Four VirB6 Paralogs and VirB9 Are Expressed and Interact in Ehrlichia chaffeensis-Containing Vacuoles

ABSTRACT The type IV secretion system is an important virulence factor in several host cell-associated pathogens, as it delivers various bacterial macromolecules to target eukaryotic cells. Genes homologous to several virB genes and virD4 of Agrobacterium tumefaciens are found in an intravacuolar pathogen Ehrlichia chaffeensis, the tick-borne causative agent of human monocytic ehrlichiosis. In particular, despite its small genome size, E. chaffeensis has four tandem virB6 paralogs (virB6-1, -2, -3, and -4) that are 3- to 10-fold larger than A. tumefaciens virB6. The present study for the first time illustrates the relevance of the larger quadruple VirB6 paralogs by demonstrating the protein expression and interaction in E. chaffeensis. All four virB6 paralogs were cotranscribed in THP-1 human leukemia and ISE6 tick cell cultures. The four VirB6 proteins and VirB9 were expressed by E. chaffeensis in THP-1 cells, and amounts of these five proteins were similar in isolated E. chaffeensis-containing vacuoles and vacuole-free E. chaffeensis. In addition, an 80-kDa fragment of VirB6-2 was detected, which was strikingly more prevalent in E. chaffeensis-containing vacuoles than in vacuole-free E. chaffeensis. Coimmunoprecipitation analysis revealed VirB9 interaction with VirB6-1 and VirB6-2; VirB6-4 interaction with VirB6-1, VirB6-2, and VirB6-3; and VirB6-2 80-kDa fragment interaction with VirB6-3 and VirB6-4. The interaction of VirB9 and VirB6-2 was confirmed by far-Western blotting. The results suggest that E. chaffeensis VirB9, the quadruple VirB6 proteins, and the VirB6-2 80-kDa fragment form a unique molecular subassembly to cooperate in type IV secretion.

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Agrobacterium-Mediated T-DNA Transfer and Integration by Minimal VirD2 Consisting of the Relaxase Domain and a Type IV Secretion System Translocation Signal

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-22-11-1356 ◽

2009 ◽

Vol 22 (11) ◽

pp. 1356-1365 ◽

Cited By ~ 28

Author(s):

Maartje van Kregten ◽

Beatrice I. Lindhout ◽

Paul J. J. Hooykaas ◽

Bert J. van der Zaal

Keyword(s):

Secretion System ◽

Type Iv Secretion ◽

Type Iv Secretion System ◽

Terminal Part ◽

Type Iv ◽

C Terminus ◽

Localization Signal ◽

Translocation Domain ◽

First Time

The VirD2 protein of Agrobacterium tumefaciens is essential for processing and transport of the T-DNA. It has at least three functional domains: a relaxase domain at the N terminus, a bipartite nuclear localization signal (NLS), and a sequence called ω at the C terminus. We confirm here that deletions of the C-terminal part of VirD2 led to lack of transfer of T-DNA but, for the first time, we report that virulence is restored when these truncations are supplemented at the C terminus by a short translocation signal from the VirF protein. The lack of virulence of C-terminal deletions suggests that the C-terminal part contains all or part of the translocation signal of VirD2. Using a novel series of mutant VirD2 proteins, the C-terminal half of VirD2 was further investigated. We demonstrate that the C-terminal 40 amino acids of VirD2, which include the NLS and ω, contain all or part of the translocation domain necessary for transport of VirD2 into plant cells, while another element is present in the middle of the protein. The finding that a type IV secretion system transport signal at the C terminus of VirD2 is necessary for virulence provides evidence for the role of VirD2 as a pilot protein driving translocation of the T-strand.

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Type IV Secretion System of Anaplasma phagocytophilum and Ehrlichia chaffeensis

Annals of the New York Academy of Sciences ◽

10.1111/j.1749-6632.2009.04527.x ◽

2009 ◽

Vol 1166 (1) ◽

pp. 106-111 ◽

Cited By ~ 13

Author(s):

Yasuko Rikihisa ◽

Mingqun Lin ◽

Hua Niu ◽

Zhihui Cheng

Keyword(s):

Anaplasma Phagocytophilum ◽

Secretion System ◽

Type Iv Secretion ◽

Type Iv Secretion System ◽

Ehrlichia Chaffeensis ◽

Type Iv

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The VirB System Plays a Crucial Role in Brucella Intracellular Infection

International Journal of Molecular Sciences ◽

10.3390/ijms222413637 ◽

2021 ◽

Vol 22 (24) ◽

pp. 13637

Author(s):

Xue Xiong ◽

Bowen Li ◽

Zhixiong Zhou ◽

Guojing Gu ◽

Mengjuan Li ◽

...

Keyword(s):

Secretion System ◽

Type Iv Secretion ◽

Host Cells ◽

Type Iv Secretion System ◽

Vaccine Research ◽

Gram Negative ◽

Type Iv ◽

New Ideas ◽

Important Virulence Factor ◽

Cellular Pathways

Brucellosis is a highly prevalent zoonotic disease caused by Brucella. Brucella spp. are gram-negative facultative intracellular parasitic bacteria. Its intracellular survival and replication depend on a functional virB system, an operon encoded by VirB1–VirB12. Type IV secretion system (T4SS) encoded by the virB operon is an important virulence factor of Brucella. It can subvert cellular pathway and induce host immune response by secreting effectors, which promotes Brucella replication in host cells and induce persistent infection. Therefore, this paper summarizes the function and significance of the VirB system, focusing on the structure of the VirB system where VirB T4SS mediates biogenesis of the endoplasmic reticulum (ER)-derived replicative Brucella-containing vacuole (rBCV), the effectors of T4SS and the cellular pathways it subverts, which will help better understand the pathogenic mechanism of Brucella and provide new ideas for clinical vaccine research and development.

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