PhoP-PhoQ: Difference between revisions

E. coli phoP is a 223 residue protein containing a 120-residue regulatory domain joined by a 5-residue linker to a 98 residue c-terminal DNA binding effector domain.<ref name=Bachhawat>PMID:17545283</ref> At a conserved Asp residue (<scene name='PhoP-PhoQ/Asp51-bef3/1'>Asp51 in this case</scene>), the regulatory domain can be modified by a phosphoryl group from the protein kinase function of phoQ. Phosphorylation of the regulatory domain modulates the activity of the effector domain to bind DNA and regulate transcription. Phosphorylated, or "activated" phoP binds to "phoP boxes" on bacterial DNA, which consist of two direct hexanucleotide repeats separated by a five nucleotide spacer located at the -35 position.<ref name=Bachhawat>PMID:17545283</ref>:

Spontaneous dimerization of the unactivated phoP regulatory domain can be observed in vitro, but is likely due to high concentration of the protein and may not occur in vivo. Although the dimerization of the unactivated phoP regulatory domain results in a homodimer similar to the activated homodimer, it is significantly less stable. Activation by the phosphoryl group helps to stabilize the <scene name='Sandbox_Reserved_344/Dimerization_surface/1'>α-4 helix, β-5 sheet and α-5 helix face</scene> dimerization interphase. Without the phosphoryl group, the two monomers dimerize in an asymmetric fashion that lends to molecular instability.