Long-Distance Protonation-Conformation Coupling in Phytochrome Species

• Published in: Molecules (Basel, Switzerland) Vol. 27; no. 23; p. 8395
• Main Authors: Sadeghi, Maryam, Balke, Jens, Rafaluk-Mohr, Timm, Alexiev, Ulrike
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.12.2022; MDPI
• Subjects: Agp1; Anisotropy; Bacterial Proteins - metabolism; Biliverdin; Cellular structure; chromophore protonation; Chromophores; conformational coupling; Correlation; Cph1; Cysteine; Domains; Fluorescence; Labeling; Light; Molecular Conformation; Photoreceptors; Phycocyanobilin; Phytochrome; Phytochrome - chemistry; Phytochromes; Proteins; Protonation; Signal transduction; Soil microbiology; Germany; chromophore protonation; Agp1; phytochrome; Cph1; biliverdin; conformational coupling
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules27238395

Phytochromes are biological red/far-red light sensors found in many organisms. The connection between photoconversion and the cellular output signal involves light-mediated global structural changes in the interaction between the photosensory module (PAS-GAF-PHY, PGP) and the C-terminal transmitter (output) module. We recently showed a direct correlation of chromophore deprotonation with pH-dependent conformational changes in the various domains of the prototypical phytochrome Cph1 PGP. These results suggested that the transient phycocyanobilin (PCB) chromophore deprotonation is closely associated with a higher protein mobility both in proximal and distal protein sites, implying a causal relationship that might be important for the global large-scale protein rearrangements. Here, we investigate the prototypical biliverdin (BV)-binding phytochrome Agp1. The structural changes at various positions in Agp1 PGP were investigated as a function of pH using picosecond time-resolved fluorescence anisotropy and site-directed fluorescence labeling of cysteine variants of Agp1 PGP. We show that the direct correlation of chromophore deprotonation with pH-dependent conformational changes does not occur in Agp1. Together with the absence of long-range effects between the PHY domain and chromophore p , in contrast to the findings in Cph1, our results imply phytochrome species-specific correlations between transient chromophore deprotonation and intramolecular signal transduction.