Crystal structure of a far-red-sensing cyanobacteriochrome reveals an atypical bilin conformation and spectral tuning mechanism.
In: Proceedings of the National Academy of Sciences of the United States of America, Jg. 118 (2021-03-23), Heft 12
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Zugriff:
Cyanobacteriochromes (CBCRs) are small, linear tetrapyrrole (bilin)-binding photoreceptors in the phytochrome superfamily that regulate diverse light-mediated adaptive processes in cyanobacteria. More spectrally diverse than canonical red/far-red-sensing phytochromes, CBCRs were thought to be restricted to sensing visible and near UV light until recently when several subfamilies with far-red-sensing representatives (frCBCRs) were discovered. Two of these frCBCRs subfamilies have been shown to incorporate bilin precursors with larger pi-conjugated chromophores, while the third frCBCR subfamily uses the same phycocyanobilin precursor found in the bulk of the known CBCRs. To elucidate the molecular basis of far-red light perception by this third frCBCR subfamily, we determined the crystal structure of the far-red-absorbing dark state of one such frCBCR Anacy_2551g3 from Anabaena cylindrica PCC 7122 which exhibits a reversible far-red/orange photocycle. Determined by room temperature serial crystallography and cryocrystallography, the refined 2.7-Å structure reveals an unusual all-Z,syn configuration of the phycocyanobilin (PCB) chromophore that is considerably less extended than those of previously characterized red-light sensors in the phytochrome superfamily. Based on structural and spectroscopic comparisons with other bilin-binding proteins together with site-directed mutagenesis data, our studies reveal protein-chromophore interactions that are critical for the atypical bathochromic shift. Based on these analyses, we propose that far-red absorption in Anacy_2551g3 is the result of the additive effect of two distinct red-shift mechanisms involving cationic bilin lactim tautomers stabilized by a constrained all-Z,syn c onformation and specific interactions with a highly conserved anionic residue.
Competing Interests: The authors declare no competing interest.
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Crystal structure of a far-red-sensing cyanobacteriochrome reveals an atypical bilin conformation and spectral tuning mechanism.
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Autor/in / Beteiligte Person: | Bandara, S ; Rockwell, NC ; Zeng, X ; Ren, Z ; Wang, C ; Shin, H ; Martin, SS ; Moreno, MV ; Lagarias, JC ; Yang, X |
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Zeitschrift: | Proceedings of the National Academy of Sciences of the United States of America, Jg. 118 (2021-03-23), Heft 12 |
Veröffentlichung: | Washington, DC : National Academy of Sciences, 2021 |
Medientyp: | academicJournal |
ISSN: | 1091-6490 (electronic) |
DOI: | 10.1073/pnas.2025094118 |
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