Light is an energy source that supports life on planet Earth. It is also a signal to regulate key biological processes that affect growth, biological adaptation, reproduction and development. There are a number of photoreceptors found in nature and these have huge potential in controlling a range of biochemical processes through engineering in global grand challenge programs. These include crop engineering, plant adaptation to agricultural environments, light-mediated regulation of cyanobacteria/algae in synthetic biofuels/energy programs, as well as offering exciting opportunities in the field of optogenetics. We are providing in-depth structural-mechanistic and biophysical understanding of light-activated signalling in several photoreceptor proteins and seek to understand how light capture drives biological responses through signalling and the coupling of small/fast structural vibrations (photochemistry) to major thermally-driven large/slow protein rearrangements. We are using state-of-the-art biophysical and structural tools to understand mechanisms of light responsive signalling, drawing on laser and conventional spectroscopies, structural biology and computational methods.
Phytochromes / Cyanobacteriochromes
These are major light-responsive proteins that regulate a range of biological responses in plants and microorganisms, including time of flowering, circadian clock, seed germination, phototaxis, chlorophyll synthesis, cell adhesion, movement of light-harvesting complexes, leaf formation, plus many others.is challenging. They contain a bilin cofactor and signalling is initiated by photoconversion between 2 states of the chromophore which is then linked to structural change in an output/regulatory domain to control output activity. There are opportunities for modifying phytochrome and/or cyanobacteriochrome spectral responses, and the engineering of novel photosensory pathways that affect biological outcomes in each of these exploitation environments. A current limitation to exploitation of these light-responsive proteins is the lack of detailed mechanistic, functional and structural knowledge required to drive these novel proteins towards applications in global grand challenge programs.
Protochlorophyllide Oxidoreductase (POR)
This is one of only three naturally light-dependent enzymes found in nature. By using a combination of state-of-the-art time-resolved (fs – s) and cryogenic spectroscopy methods we have developed mechanistic understanding of POR enzymes from different photosynthetic organisms, including cyanobacteria and higher plants. Notably, we have suggested that excited state interactions between the substrate protochlorophyllide (Pchlide) and active site residues trigger the reaction cycle. This involves picosecond excited state dynamics followed by sequential hydride (H-) transfer from NADPH and a proton (H+) transfer on the microsecond timescale. We are now working towards putting the reaction mechanism into a structural context in order to understand how excited state chemistry, bond making/breaking and the dynamics of catalysis, binding and release are controlled by protein structure.
These are blue light photoreceptor flavoproteins that are found in plants, animals and microorganisms. They are involved in a number of biological responses, including synchronisation of the circadian clock in animals, and seed germination and pigment accumulation in plants. The precise photochemical mechanism still remains unclear but is proposed to involve excited state electron transfer between the flavin and conserved Trp residues (see figure C) in the protein. We aim to understand the photochemistry in detail and study the formation of radical pairs in the reaction mechanism.
Vitamin B12-dependent photoreceptors (e.g. CarH)
This photoreceptor is proposed to regulate gene regulation in certain bacteria. In the dark, the CarH monomer forms a tetramer on binding of AdoCbl, which then binds DNA. Aerobic photolysis of CarH-bound AdoCbl causes the tetramer to dissociate, thus activating gene expression. Little is known about the photophysical and photochemical mechanism and this is the focus of our work.
Some Recent Photobiology Publications:
Photochemical mechanism of an atypical algal phytochrome (2018) U.Choudry, D.J. Heyes, S.J.O. Hardman, M. Sakuma, I.V. Sazanovich, J. Woodhouse, E. De La Mora, M. Pedersen, M. Wulff, M. Weik, G. Schiro, N.S. Scrutton, ChemBioChem, 19, 1036-1043, DOI: 10.1002/cbic.201800016 . Featured on front cover
Stepwise hydride transfer in a biological system: insights into the reaction mechanism of the light-dependent protochlorophyllide oxidoreductase (2018) N. Archipowa, R.J. Kutta, D.J. Heyes and N.S. Scrutton, Angewandte Chemie, 57, 10, 2682-2686, DOI:10.1002/anie.201712729
Vertebrate cryptochromes are vestigial flavoproteins (2017) R. J. Kutta, N. Archipowa, L. O. Johannissen, A.R. Jones, N. S. Scrutton Scientific Reports, 7, 44906, DOI: 10.1038/srep44906
Direct evidence of an excited state triplet species upon photoactivation of the chlorophyll precursor protochlorophyllide (2017) G. Brandariz-de-Pedro, D.J. Heyes, S.J.O. Hardman, M.Shanmugam, A.R. Jones, S. Weber, D. Nohr, N.S. Scrutton, A.J. Fielding, Journal of Physical Chemistry Letters, 8 (6), 1219–1223, DOI: 10.1021/acs.jpclett.7b00200
Excited state properties of protochlorophyllide analogues and implications for light driven synthesis of chlorophyll (2017) Heyes, D. J., Hardman, S. J. O., Mansell, D., Ní Cheallaigh, A., Gardiner, J. M., Johannissen, L. O., Greetham, G. M., Towrie, M., Scrutton, N. S., Journal of Physical Chemistry B., 121, 1312-1320, DOI: 10.1021/acs.jpcb.7b00528