ABSTRACT
Photosynthetic reaction centres harvest the energy content of sunlight by transporting electrons across an energy-transducing biological membrane. Here we use time-resolved serial femtosecond crystallography1 using an X-ray free-electron laser2 to observe light-induced structural changes in the photosynthetic reaction centre of Blastochloris viridis on a timescale of picoseconds. Structural perturbations first occur at the special pair of chlorophyll molecules of the photosynthetic reaction centre that are photo-oxidized by light. Electron transfer to the menaquinone acceptor on the opposite side of the membrane induces a movement of this cofactor together with lower amplitude protein rearrangements. These observations reveal how proteins use conformational dynamics to stabilize the charge-separation steps of electron-transfer reactions.
Subject(s)
Photosynthetic Reaction Center Complex Proteins/chemistry , Photosynthetic Reaction Center Complex Proteins/metabolism , Bacteriochlorophylls/metabolism , Binding Sites/drug effects , Chlorophyll/metabolism , Chlorophyll/radiation effects , Crystallography , Cytoplasm/metabolism , Electron Transport/drug effects , Electrons , Hyphomicrobiaceae/enzymology , Hyphomicrobiaceae/metabolism , Lasers , Models, Molecular , Oxidation-Reduction/radiation effects , Pheophytins/metabolism , Photosynthetic Reaction Center Complex Proteins/radiation effects , Protons , Ubiquinone/analogs & derivatives , Ubiquinone/metabolism , Vitamin K 2/metabolismABSTRACT
Low-frequency vibrations are crucial for protein structure and function, but only a few experimental techniques can shine light on them. The main challenge when addressing protein dynamics in the terahertz domain is the ubiquitous water that exhibit strong absorption. In this paper, we observe the protein atoms directly using X-ray crystallography in bovine trypsin at 100 K while irradiating the crystals with 0.5 THz radiation alternating on and off states. We observed that the anisotropy of atomic displacements increased upon terahertz irradiation. Atomic displacement similarities developed between chemically related atoms and between atoms of the catalytic machinery. This pattern likely arises from delocalized polar vibrational modes rather than delocalized elastic deformations or rigid-body displacements. The displacement correlation between these atoms were detected by a hierarchical clustering method, which can assist the analysis of other ultra-high resolution crystal structures. These experimental and analytical tools provide a detailed description of protein dynamics to complement the structural information from static diffraction experiments.
