PS3

Seeing the light of Solar Energy Conversion Photosynthesis is essential to life on earth, now researchers in the PS3 project are drawing inspiration from the process to develop a solar energy conversion system. We spoke to Dr Dror Noy about the project’s work in designing protein cofactor complexes with photosystem functionality, which could point the way towards new bioreactors for fuel production.

The process of photosynthesis is responsible for the energy sources that we all rely on in our daily lives, enabling the conversion of light energy into chemical energy. Photosynthesis is the best characterised and understood of all the biological processes, on the molecular level, as it can be easily triggered with light. “Because photosynthesis is a lightdependent process, the molecules that are doing the work have colour. When they do their work they change their colour, which can be monitored,” explains Dr Dror Noy. Based at the Migal Galilee Research Institute in Israel, Dr Noy is the Principal Investigator of the PS3 project, an initiative which aims to develop a light energy conversion system, drawing inspiration from the initial part of the photosynthesis process in natural systems. “We focus on the first, preliminary steps in photosynthesis in the PS3 project – these are the absorption of light, and the conversion of this light into useful chemical potential,” he outlines.

A lot of information is available about this part of the process, including information relating to the molecular structure, geometry and organisation of photosynthetic complexes. These complexes make up a significant proportion of the cell membranes of photosynthetic organisms, giving researchers solid foundations on which to investigate photosynthesis. “Since plenty of biological samples are available, www.euresearcher.com

we can run all kinds of biochemical and structural characterisations,” says Dr Noy. The structure and properties of these complexes have been well characterised, now Dr Noy and his colleagues in the project aim to implement what they’ve learned in the development of a new light energy conversion system. “Given what we know about photosynthesis, about how it is carried out in biology, we now aim to generate our own protein-pigment complexes, that will perform similar functions,” he says.

of artificial complexes,” he continues.

“Proteins are polymers of amino-acids.

Their three-dimensional structure, and most importantly their functionality derived from this structure, is actually determined by how the amino-acids are ordered within this polymer chain.”

The key challenge here is to come up with the sequences of amino-acids that will lead to the right structure, which in turn will give researchers the desired functionality. This is a very complex, technically demanding

One major difference with biological systems relates to the membrane, a set of structures of lipids, which are very hydrophobic, the properties of this membrane are very different to those of water. It is where the natural system is assembled and located.

Light energy conversion This is a technically challenging task, with researchers looking to produce a fully functional light energy conversion system, built on a detailed understanding of the underlying processes involved in energy and electron transfer. Within the project, a key part of the role of Dr Noy and his group is to make new proteins, based on the rules of how proteins are created. “In my group we specialise in photosynthetic complexes, but also in protein design and the preparation

problem. “There are 20 different naturally occurring amino-acids, and a protein chain is typically a sequence of a dozen to a few hundreds of them connected in a row, so there are an enormous number of potential combinations. We’re trying to get this protein structure right, with the right sequence of amino-acids,” says Dr Noy. The project also includes a group of computational chemists led by Professor Vikas Nanda, based at Rutgers University in the US, whose expertise helps in identifying the

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The design of a novel minimal photosystem is the main goal of the PS3 project. For this, the natural photosystems are the source of inspiration. All photosynthetic organisms use only two types of photosystems, namely the type II quinone, or type I iron-sulfur reducing photosystems. Anoxygenic photosynthetic bacteria use either a type I, or a type II photosystem, whereas cyanobacteria, algae, and plants combine both types into a photosynthetic apparatus capable of water reduction and oxygen evolution. All photosystems reside in the membranes and are coupled to proton pumps for driving ATP synthesis. By using computational protein design tools a novel protein pigment complexes are designed and constructed.

These are combined to form PS3, a water-soluble protein-pigment complex that captures the essence of photosystem functionality – light driven electron transport from external electron donors to electron acceptors.

right sequences of amino-acids. “Professor Nanda’s group are experts in computational protein design. We use computational algorithms to come up with the sequences we need in order to make our complexes.

We code these protein sequences into DNA, then these codes are introduced into E. coli bacteria to drive production of the desired protein,” outlines Dr Noy. This provides researchers with a protein, but this is just the first step.

An extra challenge when dealing with photosynthetic complexes is that you also need to assemble the proteins with the components that actually do the photochemistry. “Some components absorb and emit light – so they transport energy - and some components make charge separation – so they transport electrons. By these two actions, namely energy and electron transport, light is eventualy converted into electric potential,” explains Dr Noy. Plants use chlorophyll molecules for both actions; what determines the specific role of each chlorophyll is its relative position with respect to other pigments and the nearby protein environment that tunes

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its properties. Researchers aim to develop protein-cofactor complexes to perform in a similar way, inspired by photosynthesis but not necessarily replicating it in every respect. “We aim to develop a module that can do very much the same work,” says Dr Noy. “One major difference with biological systems relates to the membrane,

The key in PS3 however is to take the system out of the membrane, as the interest here is not ATP, but rather a different energy storage molecule.

“Actually generating this molecule is beyond the scope of this project, but if we can generate an electro-chemical driving force, that we can interface with enzymes

Proteins are polymers of amino-acids. Their three-dimensional structure, and most importantly their functionality derived from this structure, is actually determined by how the amino-acids are ordered within this polymer chain. a set of structures of lipids, which are very hydrophobic, the properties of this membrane are very different to those of water. It is where the natural system is assembled and located,” explains Dr Noy. The reason that everything is in a membrane is because in the biological system the membrane is required to generate adenosine triphosphate (ATP), a transient molecule for the storage of energy.

that can do very efficient biochemistry, then that could help us generate energyrich molecules for example,” says Dr Noy. The concept is relatively simple, and Dr Noy says it holds clear potential in terms of fuel production. “In a typical system, we will effectively shine light on proteins in solution. In the same test tube we will also have an enzyme that will use some of the transferred electrons to do its redox

EU Research

PS3 An artificial water-soluble photosystem by protein design

Project Objectives

The PS3 project aims at producing a fully functional light energy conversion system that is inspired by, but does not necessarily mimic, the fundamental solar energy conversion unit of natural photosynthesis – the photosystem. This formidable challenge is addressed by implementing our thorough understanding of biological energy and electron transfer processes, and the growing capabilities of computational protein design.

Project Funding

The PS3 project is funded by an consolidator grant from the ERC

Project Partners

• Migal – Galilee Research Institute, Israel • The Center for Advanced Biotechnology and Medicine (CABM), Rutgers University, USA

Contact Details

Design of a water-soluble chlorophyll-binding protein analogous to natural light harvesting complexes. The design is based on a conserved structural motif found in PSI and PSII. The natural motif is a transmembranal protein, thus it has a mostly hydrophobic surface (shown in pink). Computational protein design converted the outer surface into a hydrophilic surface (shown in turquoise).

chemistry,” he explains. “In this way we can use highly sophisticated catalytic sites of the enzymes, and generate molecules that can be used as fuel.”

A prime example is the very potent enzymes that can reduce the protons in water to make hydrogen.

If hydrogen production can be coupled to the generation of electric potential through harnessing solar energy, that could provide a means of storing energy. “These processes may be the target of the photosystems produced in the PS3 project,” says Dr Noy. This research could hold important implications for future energy provision, opening up new possibilities in solar energy conversion and light-driven fuel production.

“If you can make these proteins, possibly by using certain kinds of genetic engineering methods, then we can think about a hybrid system, a system that uses both biological and synthetic material. This could mean some kind of bioreactor, a means to generate some useful fuel,” outlines Dr Noy. “That is a long way beyond the scope of the PS3 project however, and there are many challenges to deal with first, including

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ensuring that the protein complexes are stable enough to last.”

The main practical challenge for Dr Noy and his colleagues in terms of the project’s goals at this point is working out how to control the assembly of these proteinpigment complexes, and while a lot of progress has been made in the field of protein design, there is still more to learn.

The task is complicated further by the need to introduce the pigments into the proteins.

“This is like drug design in reverse. Instead of building a molecule to fit into a protein binding site, you build a binding site to fit a molecule,” says Dr Noy. An additional challenge is that the pigments themselves are not necessarily soluble in water, as they come from the photosynthetic membranes.

“So we need to figure out ways to make sure that these pigments are soluble in water,” continues Dr Noy. “These are the kinds of challenges that we deal with on a daily basis.

We are learning a lot of new techniques and methods that can help us build new functional proteins, not only with respect to this project, but also others that we are involved with.”

Project Coordinator, Dr Dror Noy Bioenergetics and Protein Design laboratory MIGAL - Galilee Research Institute MIGAL Building, Southern Industrial Zone, Tarshish st.

Kiryat Shmona P.O.B. 831 Kiryat Shmona 11016 Israel T: +972-4-7700508 E: drorn@migal.org.il W: http://www.migal.org.il/Dror-NoyBioenergetics-and-Protein-Design-laboratory Dr Dror Noy

Dr Dror Noy is currently the head of the biotechnology department and the laboratory for bioenergetics and protein design at Migal-Galilee Research Institute.

In 2000, after obtaining his PhD in chemistry from the Weizmann Institute of Science, he was a post-doctoral fellow in the University of Pennsylvania. From 2007, he was a research group leader at the Plant Science department at the Weizmann Institute, and moved to his current position at Migal in 2013.

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