Locations of Mapped Genes:
Synonyms: phosphate regulatory system, PhoRB
|Superclasses:||Signal transduction pathways|
In E.coli K-12, PhoRB is the two-component system for sensing and responding to variations in the level of extracellular inorganic phosphate (Pi). Pho RB regulates the expression of a large number of genes (the Pho regulon) which have a role in the assimilation of environmental Pi or the use of alternate Pi sources.
PhoR is the membrane associated sensor kinase which controls activity of the cytoplasmic response regulator and transcription factor PhoB. PhoR detects Pi only indirectly and its activity as a sensor kinase depends on its association with the phosphate transporter PstSCAB and/or PhoU. Accordingly signal transduction by Pi requires seven proteins (PhoR, PhoB, PstSCAB and PhoU) that interact in a membrane associated complex.
PhoRB signalling is believed to be a negative process - that is, activation of PhoB is the default state and excess environmental Pi is required to turn the system off. Under limiting environmental Pi, PhoR is believed to be in an active signalling conformation resulting in the phosphorylation and activation of PhoB and subsequent induction of the Pho regulon. Excess levels of Pi (>4uM) result in an inhibited form of PhoR which interferes with phosphorylation of PhoB and prevents its activity as a transcription factor. The Pst transporter and the chaperone like protein PhoU are both necessary for inhibition of the PhoRB system.
Makino89: Makino K, Shinagawa H, Amemura M, Kawamoto T, Yamada M, Nakata A (1989). "Signal transduction in the phosphate regulon of Escherichia coli involves phosphotransfer between PhoR and PhoB proteins." J Mol Biol 1989;210(3);551-9. PMID: 2693738
Amemura90: Amemura M, Makino K, Shinagawa H, Nakata A (1990). "Cross talk to the phosphate regulon of Escherichia coli by PhoM protein: PhoM is a histidine protein kinase and catalyzes phosphorylation of PhoB and PhoM-open reading frame 2." J Bacteriol 1990;172(11);6300-7. PMID: 2228961
ArribasBosacoma07: Arribas-Bosacoma R, Kim SK, Ferrer-Orta C, Blanco AG, Pereira PJ, Gomis-Ruth FX, Wanner BL, Coll M, Sola M (2007). "The X-ray crystal structures of two constitutively active mutants of the Escherichia coli PhoB receiver domain give insights into activation." J Mol Biol 366(2);626-41. PMID: 17182055
Bachhawat05: Bachhawat P, Swapna GV, Montelione GT, Stock AM (2005). "Mechanism of activation for transcription factor PhoB suggested by different modes of dimerization in the inactive and active states." Structure 13(9);1353-63. PMID: 16154092
Blanco11: Blanco AG, Canals A, Bernues J, Sola M, Coll M (2011). "The structure of a transcription activation subcomplex reveals how σ(70) is recruited to PhoB promoters." EMBO J 30(18);3776-85. PMID: 21829166
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
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