Team:Macquarie Australia/Project/Significance

Potential pathway for Hydrogen Production

Chlorophyll biosynthesis is the first step towards creating Photosystem II (PS II). PS II is the key molecular complex in the photosynthetic pathway utilizing harvested energy from the sun to convert water into hydrogen ions, oxygen and electrons (Michel and Deisenhofer, 1988). PSII is composed of approximately 20 subunits that use chlorophyll molecules as an antenna to collect photons from sunlight and funnel them into PSII (Loll et al, 2005). Thus, a future addition to our current study of synthesising chlorophyll would be to create PSII (using the same synthetic biology techniques) and then use these two compounds to split water molecules using photons to harvest hydrogen ions. If connected to a hydrogenase enzyme, this ultimately can lead to the production of hydrogen biofuel from E.coli. Creating the entire Photosystem I (PS I) as an electron harvesting complex will also add to the efficiency of the process.

Current approaches in which hydrogenases are coupled with existing photosynthesis machinery of green algae have limited efficacy due to complications involved in inserting efficient hydrogenase systems alongside existing photosystems (Lee et al. 2010). However, if synthetic biology approaches are successful, this could lead to designing more efficient and hydrogenase compatible photosystems via protein engineering(Eckenhoff and Eisenberg, 2012). Synthetically engineering a chlorophyll biosynthesis pathway is only the first step, but definitely has the potential to lead to greater innovations in future.

Figure 1. Schematic diagram of hydrogen production driven by photosystems Hydrogen production avenues connected to oxygenic photosynthesis and fueled by sunlight (yellow arrows) that is absorbed by the photosystems and transferred to the reaction center (RC). The complex is indicated in red if the pathway is a potential future avenue of BioH₂ production, such as electron transfer to hydrogenase from pheophytin (Pheo) in PS II or from the electron acceptor side of the PS I complex. Figure adapted from Lee et al. (2010).

References

• Eckenhoff, W. T. and R. Eisenberg (2012). "Molecular systems for light driven hydrogen production." Dalton Trans 41(42): 13004-13021.
• Lee, H. S., W. F. Vermaas and B. E. Rittmann (2010). "Biological hydrogen production: prospects and challenges." Trends Biotechnol 28(5): 262-271.
• Loll. B, Kern. J, Saenger. W, Zouni. A, Biesiadka, J. (2005). Towards complete cofactor arrangement in the 3.0 Å resolution structure of photosystem II. Nature, 438(7070): 1040–4.
• Michel, H., and Deisenhofer, J. (1988). “Relevance of the photosynthetic reaction center from purple bacteria to the structure of photosystem II.” Biochemistry,27(1): 1-7.