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Virulence mechanisms of pathogenic Yersinia: aspects of type III secretion and twin arginine translocation
Umeå University, Faculty of Medicine, Molecular Biology.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The pathogenic bacteria Yersinia pestis and Y. pseudotuberculosis are related to the degree where the former is considered a subspecies of the latter, and still they cause disease of little resemblance in humans. Y. pestis is the causative agent of lethal bubonic and pneumonic plague, while Y. pseudotuberculosis manifests itself as mild gastroenteritis. An important virulence determinant for these species is their ability to secrete and inject toxins (Yop effectors) into immune cells of the infected host, in a bacterium-cell contact dependent manner. This ability depends on the extensively studied type III secretion system, a highly complex multicomponent structure resembling a needle. The induction of Yop secretion is a strictly controlled event. The two structural type III secretion components YscU and YscP are here shown to play a crucial role in this process, which is suggested to require an YscP mediated conformational change of the C-terminus of YscU. Proteolytic cleavage of YscU within this domain is further revealed to be a prerequisite for functional Yop secretion. The needle subcomponent itself, YscF, is recognised as a regulatory element that controls the induction of Yop effectors and their polarised delivery into target cells. Potentially, the needle might act as a sensor that transmits the inducing signal (i.e. target cell contact) to activate the type III secretion system. Secondly a, for Yersinia, previously unexplored system, the Twin arginine translocation (Tat) pathway, is shown to be functional and absolutely required for virulence of Y. pseudotuberculosis. A range of putative Yersinia Tat substrates were predicted in silico, which together with the Tat system itself may be interesting targets for future development of antimicrobial treatments.

Place, publisher, year, edition, pages
Umeå: Molekylärbiologi (Teknisk-naturvetenskaplig fakultet) , 2005. , 67 p.
Keyword [en]
Molecular biology, Yersinia pestis, Yersinia pseudotuberculosis, bacterial pathogenesis, type III secretion, twin arginine translocation, virulence mechanisms, YscU, YscP, YscF
Keyword [sv]
Molekylärbiologi
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-619ISBN: 91-7305-948-X (print)OAI: oai:DiVA.org:umu-619DiVA: diva2:144012
Public defence
2005-11-25, Lecture Hall "Major Groove", 6L, NUS, Umeå Universitet, 901 87 Umeå, 10:00
Opponent
Supervisors
Available from: 2005-10-27 Created: 2005-10-27Bibliographically approved
List of papers
1. The Twin Arginine Translocation System is Essential for Virulence of Yersinia pseudotuberculosis
Open this publication in new window or tab >>The Twin Arginine Translocation System is Essential for Virulence of Yersinia pseudotuberculosis
2006 (English)In: Infection and Immunity, ISSN 0019-9567, Vol. 74, no 3, 1768-1776 p.Article in journal (Refereed) Published
Abstract [en]

Yersinia species pathogenic to humans have been extensively characterized with respect to type III secretion and its essential role in virulence. This study concerns the twin arginine translocation (Tat) pathway utilized by gram-negative bacteria to secrete folded proteins across the bacterial inner membrane into the periplasmic compartment. We have shown that the Yersinia Tat system is functional and required for motility and contributes to acid resistance. A Yersinia pseudotuberculosis mutant strain with a disrupted Tat system (tatC) was, however, not affected in in vitro growth or more susceptible to high osmolarity, oxidative stress, or high temperature, nor was it impaired in type III secretion. Interestingly, the tatC mutant was severely attenuated via both the oral and intraperitoneal routes in the systemic mouse infection model and highly impaired in colonization of lymphoid organs like Peyer's patches and the spleen. Our work highlights that Tat secretion plays a key role in the virulence of Y. pseudotuberculosis.

Identifiers
urn:nbn:se:umu:diva-4775 (URN)10.1128/IAI.74.3.1768-1776.2006 (DOI)16495550 (PubMedID)
Available from: 2005-10-27 Created: 2005-10-27Bibliographically approved
2. YscP and YscU Regulate Substrate Specificity of the Yersinia Type III Secretion System
Open this publication in new window or tab >>YscP and YscU Regulate Substrate Specificity of the Yersinia Type III Secretion System
Show others...
2003 (English)In: Journal of Bacteriology, ISSN 0021-9193, Vol. 185, no 7, 2259-2266 p.Article in journal (Refereed) Published
Abstract [en]

Pathogenic Yersinia species use a type III secretion system to inhibit phagocytosis by eukaryotic cells. At 37 degrees C, the secretion system is assembled, forming a needle-like structure on the bacterial cell surface. Upon eukaryotic cell contact, six effector proteins, called Yops, are translocated into the eukaryotic cell cytosol. Here, we show that a yscP mutant exports an increased amount of the needle component YscF to the bacterial cell surface but is unable to efficiently secrete effector Yops. Mutations in the cytoplasmic domain of the inner membrane protein YscU suppress the yscP phenotype by reducing the level of YscF secretion and increasing the level of Yop secretion. These results suggest that YscP and YscU coordinately regulate the substrate specificity of the Yersinia type III secretion system. Furthermore, we show that YscP and YscU act upstream of the cell contact sensor YopN as well as the inner gatekeeper LcrG in the pathway of substrate export regulation. These results further strengthen the strong evolutionary link between flagellar biosynthesis and type III synthesis.

Identifiers
urn:nbn:se:umu:diva-4776 (URN)10.1128/JB.185.7.2259-2266.2003 (DOI)
Available from: 2005-10-27 Created: 2005-10-27Bibliographically approved
3. Proteolytic Cleavage of the FlhB Homologue YscU of Yersinia pseudotuberculosis Is Essential for Bacterial Survival
Open this publication in new window or tab >>Proteolytic Cleavage of the FlhB Homologue YscU of Yersinia pseudotuberculosis Is Essential for Bacterial Survival
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2002 (English)In: Journal of Bacteriology, ISSN 0021-9193, Vol. 184, no 16, 4500-4509 p.Article in journal (Refereed) Published
Abstract [en]

Pathogenic Yersinia species employ a type III secretion system (TTSS) to target antihost factors, Yop proteins, into eukaryotic cells. The secretion machinery is constituted of ca. 20 Ysc proteins, nine of which show significant homology to components of the flagellar TTSS. A key event in flagellar assembly is the switch from secreting-assembling hook substrates to filament substrates, a switch regulated by FlhB and FliK. The focus of this study is the FlhB homologue YscU, a bacterial inner membrane protein with a large cytoplasmic C-terminal domain. Our results demonstrate that low levels of YscU were required for functional Yop secretion, whereas higher levels of YscU lowered both Yop secretion and expression. Like FlhB, YscU was cleaved into a 30-kDa N-terminal and a 10-kDa C-terminal part. Expression of the latter in a wild-type strain resulted in elevated Yop secretion. The site of cleavage was at a proline residue, within the strictly conserved amino acid sequence NPTH. A YscU protein with an in-frame deletion of NPTH was cleaved at a different position and was nonfunctional with respect to Yop secretion. Variants of YscU with single substitutions in the conserved NPTH sequence--i.e., N263A, P264A, or T265A--were not cleaved but retained function in Yop secretion. Elevated expression of these YscU variants did, however, result in severe growth inhibition. From this we conclude that YscU cleavage is not a prerequisite for Yop secretion but is rather required to maintain a nontoxic fold.

Identifiers
urn:nbn:se:umu:diva-4777 (URN)10.1128/JB.184.16.4500-4509.2002 (DOI)12142420 (PubMedID)
Available from: 2005-10-27 Created: 2005-10-27Bibliographically approved

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