Lina G, Jarraud S, Ji G, Greenland T, Pedraza A, Etienne J, Novick R P, Vandenesch F
UPRES EA1655, Faculté de Médecine Laennec, Lyon, France.
Mol Microbiol. 1998 May;28(3):655-62. doi: 10.1046/j.1365-2958.1998.00830.x.
The agr P2 operon in Staphylococcus aureus codes for the elements of a density-sensing cassette made up of a typical two-component signalling system and its corresponding inducer. It is postulated that the autoinducer, a post-translationally modified octapeptide generated from the AgrD peptide, interacts with a receptor protein, coded by agrC, to transmit a signal via AgrA regulating expression of staphylococcal virulence genes through expression of agr RNA III. We show by analysis of PhoA fusions that AgrC is a transmembrane protein, and confirm using Western blotting that a 46 kDa protein corresponding to AgrC is present in the bacterial membrane. This protein is autophosphorylated on a histidine residue only in response to supernatants from an agr+ strain, and can also respond to the purified native octapeptide. A recombinant fusion protein where most of the N-terminal region of AgrC is replaced by the Escherichia coli maltose-binding protein is also autophosphorylated in response to stimulation by agr+ supernatants or purified octapeptide. We conclude that AgrC is the sensor molecule of a typical two-component signal system in S. aureus, and that the ligand-binding site of AgrC is probably located in the third extracellular loop of the protein.
金黄色葡萄球菌中的agr P2操纵子编码由典型的双组分信号系统及其相应诱导物组成的密度感应盒元件。据推测，自诱导物是一种从AgrD肽翻译后修饰产生的八肽，它与由agrC编码的受体蛋白相互作用，通过AgrA经由agr RNA III的表达传递信号，从而调节葡萄球菌毒力基因的表达。我们通过对PhoA融合蛋白的分析表明，AgrC是一种跨膜蛋白，并通过蛋白质印迹法确认细菌膜中存在与AgrC相对应的46 kDa蛋白。该蛋白仅在响应agr+菌株的上清液时在组氨酸残基上发生自磷酸化，并且也能对纯化的天然八肽作出反应。一种重组融合蛋白，其中AgrC的大部分N端区域被大肠杆菌麦芽糖结合蛋白取代，在受到agr+上清液或纯化八肽刺激时也会发生自磷酸化。我们得出结论，AgrC是金黄色葡萄球菌中典型双组分信号系统的传感分子，并且AgrC的配体结合位点可能位于该蛋白的第三个细胞外环中。
