Team:Hong Kong-CUHK/Project future

Future

What we show in our project is only the tip of the whole iceberg. More possible applications of halorhodopin could benefit not only synthetic biology but also the human society. Here we propose several more advanced applications of halorhodopsin.

Halorhodopsin could facilitate light detection and light-coupled inter-cell signal transduction. Light signal could be converted to intracellular chloride level signal, which thus induces Pgad downstream genes. The target genes could be constructed to accelerate the synthesis 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 and converting light signal to quorum signal to cooperate with other clones of bacteria.

Moreover, halorhodopsin is not the only channel that couples light to pump ions. There are other ion channels from retinylidene protein family sharing similar sequences and structures but pumping other ions using light, such as bacteriorhodopsin pumping proton ions out of cells2 and channelrhodopsin non-specifically pumping cations into cells3. Combining pH sensitive promoter4 with bacteriorhodopsin and osmolality sensitive promoters (OmpF, developed by iGEM08_NYMU-Taipei in 2008) with channelrhodopsin, the light-coupled expression platform can be extended to more accurate and more complex regulation, which facilitates bacteria being more programmable by computer.

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

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

References

• Shapiro, J. a Thinking about bacterial populations as multicellular organisms. Annual review of microbiology 52, 81-104(1998).
• Hayashi, S., Tajkhorshid, E. & Schulten, K. Molecular dynamics simulation of bacteriorhodopsin’s photoisomerization using ab initio forces for the excited chromophore. Biophysical journal 85, 1440-9(2003).
• Nagel, G. et al. Channelrhodopsin-2, a directly light-gated cation-selective membrane channel. Proceedings of the National Academy of Sciences 100, 13940(2003).
• San, K. et al. An Optimization Study of a pH-Inducible Promoter System for High-Level Recombinant Protein Production in Escherichia coli. Annals of the New York Academy of Sciences 721, 268–276(1994).