6UVB

Crystal structure of far-red-light absorbing cyanobacteriochrome at 100K

Summary for 6UVB

• Entry DOI: 10.2210/pdb6uvb/pdb
• Related: 6UV8
• Descriptor: Multi-sensor signal transduction histidine kinase, PHYCOCYANOBILIN (3 entities in total)
• Functional Keywords: photoreceptor, bilin-binding protein, signaling protein, far-red light
• Biological source: Anabaena cylindrica (strain ATCC 27899 / PCC 7122)
• Total number of polymer chains: 1
• Total formula weight: 22644.74

Authors

Yang, X.,Ren, Z.,Bandara, S. (deposition date: 2019-11-01, release date: 2020-11-04, Last modification date: 2024-10-09)

Primary citation

Bandara, S.,Rockwell, N.C.,Zeng, X.,Ren, Z.,Wang, C.,Shin, H.,Martin, S.S.,Moreno, M.V.,Lagarias, J.C.,Yang, X.
Crystal structure of a far-red-sensing cyanobacteriochrome reveals an atypical bilin conformation and spectral tuning mechanism.
Proc.Natl.Acad.Sci.USA, 118:-, 2021

PubMed Abstract: 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 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 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 onformation and specific interactions with a highly conserved anionic residue.

PubMed: 33727422
DOI: 10.1073/pnas.2025094118

Experimental method

X-RAY DIFFRACTION (3 Å)