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
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
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DOI：
10.1128/jb.185.16.4825-4836.2003
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发表时间：
2003-08-01
影响因子：
3.2
通讯作者：
Skorupski, K
中科院分区：
文献类型：
--
作者：
Kovacikova, G;Lin, W;Skorupski, K
AphA和AphB激活弧菌致病性岛上的tcpPH启动子，启动霍乱弧菌毒力级联，并通过HapR对AphA表达的抑制作用通过群体感应调节。为了进一步了解染色体编码的AphA蛋白是如何激活tcpPH表达的，研究人员使用定点诱变技术来鉴定对AphA结合和转录激活至关重要的碱基对。这一分析揭示了部分双对称区域TATGCA-N6-TNCNNA对这两种活性都很重要。在霍乱病毒基因组中寻找这个结合位点，可以在小染色体上的青霉素V氨基酶（PVA）基因上游发现第二个结合位点。AphA结合并足迹于该位点，该位点与pva转录起始位点重叠，与其在该启动子处作为抑制因子的作用一致。由于aphA的表达受群体感应控制，反应调节因子LuxO和HapR也会影响pva的表达。因此，当AphA水平高时，pva在低细胞密度下被抑制，而当AphA水平降低时，pva在高细胞密度下被抑制。青霉素酰胺酶被认为是非寄生环境中苯乙酰化化合物的清道夫。AphA对pva的表达与毒力的表达具有相反的调节作用，而pva在毒力中不起作用，这表明这些活动是协调一致的，可以在不同的生物生态位中为霍乱弧菌服务。
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.