8a5r
Crystal structure of light-activated DNA-binding protein EL222 from Erythrobacter litoralis crystallized and measured in dark.
Structural highlights
FunctionLVHTH_ERYLH Has reversible, light-dependent DNA-binding activity. Upon illumination an internal FMN-protein adduct is formed which changes the protein conformation so that the previously sequestered DNA-binding domain is free to bind DNA. Binds to sequences within in its own promoter when illuminated but not when it has been incubated in the dark.[1] Publication Abstract from PubMedThe activity of the light-oxygen-voltage/helix-turn-helix (LOV-HTH) photoreceptor EL222 is regulated through protein-protein and protein-DNA interactions, both triggered by photo-excitation of its flavin mononucleotide (FMN) cofactor. To gain molecular-level insight into the photocycle of EL222, we applied complementary methods: macromolecular X-ray crystallography (MX), nuclear magnetic resonance (NMR) spectroscopy, optical spectroscopies (infrared and UV-visible), molecular dynamics/metadynamics (MD/metaD) simulations, and protein engineering using noncanonical amino acids. Kinetic experiments provided evidence for two distinct EL222 conformations (lit1 and lit2) that become sequentially populated under illumination. These two lit states were assigned to covalently bound N5 protonated, and noncovalently bound hydroquinone forms of FMN, respectively. Only subtle structural differences were observed between the monomeric forms of all three EL222 species (dark, lit1, and lit2). While the dark state is largely monomeric, both lit states undergo monomer-dimer exchange. Furthermore, molecular modeling revealed differential dynamics and interdomain separation times arising from the three FMN states (oxidized, adduct, and reduced). Unexpectedly, all three EL222 species can associate with DNA, but only upon blue-light irradiation, a high population of stable complexes is obtained. Overall, we propose a model of EL222 activation where photoinduced changes in the FMN moiety shift the population equilibrium toward an open conformation that favors self-association and DNA-binding. Light-dependent flavin redox and adduct states control the conformation and DNA-binding activity of the transcription factor EL222.,Chaudhari AS, Favier A, Tehrani ZA, Koval T, Andersson I, Schneider B, Dohnalek J, Cerny J, Brutscher B, Fuertes G Nucleic Acids Res. 2025 Mar 20;53(6):gkaf215. doi: 10.1093/nar/gkaf215. PMID:40119733[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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