The voltage output part of our project aims to mimic the signal transduction that occurs at a neural synapse. We are engineering E.coli to create a voltage output on detection of glutamate. This imitates the creation of a postsynaptic potential in a dendrite when a neurotransmitter (such as glutamate) is present at the synapse.
The mechanism we have designed is similar to that used in the brain – relying on ion movement across the membrane, and gated ion channels. To simplify the concept, we are only regulating and measuring the flux of potassium (K+) ions, and we are using a directly glutamate-gated K+ ion channel. This means that on the binding of glutamate, the channels will open, allowing a K+ flux, which will change the voltage of the medium enough to be detected with a very sensitive electrode.
In order to set up a large enough K+ concentration gradient across the membrane for ions to flow down when the channels open, an ion pump is necessary. E.coli has a transmembrane P-type ATPase called Kdp, which pumps K+ into the cell. We have isolated this gene to overexpress it, therefore causing the cells to pump in a large number of K+ ions.
However, E.coli also has a number of osmoregulatory systems which use relative K+ ion concentrations to control turgor. There are K+ leak channels (Kch and Kef) in the membrane, so we have ordered E.coli strains with mutations in these genes to allow K+ to remain sequestered inside the cells until the glutamate-gated channels open.
Mutant Strains Information
Flame Photometer Calibration
OD600 (Cell Density) Calibration
Mutant Growth Rates
Induced Cytoplasmic K+ Concentrations
Protein prediction tools
Kdp operon diagram
The Kdp-ATPase system and its regulation
Potential Chassis: |Strain JW1242-1
Kdp mutant - paper from 1971
Worldwide E.coli Databases
Characterisation of kdpD - 2005
Investigations on Kdp Operon exp. & flux
Very interesting 2001 paper concerning Glutamate Channels
1999 paper on functional characterization of prokaryote Glu Channels
Sequenced Synechocystis PCC 6803 genome
Glutamate-gated K+ channel GluR0
Link to E.coli statistics page (CCDB Database)