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Infection and Immunity, October 1999, p. 5395-5408, Vol. 67, No. 10
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Virulence Role of V Antigen of Yersinia pestis at the Bacterial Surface

Kenneth A. Fields, Matthew L. Nilles,dagger Clarissa Cowan, and Susan C. Straley*

Department of Microbiology and Immunology, Chandler Medical Center, University of Kentucky, Lexington, Kentucky 40536-0084

Received 18 February 1999/Returned for modification 2 April 1999/Accepted 6 July 1999

Yersinia pestis, the etiologic agent of plague, secretes a set of environmentally regulated, plasmid pCD1-encoded virulence proteins termed Yops and V antigen (LcrV) by a type III secretion mechanism (Ysc). LcrV is a multifunctional protein that has been shown to act at the level of secretion control by binding the Ysc inner-gate protein LcrG and to modulate the host immune response by altering cytokine production. LcrV also is essential for the unidirectional targeting of Yops to the cytosol of infected eukaryotic cells. In this study, we constructed an in-frame deletion within lcrG (Delta lcrG3) to further analyze the requirement of LcrV in Yop targeting. We confirmed the essentiality of LcrV and found that LcrG may have a facilitative role, perhaps by promoting efficient secretion of LcrV. We also constructed mutants of lcrV expressing LcrV truncated at the N or C terminus. Both the N and C termini of LcrV were required for the secretion of LcrV into the medium and targeting of Yops. LcrV was detected in punctate zones on the surface of fixed Y. pestis by laser-scanning confocal microscopy, and this localization required a functional Ysc. However, the truncated LcrV proteins were not found on the bacterial surface. Finally, we tested the ability of LcrV-specific Fab antibody fragments or full-length antibody to interfere with Yop targeting and found no interference, even though this antibody protects mice against plague. These results indicate that LcrV may function in Yop targeting at the extracellular surface of yersiniae and that the protective efficacy of LcrV-specific antibodies can be manifested without blocking Yop targeting.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Chandler Medical Center, University of Kentucky, Lexington, KY 40536-0084. Phone: (606) 323-6538. Fax: (606) 257-8994. E-mail: scstra01{at}pop.uky.edu.

dagger Present address: Department of Microbiology and Immunology, University of North Dakota, Grand Forks, ND 58202.

Infection and Immunity, October 1999, p. 5395-5408, Vol. 67, No. 10
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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Copyright © 1999 by the American Society for Microbiology. All rights reserved.