Team:Pretoria UP/Description
What is WattsAptamer?
Just like WhatsApp® is connecting many problem solvers without vast expenses, our project concept connects the electron generator of plants (photosystems in thylakoid membranes) to a carbon-based electrode with short DNA strandslinkers called aptamers. This connection generates clean electricity which can potentially solve the increasing demand for carbon-neutral power!
WattsAptamer Project Design.
References
Fossil fuel levels are depleting and we need to find alternative and green energy sources. We have found a potential solution! Recently, scientists attached light-absorbing photosystems found in plant chloroplasts to superconductive graphene electrodes. When sunlight shines on the thylakoid membrane in which the photosystems are housed, free electrons are generated which can be harvested to generate electricity. In order to bind the thylakoid membrane, we have engineered sequences of short DNA strands, called aptamers. One end of the aptamer binds specifically to the electron producing protein in the thylakoid membrane and the other side to the graphene plate. Optimal electron harvest is aided by the aptamers, which bind the photosystem proteins in the correct orientation. This ensures a higher yield of electrons traveling to the graphene anode. Laccase proteins are attached to the cathode which acts as an electron acceptor. This creates a potential difference which leads to electricity being generated by plants!
Our goal for the WattsAptamer project is to provide a clean, inexpensive power generation alternative to current fossil fuel based approaches, by means of photo-bioelectrochemical cells (PBECs). Simply put, we are engineering a plant based battery!
The idea to make these “plant batteries” stems from our very own struggles in South Africa where we are faced with an electricity crisis. The South African population is adapting to live in the dark, as our national power utility is unable to meet electricity demand and as a result they have to keep implementing a tortuous schedule of rolling blackouts known as “load shedding”. It has advanced to such a state that South Africans now check electricity reports that read like weather forecasts.
The problem however is not limited to South Africa but extends to the world. There are many countries in the world where the greater proportion of the population does not have access to electricity. Additionally, the world population consumes approximately 3500 kWh/y/capita. To put this into perspective, this figure is equivalent to approximately 11 nuclear bombs exploding each year. Not only does the burning of fossil fuels create sizeable amounts of pollution, it is also finite and will eventually run out.
As the University of Pretoria iGEM team, we decided to take it upon ourselves to make a difference by using a synthetic biology approach to combating the electricity problems we are challenged with as a nation as well as on a global scale, by building our WattsAptamer “battery”.
When designing WattsAptamer, we as a multidisciplinary team of biologists and engineers combined our knowledge of our respective fields and constructed our design. The biologists in the group knew all about how nature generates energy through photosynthesis, and as such came up with the idea to attach thylakoids to an electrode. In the presence of light these thylakoids will split water into hydrogen and oxygen, and this charge separation step releases free electrons. The engineers then opened our eyes to the world of graphene. Graphene is made from graphite and has the most amazing physical properties, one of which is that it is a superconductive material. To give you an idea of just how conductive “superconductive” is: graphene is 1000 times more conductive than copper. And that’s only one of its phenomenal properties. The engineers suggested that we use graphene as the electrodes in our system.
We then developed our design further and chose to attach the thylakoid proteins to the graphene cathode using aptamers. Aptamers are single stranded DNA or RNA oligo’s that form secondary structures that can specifically bind to a target site. Our aptamer consists of 3 parts, the first part will be designed to bind to a specific part of a protein embedded in the PSII protein complex known as CP47. The second part of the aptamer will serve as a linker between part one and part three. The third part of the aptamer will be selected using SELEX to specifically bind to graphene foam. Thus our complete aptamer will tether the thylakoid protein to the graphene foam cathode.
As mentioned before, when in the presence of light the thylakoid proteins will split water into hydrogen and oxygen, this charge separation step will generate free electrons which will then be funneled from the PSII proteins to the graphene cathode. From the cathode the electrons will move to the anode which is also made of graphene foam.
Laccases are tethered to the anode using PBSE, which is an aromatic amine compound. The laccases which are of eucalyptus origin will accept the electron from the cathode and use it to reduce the free hydrogen and oxygen back into water and as such make the cell a sustainable system.
See our results here.
Chen Ji, Zhao Lu, Bai Hua, Shi Gaoquan, 2011. Electrical detection of dioxygen and hydrogen peroxide by hemin immobilised on chemical converted graphene. Journal of Electroanalytical Chemistry 657(1-2): 34-38 .
Germer, K., Leonard, M. and Zhang, X., 2013. RNA aptamers and their therapeutic and diagnostic applications. International Journal of Biochemistry and Molecular Biology 4(1), 27-40.
Ramasamy Ramaraja P., Luckarift Heather R., Ivnitski Dimitri M., Atanassov Plamen B. and Johnson Glenn R., 2010. High electrocatalytic activity of tethered multicopper oxidase-carbon nanotube conjugates. Chemical Communications 46: 6045-6047.
Sekar, N. Ramasamy, R. P. 2015. Photosynthetic energy conversion : recent advances and future perspective. The Electrochemical Society Interface, viewed 18 February 2016, www.electrochem.com.
Somepics 2015, Light-dependent reactions of photosynthesis in the thylakoid membrane of plant cells, viewed 13 September 2016, https://en.wikipedia.org/wiki/File:Thylakoid_membrane_3.svg.
Yehezkeli O, Tel-Vered R, Michaeli D, Willner I, Nechushtai R. 2014. Photosynthetic reaction center-functionalized electrodes for photo-bioelectrochemical cells. Photosynthesis Research 120: 71-85.1
