Perego M, Glaser P, Hoch J A
Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, California 92037, USA.
Mol Microbiol. 1996 Mar;19(6):1151-7. doi: 10.1111/j.1365-2958.1996.tb02460.x.
Bacteria use two-component signal transduction systems to sense and respond to their environment. A sensor kinase and a response-regulator transcription factor work in concert by phosphorylation/dephosphorylation through kinase and phosphatase activities to maintain a level of phosphorylated response regulator commensurate with the level of signal input. Signal input can be accommodated through stimulation of the kinase activity or the phosphatase activity of the two-component system. With some notable exceptions, the sensor kinases recognize a single stimulatory ligand. A new dimension in the regulation of two-component signal transduction systems was discovered in the Rap phosphatases which dephosphorylate the SpoOF response-regulator of Bacillus subtilis independent of the sensor kinases. This family of phosphatases is encoded by at least six chromosomal genes. Although not all of the phosphatases of the family have activity on phosphorylated SpoOF, the two best-characterized members, RapA and RapB, prevent sporulation by dephosphorylating this response regulator component of the phosphorelay. Phosphatase activity of RapA is regulated by a gene, phrA, in the same transcriptional unit, that encodes a peptide secreted from the cell which may serve as a quorum sensor. Most of the Rap phosphatase operons have a gene coding for a protein with some similarity to PhrA in their transcription units, but it is uncertain whether all of these play a role in regulation. The Rap phosphatases are postulated to be a mechanism for allowing signals other than those that affect the sensor kinases to regulate the signal transduction pathway. They may have been recruited to help regulate sporulation because the multiple signals regulating this process may outstrip the recognition capacity of the kinases.
细菌利用双组分信号转导系统来感知并响应其周围环境。一个传感激酶和一个反应调节转录因子协同工作，通过激酶和磷酸酶活性进行磷酸化/去磷酸化，以维持磷酸化反应调节因子的水平与信号输入水平相匹配。信号输入可以通过刺激双组分系统的激酶活性或磷酸酶活性来实现。除了一些显著的例外情况，传感激酶识别单一的刺激配体。在Rap磷酸酶中发现了双组分信号转导系统调控的一个新维度，这些磷酸酶可使枯草芽孢杆菌的SpoOF反应调节因子去磷酸化，且不依赖于传感激酶。这个磷酸酶家族由至少六个染色体基因编码。虽然该家族并非所有磷酸酶都对磷酸化的SpoOF有活性，但两个特征最明确的成员RapA和RapB，通过使磷传递中的这个反应调节因子组分去磷酸化来阻止孢子形成。RapA的磷酸酶活性由同一转录单元中的phrA基因调控，该基因编码一种从细胞分泌的肽，可能作为群体感应传感器。大多数Rap磷酸酶操纵子在其转录单元中有一个编码与PhrA有一定相似性的蛋白质的基因，但不确定所有这些基因是否都在调控中发挥作用。推测Rap磷酸酶是一种机制，用于允许除影响传感激酶的信号之外的其他信号来调节信号转导途径。它们可能已被招募来帮助调节孢子形成，因为调控这个过程的多种信号可能超出了激酶的识别能力。
