Unlike canonical phytochromes, the GAF domain of cyanobacteriochromes (CBCRs) can
bind bilins autonomously and is sufficient for functional photocycles. Despite the astonishing spectral
diversity of CBCRs, the GAF1 domain of the three-GAF-domain photoreceptor all2699 from the
cyanobacterium Nostoc 7120 is the only CBCR-GAF known that converts from a red-absorbing (Pr) dark
state to a far-red-absorbing (Pfr) photoproduct, analogous to the more conservative phytochromes.
Here we report a solid-state NMR spectroscopic study of all2699g1 in its Pr state. Conclusive NMR
evidence unveils a particular stereochemical heterogeneity at the tetrahedral C31 atom, whereas
the crystal structure shows exclusively the R-stereochemistry at this chiral center. Additional NMR
experiments were performed on a construct comprising the GAF1 and GAF2 domains of all2699,
showing a greater precision in the chromophore–protein interactions in the GAF1-2 construct. A 3D
Pr structural model of the all2699g1-2 construct predicts a tongue-like region extending from the
GAF2 domain (akin to canonical phytochromes) in the direction of the chromophore, shielding it
from the solvent. In addition, this stabilizing element allows exclusively the R-stereochemistry for
the chromophore-protein linkage. Site-directed mutagenesis performed on three conserved motifs in
the hairpin-like tip confirms the interaction of the tongue region with the GAF1-bound chromophor
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:88947 |
| Date | 10 January 2024 |
| Creators | Xu, Qian-Zhao, Bielytskyi, Pavlo, Otis, James, Lang, Christina, Hughes, Jon, Zhao, Kai-Hong, Losi, Aba, Gärtner, Wolfgang, Song, Chen |
| Publisher | MDPI |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:article, info:eu-repo/semantics/article, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 3656, 10.3390/ijms20153656 |
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