Structural Dynamics in
Why are we interested in photosynthetic reaction centers?
Why are we interested in photosynthetic reaction centers?
All photosynthetic reaction centers have the unique capability of absorbing light and converting it into chemical energy. After the light excitation of two parallel oriented chlorophyll molecules (the so-called Special Pair) an internal electron transfer chain is activated mediated by a series of cofactors like chlorophylls, quinones and iron-sulfur clusters. The ultimate goal of this electron transport is to transfer the charge to the other side of the protein where it will be transferred to other enzymes catalyzing substrates. Understanding this procedure would help us creating artificial ways of capturing light energy and directly converting it into clean, renewable chemical energy like bio-fuels, hydrogen and antibiotics.
Reaction Centers Convert and Stabilize Charge-Separated States
Solar energy is by far the most abundant and inherently clean energy source. A fundamental question in the field of artificial photosynthetic systems which aim to efficiently harness solar energy is how to convert and sufficiently stabilize a charge-separated state for desired chemistry to proceed while preventing the energy-wasteful back reaction. In photosynthetic systems, these processes are carried out with almost 100% quantum efficiency, and as such, there is great interest in understanding the basic guiding principles of energy and charge transfer in natural systems. While the static arrangement of the involved cofactors and protein environment are essential for undertaking highly efficient forward reaction, it is thought the dynamics of the protein matrix also play highly critical roles in regulating and stabilizing the charge separated systems. Understanding the fine-tuning of dynamic aspects in natural systems can provide valuable insights to this process. Another related question is how the directionality of charge transfer in photosynthetic reaction centers is achieved and understanding this process will provide answers to how the protein matrix controls charge separation/stabilization.
Serial Femtosecond Crystallography to Study Protein-Cofactor Interactions
In order to determine the subtle changes in the environment of the cofactors of the electron transfer chain in photosynthetic reaction centers, we conduct time-resolved pump-probe X-ray diffraction (XRD) studies at room temperature. The proposed studies rely on the unique capabilities of X-ray free electron lasers (XFELs) which produce ultra-short (5-100’s of femtoseconds) pulses of X-rays of high intensity. The ultrafast temporal structure of the X-ray pulses, together with the exceptional brightness, allow the study of phenomena that are not accessible by synchrotron X-ray methods, either due to the fast time scale of the reaction or low signal levels. With a “measure before destroy” approach using the fs X-ray pulses of an XFel, it is possible to extract radiation damage free data from samples in the femtosecond time scale at room temperature before they are destroyed by coulomb explosion. This approach is called serial femtosecond crystallography (SFX) .
Photosystem I
Photosystem I
from Thermosynechococcus vestitus and Synechocystis sp. PCC6803
Why are we interested in Photosystem I?
Why are we interested in Photosystem I?
Photosystem I (PSI) is membrane protein in the thylakoid membrane of photosynthetic active organisms like plants, algae and cyanobacteria. In our studied organisms PSI is mostly found a trimeric form and consists of 12 subunits per monomer. It harbors two pseudo-symmetrical electron transfer branches which are mediating the ultra-fast and highly efficient electron transfer. The branches are formed by a series of cofactors coordinated by the protein environment. PSI is the most efficient energy converter in nature with a quantum efficiency of nearly 100 %. It harbors two branches of co-factors which are mediating the highly efficient and ultra-fast electron transfer chain within the protein. Understanding how PSI is doing this very efficient energy conversion is absolutely crucial for creating new ways of producing clean, unlimited and renewable energy.
Purple Bacterial Reaction Center
Purple Bacterial Reaction Center
from Rhodobacter sphaeroides
Why are we interested in Purple Bacterial Reaction Center?
Why are we interested in Purple Bacterial Reaction Center?
Bacterial Reaction Center (bRC) is a membrane protein which can be found in purple bacteria. It forms monomers consisting of three subunits. Like the other photosystems it harbors two branches of cofactors responsible for the electron transfer. Although its structure and overall architecture is more similar to PSII its function is closer to PSI due to the missing capability of water splitting. Using bRC as model helps us to understand the dynamics of the protein environment and get insights on how the water network and/or binding network is mediating the electron transfer chain reaction.
Light-harvesting Complex II
Light-harvesting Complex II
from Spinacia oleracea
Why are we interested in Light-harvesting Complex?
Why are we interested in Light-harvesting Complex?
The light-harvesting complex of photosystem II (LHCII) is the main site of light absorption by pigment proteins and energy transfer to the reaction center (PSII) during the initial stages of photosynthesis in plants. Additionally, LHCII functions as the photoprotection site when the plant is exposed to intense light conditions. This project aims to track light-induced changes and possible structural manifestations of the state transition in LHCII throughout the process of photosynthesis. We also want to study the exciton coupling and heat production in LHCII to further understand how the protein regulates the absorption and utilization of photons, especially in intense light conditions.
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