Question

PhoP/PhoQ (not phosphorus uptake)

a) What does the signal detect/respond to?

b) When is the signal On/Off

c) Is the system inducible, repressible, or mixed?

d) Describe the systems response

Answer 1

a)

• In many organisms such as some Gram negative bacteria, PhoP/PhoQ regulatory signaling system exists.
• PhoP/PhoQ system act as sensors and regulate kinases to adapt them as per environmental signals, like adaptation when there is low magnesium (Mg2+) ions in the cellular environment.

• In the two domain system of PhoP/PhoQ, PhoP acts as the regulator for the response signal and PhoQ acts as the sensor to detect the environmental stimuli.

b)

• Kinases are enzymes that perform phosphorylation of proteins (enzymes).
• Phosphorylation is the predominant way for activation (on) and inactivation (off) of proteins.
• Thus, phosphorylation causes switching the system "on" and dephosphorylation causes the system to be switched "Off".

c)

• According the environmental condition, the system may be induced or repressed.
• Such as low Mg2+ ions induces the PhoP/PhoQ system, high Mg2+ will cause repression of the system.

d)

• Under certain environmental stimulation, such as lower Mg2+ ion concentration, PhoQ act as sensor and there is autophosphorylation.
• The phosphate is transferred to PhoP, this subsequenly activates to PhoP activated genes (PAG) and represses PhoP repressed genes (PRG).
• Similar observation may be observed in pH alteration.
• Similarly when conditions are reversed, PhoQ acts as phosphatase and PhoP is dephosphorylated and the conditions are also reversed.