Biology subjects

Koval, T.

Publications and source records attributed to Koval, T..

3 recordsLinked to original sources

bioRxiv2024

Light-dependent flavin redox and adduct states control the conformation and DNA binding activity of the transcription factor EL222

The activity of the transcription factor EL222 is regulated through protein-chromophore adduct formation, interdomain dynamics, oligomerization and protein-DNA interactions, all 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 non-canonical amino acids. The observation of only subtle atomic displacements between crystal structures of EL222 with and without blue-light back-illumination, was confirmed by NMR data indicating no major changes in secondary structure and fold compactness. Kinetic experiments in solution 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 non-covalently-bound hydroquinone forms of FMN, respectively. Molecular modeling revealed differential dynamics and domain separation times arising from the three FMN states (oxidized, adduct, and reduced). Furthermore, while the dark state is largely monomeric, both lit states undergo slow monomer-dimer exchange. The photoinduced loss of -helicity, seen by infrared difference spectroscopy, was ascribed to dimeric EL222 species. Unexpectedly, NMR revealed that all three EL222 species (dark, lit1, lit2) can associate with DNA to some extent, but only under illumination a high population of stable complexes is obtained. Overall, we propose a refined model of EL222 photo-activation where photoinduced changes in the oxidation state of FMN and thioadduct formation shift the population equilibrium towards an open conformation that favors self-association and DNA-binding. Significance StatementFlavin-binding light-oxygen-voltage (LOV) proteins constitute a prominent example of highly evolved chromophore-containing proteins that convert light into biochemical changes in the cell. However, it is not well understood how blue-light orchestrates changes in LOV structure and function. Here we show that the dynamics, oligomerization and DNA-binding properties of the photocontrolled transcription factor EL222 are dependent on both the flavin redox state and thioadduct formation. In the dark, monomeric EL222 forms transient encounter complexes with DNA. Under illumination, two distinct lit states are sequentially generated, termed lit1 and lit2, that are both able to assemble into EL222:DNA (2:1) complexes. Our results reveal the coupling between flavin photochemistry (protonation and covalent linkage) and fold stability in EL222 and potentially other flavoproteins.

biochemistry↗

bioRxiv2021

Crystal structure of the human NKR-P1 bound to its lymphocyte ligand LLT1 reveals receptor clustering in the immune synapse

Human NKR-P1 (CD161, KLRB1) and its ligand LLT1 (CLEC2D) are a prototypical inhibitory C-type lectin-like receptor:ligand pair of NK cells with a critical role in homing lymphocytes to immune-privileged sites, particularly in multiple sclerosis, rheumatoid arthritis, and Crohns disease. Furthermore, NKR-P1:LLT1 inhibitory signaling is associated with glioblastoma, non-Hodgkins lymphoma, breast, and prostate cancer. However, the lack of structural data on the formation of the NKR-P1:LLT1 complex limits our understanding of this signaling. We thus solved the crystal structures of NKR-P1 and the NKR-P1:LLT1 complex. NKR-P1 forms a homodimer with an unexpected arrangement that enables LLT1 binding in two modes, bridging two LLT1 molecules, thereby forming interaction clusters suggestive of an inhibitory immune synapse. Moreover, observing the formation of these clusters by SEC-SAXS analysis in solution and by dSTORM super-resolution microscopy on the cell surface, and following their role in receptor signaling using in vitro cytotoxicity assay with freshly isolated NK cells, we show how NKR-P1:LLT1 clustering allows these proteins to overcome the weak affinity of C-type lectin-like receptors to their ligands. Furthermore, only the ligation of both primary and secondary LLT1 binding interfaces leads to effective NKR-P1 inhibitory signaling. Therefore, our findings show how inhibitory receptor cross-linking and clustering work together to trigger signal transduction upon cellular contact in the immune synapse.

molecular biology↗

bioRxiv2020

Mycobacterial HelD is a nucleic acids-clearing factor for RNA polymerase

RNA synthesis is central to life, and RNA polymerase depends on accessory factors for recovery from stalled states and adaption to environmental changes. Here we investigated the mechanism by which a helicase-like factor HelD recycles RNA polymerase. We report a cryo-EM structure of an unprecedented complex between the Mycobacterium smegmatis RNA polymerase and HelD. The crescent-shaped HelD simultaneously penetrates deep into two RNA polymerase channels that are responsible for DNA binding and substrate delivery to the active site, thereby locking RNA polymerase in an inactive state. We show that HelD prevents non-specific interactions between RNA polymerase and DNA and dissociates transcription elongation complexes, but does not inhibit RNA polymerase binding to the initiation {sigma} factor. The liberated RNA polymerase can either stay dormant, sequestered by HelD, or upon HelD release, restart transcription. Our results provide insights into the architecture and regulation of the highly medically-relevant mycobacterial transcription machinery and define HelD as a clearing factor that removes undesirable nucleic acids from RNA polymerase.

molecular biology↗