Team:Hong Kong-CUHK/Project/future

• Overview
• Background
• Characterization
• Light Control
• Electricity Generation
• Future

What we show in our project is only the tip of thewhole iceberg. More possible applications of halorhodopin could benefit notonly synthetic biology but also the human society. Here we propose several moreadvanced applications of halorhodopsin.

Halorhodopsin could facilitate light detection andlight-coupled inter-cell signal transduction. Light signal could be convertedto intracellular chloride level signal, which thus induces P_gaddownstream genes. The target genes could be constructed to accelerate thesynthesis pathway of quorum sensing signals, such as N-acyl homoserine lactones(AHL)¹. As a result,one clone of bacteria could be designed as light detector, amplifying andconverting light signal to quorum signal to cooperate with other clones ofbacteria.

Moreover, halorhodopsin is not the only channel thatcouples light to pump ions. There are other ion channels from retinylideneprotein family sharing similar sequences and structures but pumping other ionsusing light, such as bacteriorhodopsin pumping proton ions out of cells² andchannelrhodopsin non-specifically pumping cations into cells³. Combining pHsensitive promoter⁴ with bacteriorhodopsinand osmolality sensitive promoters (OmpF, developed by iGEM08_NYMU-Taipei in2008) with channelrhodopsin,   the light-coupled expression platform can beextended to more accurate and more complex regulation, which facilitatesbacteria being more programmable by computer.

Together with channelrhodopsin, halorhodopsin alsoenables water desalination utilizing solar energy. Sea water desalination haslong been attractive and difficult to implement efficiently. E. coli which can express halorhodopsinand channelrhodopsin could be one promising way to solve this problem. It ispossible to drive E. coli to capturevarious ions (mainly sodium ions, potassium ions and chloride ions) in seawater and move these ions away by controlling the movement of E. coli. By this means sea water couldbe desalinated for drinking, irrigation or other daily usage.

In conclusion, halorhodopsin could fulfill the needof utilizing light as signal or energy resource. We believe that halorhodopsinwould be one of the most interesting tools of synthetic biology in the future.

References

1.        Shapiro, J. a Thinking about bacterialpopulations as multicellular organisms. Annual review of microbiology 52,81-104(1998).

2.        Hayashi, S., Tajkhorshid, E. & Schulten, K. Moleculardynamics simulation of bacteriorhodopsin’s photoisomerization using ab initioforces for the excited chromophore. Biophysical journal 85,1440-9(2003).

3.        Nagel, G. et al. Channelrhodopsin-2, a directly light-gatedcation-selective membrane channel. Proceedings of the National Academy of Sciences100, 13940(2003).

4.        San, K. et al. An Optimization Study of a pH-InduciblePromoter System for High-Level Recombinant Protein Production in Escherichiacoli. Annals of the New York Academy of Sciences 721,268–276(1994).