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Infection and Immunity, April 2005, p. 2433-2443, Vol. 73, No. 4
0019-9567/05/$08.00+0 doi:10.1128/IAI.73.4.2433-2443.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Center for Infectious Diseases and Department of Molecular Genetics and Microbiology,1 Department of Biochemistry and Cell Biology, State University of New York at Stony Brook, Stony Brook, New York2
Received 18 June 2004/ Returned for modification 27 July 2004/ Accepted 12 November 2004
YopB is a 401-amino-acid protein that is secreted by a plasmid-encoded type III secretion system in pathogenic Yersinia species. YopB is required for Yersinia spp. to translocate across the host plasma membrane a set of secreted effector proteins that function to counteract immune signaling responses and to induce apoptosis. YopB contains two predicted transmembrane helices (residues 166 to 188 and 228 to 250) that are thought to insert into the host plasma membrane during translocation. YopB is also required for pore formation and host-cell-signaling responses to the type III machinery, and these functions of YopB may also require membrane insertion. To elucidate the importance of membrane insertion for YopB function, YopB proteins containing helix-disrupting double consecutive proline substitutions in the center of each transmembrane domain were constructed. Yersinia pseudotuberculosis strains expressing the mutant YopB proteins were used to infect macrophages or epithelial cells. Effector translocation, pore formation, and host-cell-signaling responses were studied. Introduction of helix-disrupting substitutions into the second transmembrane domain of YopB resulted in a nonfunctional protein that was not secreted by the type III machinery. Introduction of helix-disrupting substitutions into the first transmembrane domain of YopB resulted in a protein that was fully functional for secretion and for interaction with YopD, another component of the translocation machinery. However, the YopB protein with helix-disrupting substitutions in the first transmembrane domain was partially defective for translocation, pore formation, and signaling, suggesting that all three functions of YopB involve insertion into host membrane.
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