Virulence role of V antigen of Yersinia pestis at the bacterial surface

Yersinia pestis, the etiologic agent of plague, secretes a set of environme ntally regulated, plasmid pCD1-encoded virulence proteins termed Yops and V antigen (LcrV) by a type III secretion mechanism (Ysc). LcrV is a multifun ctional protein that has been shown to act at the level of secretion contro l by binding the Ysc inner-gate protein LcrG and to modulate the host immun e response by altering cytokine production. LcrV also is essential for the unidirectional targeting of Yops to the cytosol of infected eukaryotic cell s. In this study, we constructed an in-frame deletion within lcrG (Delta lc rG3) to further analyze the requirement of LcrV in Yop targeting. We confir med the essentiality of LcrV and found that LcrG may have a facilitative ro le, perhaps by promoting efficient secretion of LcrV. We also constructed m utants 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 med ium and targeting of Yops. LcrV was detected in punctate zones on the surfa ce of fixed Y. pestis by laser-scanning confocal microscopy, and this local ization required a functional Ysc. However, the truncated LcrV proteins wer e not found on the bacterial surface. Finally, we tested the ability of Lcr V-specific Fab antibody fragments or full-length antibody to interfere with Yop targeting and found no interference, even though this antibody protect s mice against plague. These results indicate that LcrV may function in Yop targeting at the extracellular surface of yersiniae and that the protectiv e efficacy of LcrV-specific antibodies can be manifested without blocking Y op targeting.