Abstract
Strigolactones (SLs) regulate many aspects of plant development, but ambiguities remain about how this hormone is perceived because SL-complexed receptor structures do not exist. We find that when SL binds the Striga receptor, ShHTL5, a series of conformational changes relative to the unbound state occur, but these events are not sufficient for signalling. Ligand-complexed receptors, however, form internal tunnels that posit an explanation for how SL exits its receptor after hydrolysis.
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Data availability
All data supporting the findings of this study are available within the paper, its Extended Data and Supplementary Information. The crystallographic structure of GR24-bound ShHTL5 was deposited at the Protein Data Bank with PDB ID 8DVC. Any additional information or materials will be shared by the authors upon request.
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Acknowledgements
A.A.-S. was partially funded by the Mexican National Council of Science and Technology (CONACyT) and by a Mitacs Globalink Graduate Scholarship. This work was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant (no. 06752), an NSERC Accelerator Supplement (no. 507992), an NSERC Research Tools and Instruments grant (no. 00356), a New Frontiers in Research Fund (NFRFE-2018-00118) awarded to S.L. as well as an NSERC Discovery Grant (no. 04298) awarded to P.M. Research was also supported by Compute Ontario (https://computeontario.ca/) and Compute Canada (www.computecanada.ca). We thank R. DiLeo, O. Onopriyenko, M. Venkatesan, M. Bunsick and J. Bradley for support and technical advice.
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A.A.-S., P.J.S. and P.M. conceptualized the research. A.A.-S., T.S. and Z.X. performed experiments. C.S.P.M., A.S. and P.J.S. contributed new reagents and/or analysis tools. A.A.-S., A.S., S.L., P.J.S. and P.M. analysed and/or discussed data with input from all authors. A.A.-S., P.M. and P.J.S. prepared the manuscript. All authors reviewed and agreed on the manuscript.
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Nature Plants thanks Marek Marzec, Tadao Asami and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data
Extended Data Fig. 1 Control pairwise structure alignments of ShHTL5 and ShHTL5S95A.
Control pairwise structure alignments performed on A. apo ShHTL5 (white) and an AlphaFold2 model of itself (blue) and B. ShHTL5S95A (purple) against an AlphaFold2 model of itself (blue). Magnified views show the high agreement between the catalytic triads of crystal structures and models. Both alignments show global RMSD values below 0.20 Å.
Extended Data Fig. 2 Structural models of the GID1 GA receptor and its transport tunnels.
Internal transport tunnels (red) change in shape, size, and orientation in response to gibberellic acid (GA) binding and the presence of its binding partner DELLA.
Supplementary information
Supplementary Information
PDB validation report for the crystallographic structure of ShHTL5-GR24.
Supplementary Video 1
Structural changes of ShHTL5 in response to +GR24 binding. The perception and binding mechanisms of an SL by ShHTL5 are shown, using apo ShHTL5 (PDB 5CBK) as a reference. The perception occurs in 3 phases: first, Phe134, Tyr157 and Lys218 move to accommodate GR24. Second, a group of residues located on the left lid domain change the conformation of their rotamers, creating more space in the binding pocket. Finally, the flexibility loop changes its position to bind to the downstream partner MAX2.
Supplementary Video 2
Molecular dynamics simulation displays an exit cavity forming upon GR24 binding. This movie shows the 1 µs molecular dynamics simulations of apo ShHTL5 and +GR24-bound ShHTL5. The exit end of the SL-enlarged tunnel can be observed only on the bound structure, depicted with an orange circle. MD movies represent one of three trajectories (n = 3) analysed.
Supplementary Video 3
MD simulation of the transport of SL hydrolysis product through internal tunnel of ShHTL5. This movie shows a 1 µs MD simulation of an SL hydrolysis product (PDB 4IHA) moving through the ShHTL5 transport tunnel. It can be observed how the topological landscape of the tunnel changes in response to the product approaching certain areas (that is, bottlenecks). Once the SL is positioned close to the end of the tunnel, the exit cavity is enlarged, possibly to facilitate its expulsion.
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Arellano-Saab, A., Skarina, T., Xu, Z. et al. Structural analysis of a hormone-bound Striga strigolactone receptor. Nat. Plants 9, 883–888 (2023). https://doi.org/10.1038/s41477-023-01423-y
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DOI: https://doi.org/10.1038/s41477-023-01423-y
