The virulence activator AphA links quorum sensing to pathogenesis and physiology in Vibrio cholerae by repressing the expression of a penicillin amidase gene on the small chromosome.
Activation of the tcpPH promoter on the Vibrio pathogenicity island by AphA and AphB initiates the Vibrio cholerae virulence cascade and is regulated by quorum sensing through the repressive action of HapR on aphA expression. To further understand how the chromosomally encoded AphA protein activates tcpPH expression, site-directed mutagenesis was used to identify the base pairs critical for AphA binding and transcriptional activation. This analysis revealed a region of partial dyad symmetry, TATGCA-N6-TNCNNA, that is important for both of these activities. Searching the V. cholerae genome for this binding site permitted the identification of a second one upstream of a penicillin V amidase (PVA) gene on the small chromosome. AphA binds to and footprints this site, which overlaps the pva transcriptional start, consistent with its role as a repressor at this promoter. Since aphA expression is under quorum-sensing control, the response regulators LuxO and HapR also influence pva expression. Thus, pva is repressed at low cell density when AphA levels are high, and it is derepressed at high cell density when AphA levels are reduced. Penicillin amidases are thought to function as scavengers for phenylacetylated compounds in the nonparasitic environment. That AphA oppositely regulates the expression of pva from that of virulence, together with the observation that PVA does not play a role in virulence, suggests that these activities are coordinated to serve V. cholerae in different biological niches.
Kovacikova
Gabriela
G
Department of Microbiology and Immunology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Lin
Wei
W
Skorupski
Karen
K
D000619:Aminohydrolases / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D002876:Chromosomes, Bacterial; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010399:Penicillin Amidase / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014734:Vibrio cholerae / Q000201:enzymology / Q000235:genetics / Q000254:growth & development* / Q000472:pathogenicity*; D014774:Virulence; D000581:Amidohydrolases
D000619:Aminohydrolases; D001426:Bacterial Proteins; D036781:Fimbriae Proteins; D010399:Penicillin Amidase; D014157:Transcription Factors; C097244:TCPP protein, Vibrio cholerae; C099204:TcpH protein, Vibrio cholerae; C058087:acetylpolyamine amidohydrolase; D000581:Amidohydrolases