S C

IE N

T IF

IC H

IG H

LI G

H T

S S

T R

U C

T U

R A

L B

IO LO

G Y

5 1 I H I G H L I G H T S 2 0 2 1

indicated that the FAD cofactor is bent in its oxidised form. Room-temperature serial femtosecond crystallography (SFX) was performed for radiation-damage-free diffraction data. This SFX dark-state structure of FAP, solved at 2.0Å resolution, features a FAD with a similar bending angle (14.3°). This FAD conformation has not been firmly established for any other flavoprotein. Future radiation- damage-free structures of oxidised flavoproteins should reveal whether the bending is a feature specific to FAP.

Time-resolved infrared spectroscopy demonstrated that decarboxylation occurred quasi-instantaneously upon the first (forward) electron transfer, consistent with barrier-

less bond cleavage predicted by quantum chemistry calculations and with snapshots obtained by time-resolved crystallography. Transient absorption spectroscopy in H2O and D2O buffers indicated that back electron transfer was coupled to and limited by transfer of an exchangeable proton or hydrogen atom (Figure 38, step 3). Unexpectedly, most of the CO2 product was converted, most likely into bicarbonate (as inferred from FTIR spectra of the cryo- trapped FAD red shifted intermediate). Calculations indicated that this catalytic transformation involved an active-site water molecule. Cryo-FTIR studies suggested that bicarbonate formation (Figure 38, step 4) was preceded by deprotonation of an arginine residue (step 3). At room temperature, the remaining CO2 leaves the protein in 1.5 μs (step 4 ). The observation of residual electron density close to C432 in electron density maps derived from time-resolved and cryo-crystallography data suggests that this residue may play a role in stabilising CO2 and/or bicarbonate, whereas R451 stabilises the substrate and serves as the catalytic residue through a proton- coupled electron transfer reaction.

Fig. 38: Elucidation of the FAP photocycle by combining spectroscopic, biochemical, crystallographic, and computational studies. From D. Sorigué et al., Mechanism and dynamics of fatty acid photodecarboxylase, Science 372, 6538 (2021). Reprinted with permission from AAAS.

PRINCIPAL PUBLICATION AND AUTHORS

Mechanism and dynamics of fatty acid photodecarboxylase, D. Sorigué (a), K. Hadjidemetriou (b), S. Blangy (a), G. Gotthard (c), A. Bonvalet (d), N. Coquelle (e), P. Samire (a,f), A. Aleksandrov (d), L. Antonucci (d), A. Benachir (d), S. Boutet (g), M. Byrdin (b), M. Cammarata (h), S. Carbajo (g), S. Cuiné (a), R.B. Doak (i), L. Foucar (i), A. Gorel (i), M. Grünbein (i), E. Hartmann (i), R. Hienerwadel (a), M. Hilpert (i), M. Kloos (i), T.J. Lane (g), B. Légeret (a), P. Legrand (j), Y. Li-Beisson (a), S.L.Y. Moulin (a), D. Nurizzo (c), G. Peltier (a), G. Schirò (b), R.L. Shoeman (i), M. Sliwa (k), X. Solinas (d), B. Zhuang (d,f), T.R.M. Barends (i), J.-P. Colletier (b), M. Joffre (d), A. Royant (b,c), C. Berthomieu (a), M. Weik (b), T. Domratcheva (i,l), K. Brettel (f), M.H. Vos (d), I. Schlichting (i), P. Arnoux (a), P. Müller (f), F. Beisson (a), Science 372, 6538 (2021); https:/doi.org/10.1126/science.abd5687

(a) Aix-Marseille University, Institute of Biosciences and Biotechnologies, BIAM Cadarache (France) (b) Université Grenoble Alpes, Institut de Biologie Structurale, Grenoble (France) (c) ESRF (d) LOB, Ecole Polytechnique, Institut Polytechnique de Paris, Palaiseau (France) (e) Large-Scale Structures Group, Institut Laue Langevin, Grenoble (France) (f) Université Paris-Saclay, Institute for Integrative Biology of the Cell, Gif-sur-Yvette (France) (g) Linac Coherent Light Source, SLAC National Accelerator Laboratory, California (USA) (h) Department of Physics, University of Rennes 1 (France) (i) Max-Planck-Institut für medizinische Forschung, Heidelberg (Germany) (j) Synchrotron SOLEIL, Gif-sur-Yvette (France) (k) Université Lille, Laboratoire de Spectroscopie pour les Interactions, la Réactivité et l Environnement, Lille (France) (l) Department of Chemistry, Lomonosov Moscow State University (Russia)

REFERENCES

[1] D. Sorigué et al., Science 357, 903-907 (2017).