machines that offer novel therapeutic avenues to treat various infectious diseases.https://journals.asm.org/doi/10.1128/mBio.01459-15 |
| spellingShingle | Julia V. Monjarás Feria Matthew D. Lefebre York-Dieter Stierhof Jorge E. Galán Samuel Wagner Role of Autocleavage in the Function of a Type III Secretion Specificity Switch Protein in <named-content content-type="genus-species">Salmonella enterica</named-content> Serovar Typhimurium mBio |
| title | Role of Autocleavage in the Function of a Type III Secretion Specificity Switch Protein in <named-content content-type="genus-species">Salmonella enterica</named-content> Serovar Typhimurium |
| title_full | Role of Autocleavage in the Function of a Type III Secretion Specificity Switch Protein in <named-content content-type="genus-species">Salmonella enterica</named-content> Serovar Typhimurium |
| title_fullStr | Role of Autocleavage in the Function of a Type III Secretion Specificity Switch Protein in <named-content content-type="genus-species">Salmonella enterica</named-content> Serovar Typhimurium |
| title_full_unstemmed | Role of Autocleavage in the Function of a Type III Secretion Specificity Switch Protein in <named-content content-type="genus-species">Salmonella enterica</named-content> Serovar Typhimurium |
| title_short | Role of Autocleavage in the Function of a Type III Secretion Specificity Switch Protein in <named-content content-type="genus-species">Salmonella enterica</named-content> Serovar Typhimurium |
| title_sort | role of autocleavage in the function of a type iii secretion specificity switch protein in named content content type genus species salmonella enterica named content serovar typhimurium |
| url | https://journals.asm.org/doi/10.1128/mBio.01459-15 |
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