Team:UC Davis/pH Sensor/parts

From 2009.igem.org

ChvG

Acidic condition plays an important role in Agrobacterium-plant interactions (1).

Numerous studies have investigated the possible connection between the physiological response to acidic conditions and the activity of ChvG and ChvI. Studies have shown that ChvG /ChvI two component systems specifically get induced in an acidic environment (1).

As a result, there is growing consensus that the ChvG/ChvI, two-component regulatory system, may be the primary global pH sensor in Agrobacterium tumefaciens and as such, serves in coordinating the expression of acid-induced genes (2).

ChvI

ChvI is the response regulator of the ChvG/ChvI two component regulatory system found in Agrobacterium (4).

ChvG ---> ChvI

ChvG and ChvI is the sensor kinase, and cognate response regulator, respectively, of two component regulatory system in Agrobacterium thought to respond to extracellular pH changes (2).

PhoB

PhoB is a response regulator in E.coli that gets activated by a histidine kinase and phosphate sensor called PhoR (6).

PhoR

PhoR is a histidine kinase and a phosphate sensor in E. coli that activates a response regulator called PhoB (6).

PhoR-->ChvI

It has been hypothesized that due to the amino acid similarity of ChvI to PhoB, ChvI is able to act as a phosphate regulatory in E. coli, as a PhoB substitute (3).

Since ChvI showed no abnormal activity inside Agrobacterium tumefaciens under phosphate limitation, it cannot serve as the primary phosphate regulator in Agrobacterium (3).

Note: ChvI was not required for phosphate regulation in Agrobacterium Tumefaciens (3), but it might be involved in phosphate regulation in Agrobacterium tumefaciens in some way (3). Therefore, the possibility of crosstalk still exists.

Due to the structural similarity of ChvI and PhoB, the possibility of crosstalk exists (3).

Note: Since we are going to use Escherichia coli as our model chassis for this project; we had to make sure that our proteins will keep their characteristics of our interest after being placed inside the Escherichia coli. For example, VirG gene (promoter 1) after being introduced into E.coli cells, started to behave as if it were a member of phosphate regulation (note: PhoB function was necessary for virG induction by phosphate starvation)(6). Studies have suggested that the reason for this behavior was due to the fact that virG promoter 1 has two hexamer blocks which have the same positions as the pho genes (6).

Studies have shown that ChvI probably activated Alkaline Phosphatase (AP) activity by activating transcription of PhoA (PhoA also gets activated by PhoB) (3). It was not proven that ChvI activates other PhoB-dependent promoters or recognizes the same DNA sequence as PhoB (3).But, there has been speculation that since PhoR mediates PhoB phosphorylation and dephosphorylation, it may do the same to ChvI(3).

Therefore, the best option would be to find a promoter from Agrobacterium that gets activated by ChvG/ChvI, a two-component regulatory system only; and does not interact with any E. coli system.

PhoR-->PhoB

In E. coli, the PhoR/PhoB two component system senses phosphate levels to activate genes that mediate phosphate starvation (3).