The blue-light receptor cryptochrome (CRY) in plants undergoes oligomerization to transduce blue-light signals after irradiation, but the corresponding molecular mechanism remains poorly understood. Here, we report the cryogenic electron microscopy structure of a blue-light-activated CRY2 tetramer at a resolution of 3.1 Å, which shows how the CRY2 tetramer assembles. Our study provides insights into blue-light-mediated activation of CRY2 and a theoretical basis for developing regulators of CRYs for optogenetic manipulation.
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Atomic coordinates and structure factors of blue light activated CRY2 tetramer have been deposited in the Protein Data Bank under accession codes PDB 6M79. The cryo-EM map of this tetramer has been deposited in the EM Database with accession code EMD-30128. Source data for Fig. 1b, Extended Data Figs. 6, 7 and 9, and Supplementary Fig. 4 are provided with this paper online. The structures of CRY2N monomer under darkness (PDB accession code 6K8I), BIC2-CRY2N complex (PDB accession code 6K8K), and ZmCRY1cW368A tetramer (PDB accession code 6LZ3) used in this study had been reported (https://doi.org/10.1038/s41594-020-0410-z and https://doi.org/10.1038/s41594-020-0420-x). Source data are provided with this paper.
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We are grateful to the Cryo-EM Facility Center of Southern University of Science and Technology for providing technical support during EM image acquisition. We thank the research associates at the Center for Protein Research and Public Laboratory of Electron Microscopy, Huazhong Agricultural University, for technical support. We also thank X. L. Qu, College of Horticulture and Forestry Sciences of Huazhong Agricultural University, for technical support on fluorescence microscopy. We thank Q. Wang from Fujian Agriculture and Forestry University for her constructive suggestions during paper preparation. This work was supported by funds from the Ministry of Science and Technology of China (2018YFA0507700), the National Natural Science Foundation of China (31722017 and 31870753), the Fok Ying-Tong Education Foundation (151021), and the Fundamental Research Funds for the Central Universities (2662017PY031).
The authors declare no competing interests.
Peer review information Nature Plants thanks the anonymous reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Processing of 3036 movie stacks resulted in a total number of 3,252,248 particles. After 2D classification, 3,178,552 particles were kept and subjected to 3D classifications. The best 209,604 particles from one class were retained for further 3D auto-refinement for which C2 symmetry was applied, resulting in a 3.1 Å density map estimated on the basis of the gold-standard Fourier shell correlation with 0.143 criterion.
a, Representative Cryo-EM micrograph of CRY2 oligomer. Experiments were independently repeated three times with similar results. b, Selected reference-free 2D classification averages. 2D classification of CRY2 oligomer particles representing tetramer-like fold. c, Angular distribution plot for the final reconstruction from two different views. d, Local resolution of the Cryo-EM map generated by ResMap colored from blue to red to indicate resolution from high to low (side bar). e, Gold-standard Fourier Shell Correlation curve for CRY2 tetramer reconstruction. f, Fourier Shell Correlation curve of the model versus the map used for model refinement.
a, Cryo-EM density for reduced FAD and interacting residues. b, Cryo-EM density for AMP and interacting residues. c, Cryo-EM density for CRY2N tetramer helices and sheets.
Static light scattering analyses of CRY2 PHR molecular weight in darkness and under blue light, respectively. All runs were performed in a Superdex 200TM increase 10/300 GL column. The corresponding CRY2 PHR molecular weights for the two conditions were 44±0.24 kDa and 173±1.95 kDa, respectively.
a, Two interfaces of tetramer. CRY2 tetramer is comprised of mol A, B, C, and D that are shown as light pink, cyan, light blue, and yellow, respectively. Connector regions are colored in magenta, red, blue, and green, respectively. Red and black squares show close-up views of interface 1 and interface 2 with 90° rotations, respectively. Numbered helices are involved in the tetramerization. b, Schematic representation of CRY2 tetramer interactions. Extensive interaction networks of interface 1 and interface 2. Residues in mol A, mol B, and mol C involved in interactions are indicated by purple, dark green, and light blue rectangles, respectively. In interface 1, E18 in helix α1; H62 and S66 in helix α3; D160 in helix α6; M167 and R173 in the loop of the connector region; N222 in helix α8; and M267 and R274 in helix α11 from mol A coordinate with M267, R274, R173, M167, D160, N222, E18, H62, and S66 from mol B via hydrogen bonds, respectively (left panel black dashed lines). I17, L159, I163, W172, W214, F262, M267, I270, and I271 interact with each other via hydrophobic interactions (left panel black solid line). Interface 2 is mainly mediated by a dozen hydrogen bonds formed by R50, S202, K329, Q333, R346, W349, E436, R439, A458, and E462 from the two protomers.
a, Oligomerization state of wild type (WT) and mutated CRY2 measured by pull-down assays. Mammalian cells (Expi293F) were co-transfected with constructs designed to express the indicated proteins. The supernatant from lysed cells was incubated with StrepII beads under blue light (50 μmol m−2s−1) or in darkness for 1.5 h. Proteins in input and eluted fractions were detected by immunoblots probed with antibodies against StrepII and Myc. Residues critical for oligomerization are labeled in red. b, Quantification of results in a. The integrated densities of different bands were measured using Image J software. The pull-down prey bands under blue light were normalized by both input and bait bound. Mutants with pull-down bands lower than 20% percent of wild type were shown in red column. The standard deviation is derived from three measurements. Data were presented as mean ± SD. Black circles indicate individual data points for n=3 biological replicates. Differences between each mutants and wild type CRY2 were analyzed by two-tailed paired t-tests. Means with p < 0.05 are indicated. *, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001. Experiments in a were repeated three times, with similar results. Uncropped blot images are available as source data. Source data
a, Photobodies formation of CRY2 WT and CRY2 mutants. It was reported that CRY2-GFP, but not GFP-CRY2, forms photobodies in response to blue light19. GFP was constructed to the C-terminal of these CRY2 mutants. B: blue. Bars = 5 μm. b, Percent of cells with photobodies which is calculated by [total number of cells with photobodies in a field of view] / [the number of total cells in the same field view]. The standard deviation is derived from n=80 cells examined 3 independent experiments. Data were presented as mean ± SD. Black circles indicate individual data points for 3 biological replicates. Differences between each mutants and wild type CRY2-GFP were analyzed by two-tailed paired t-tests. Means with p < 0.05 are indicated. *, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001. Source data
The FAD/Reduced FAD binding cavities were defined as forming by the residues that possess distances within 4.5 Å to the FAD/Reduced FAD cofactor, and the cavity volume was calculated using POVME23.
All the rans were performed in a SuperoseTM 6 increase 10/300 GL column. Left panel shows SEC analyses of CRY2WT (in darkness and under blue light), CRY2Y232F, CRY2Y232A, CRY2W353A and CRY2W353F. In darkness, wild type CRY2 eluted at 16.5 ml (deep teal line). Whereas, after blue light treatment, activated CRY2 eluted at 14.3 ml (dark purple line), indicating that CRY2 formed a tetramer. In darkness, CRY2Y232A (orange line) and a part of CRY2W353A (peak 1 of red line) eluted at around 14.8 ml, which is similar to that of CRY2WT under blue light, indicating CRY2Y232A and CRY2W353A are tetramers. CRY2Y232F (brown line) and CRY2W353F (green line) were eluted at 16.5 ml, indicating they were monomer. Right panel shows SEC analyses of CRY2WT (in darkness and under blue light), CRY2T244A, CRY2S245A, CRY2N356A and CRY2D387A. Coomassie blue-stained SDS-PAGE gels of peak fractions are on the right of corresponding SEC lines. Experiments were independently repeated three times with similar results. Uncropped gel images are available as source data. Source data
Extended Data Fig. 10 Intra protein hydrophobic interactions of W374 in CRY2N monomer and superposition of structures of blue-light activated CRY2WT tetramer with ZmCRY1W368A tetramer and BIC2-CRY2N complex.
a, CRY2N is shown in white and FAD binding cavity helices are shown in cyan. The black square shows a close-up view of residues that form intra protein hydrophobic interactions with W374. b, Superposition of structures of blue light induced AtCRY2NWT tetramer (in this study) and PHR domain of ZmCRY1W368A tetramer (PDB 6LZ3). c, Structure alignment of CRY2N tetramer (in this study) with BIC2-CRY2N complex (PDB 6K8K). Mol A and D are shown in white; Mol B and C are shown in wheat. BIC2 is shown in red. Surface and ribbon representation of BIC2 is shown. Black dashed lines indicate the clash between BIC2 and interface 2. The black square shows a close-up view of the clash with a 90° rotation.
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Ma, L., Guan, Z., Wang, Q. et al. Structural insights into the photoactivation of Arabidopsis CRY2. Nat. Plants 6, 1432–1438 (2020). https://doi.org/10.1038/s41477-020-00800-1