Until the end of last century, the natural photoenzymes known were (i) Photosystem I and II as a unit, photocatalysing water decomposition into O2 and H+, (ii) protochlorophyllide reductase photocatalysing chlorophyllide production (with NADPH as cofactor) and (iii) photolyases as DNA repair enzymes in many organisms (except mammals) with a reduced flavin adenine dinucleotide (FADH-) as chromophore and a second flavin or a pterin as a second cofactor.
Since the beginning of the new millenium several biological photoreceptors have been characterized as photoenzymes. Among those containing a flavin as chromophore, adenylyl cyclases[1] are found in microorganisms and photodercaboxylases in algae.[2] In other microorganisms enzymerhodopsins act as kinases, cyclases or phosphodiesterases, all of them with retinal as chromophore.[3]
Photosensors containing an open-chain tetrapyrrole chromophore have also being characterized as photoenzymes. Microbial phytochromes act as light regulated histidine kinases or phosphatases in two component systems[4] and cyano-bacteriochromes in cyanobacteria are adenylyl cyclases.[5] It has also been shown that eucaryote phytochromes are protein kinases as well as autophosphorylation kinases.[6],[7]
The diversity of chromophores in different protein matrices and the knowledge about the function of the natural photoenzymes offer multiple possibilities to mimic the biosystems and design photoenzymes excitable with a wide range of wavelengths to perform different, non-natural tasks, with ecological advantages, e.g., by replacing chemical reactions in organic solvents with metal-containing catalysers, extensively used in the chemical industry.
[1] Stierl et al, J. Biol. Chem. 286, 1181-1188 (2011)
[2] Sorigué et al, Science 357, 903-907 (2017)
[3] Mukherjee et al, Current Op. Struct. Biol. 57, 118-126 (2019)
[4] Multamäki et al, Nature Commun. 12, 4394-4407 (2021)
[5] Blain-Hartung et al, J. Biol. Chem. 293, 8473-8483 (2018)
[6] Quyen T. N. Hoang et al, Int. J. Mol. Sc. 20, 3450-3465 (2019)
[7] Han Y-J, et al, Front. Plant Sci. 15:1259720. (2024) doi: 10.3389/fpls.2024.1259720