Biology subjects

Hörberg, J.

Publications and source records attributed to Hörberg, J..

5 recordsLinked to original sources

bioRxiv2023

Decoding the Dual Recognition Mechanism of Glucocorticoid Receptor for DNA and RNA: Sequence vs. Shape.

Transcription factors (TFs) regulate eukaryotic transcription through selecting DNA-binding, can also specifically interact with RNA, which may present another layer of transcriptional control. The mechanisms of the TFs-DNA recognition are often well-characterised, while the details of TFs-RNA complexation are less understood. Here we investigate the dual recognition mechanism of the glucocorticoid receptor (GR), which interacts with similar affinities with consensus DNA and diverse RNA hairpin motifs but discriminates against uniform dsRNA. Using atomic molecular dynamics simulations, we demonstrate that the GR binding to nucleic acids requires a wide and shallow groove pocket. The protein effectively moulds its binding site within DNA major groove, which enables base-specific interactions. Contrary, the GR binding has little effect on the grooves geometry of RNA systems, most notably in uniform dsRNA. Instead, a hairpin motif in RNA yields a wide and shallow major groove pocket, allowing the protein to anchor itself through nonspecific electrostatic contacts with RNA backbone. Addition of a bulge increases RNA hairpin flexibility, which leads to a greater number of GR-RNA contacts and, thus, higher affinity. Thus, the combination of structural motifs defines the GR-RNA selective binding: a recognition mechanism, which may be shared by other zinc finger TFs

biochemistry↗

bioRxiv2022

Methylation in NDUFA13 gene promoter disrupts communication between collaborative transcription factors - potential mechanism for onset of breast cancer.

Selective DNA binding by transcription factors (TFs) is crucial for the correct regulation of DNA transcription. In healthy cells, promoters of active genes are hypomethylated. A single CpG methylation within a TF response element may change the binding preferences of the protein thus causing the dysregulation of transcription programs. Here we investigate a molecular mechanism driving the downregulation of NDUFA13 gene, due to hypermethylation, which is associated with multiple cancers. Using bioinformatic analyses of breast cancer cell line MCF7, we identify a hypermethylated region containing the binding sites of two TFs dimers, CEBPB and E2F1-DP1, located 130 b.p. from the gene transcription start site. All-atom extended MD simulations of wild-type and methylated DNA alone and in complex with either one or both TFs dimers provide mechanistic insights into the cooperative asymmetric binding order of the two dimers; the CEBPB binding should occur first to facilitate the E2F1-DP1-DNA association. The CpG methylation within the E2F1-DP1 response element and the linker decreases the cooperativity effects and renders the E2F1-DP1 binding site less recognizable by the TF dimer. Taken together, the identified CpG methylation site may contribute to the downregulation of NDUFA13 gene and has a potential as a biomarker for breast cancer.

biochemistry↗

bioRxiv2022

Homologous BHLH transcription factors induce distinct deformations of torsionally-stressed DNA: a potential transcription regulation mechanism.

Changing torsional restraints on DNA is essential for the regulation of transcription. Torsional stress, introduced by RNA polymerase, can propagate along chromatin facilitating topological transitions and modulating the specific binding of transcription factors (TFs) to DNA. Despite the importance, the mechanistic details on how torsional stress impacts the TFs-DNA complexation remain scarce. Herein we address the impact of torsional stress on DNA complexation with homologous human basic-helix-loop-helix (BHLH) hetero- and homodimers: MycMax, MadMax, and MaxMax. The three TF dimers exhibit specificity towards the same DNA consensus sequences, the E-box response element, while regulating different transcriptional pathways. Using microseconds-long atomistic molecular dynamics simulations together with the torsional restraint that controls DNA total helical twist, we gradually over- and underwind naked and complexed DNA to a maximum of {+/-}5{degrees}/b.p. step. We observe that the binding of the BHLH dimers results in a similar increase in DNA torsional rigidity. However, under torsional stress the BHLH dimers induce distinct DNA deformations, characterised by changes in DNA grooves geometry and a significant asymmetric DNA bending. Supported by bioinformatics analyses, our data suggest that torsional stress may contribute to the execution of differential transcriptional programs of the homologous TFs by modulating their collaborative interactions.

biochemistry↗

bioRxiv2020

Sequence-specific dynamics of DNA response elements and their flanking sites regulate the recognition by AP-1 transcription factors

Activator proteins 1 (AP-1) comprise one of the largest families of eukaryotic basic leucine zipper transcription factors. Despite advances in the characterization of AP-1 DNA-binding sites, our ability to predict new binding sites and explain how the proteins achieve different gene expression levels remains limited. Here we address the role of sequence-specific DNA dynamics for stability and specific binding of AP-1 factors, using microseconds long molecular dynamics simulations. As a model system, we employ yeast AP-1 factor Yap1 binding to three different response elements from two genetic environments. Our data show that Yap1 actively exploits the sequence-specific plasticity of DNA within the response element to form stable protein-DNA complexes. The stability also depends on the four to six flanking nucleotides, adjacent to the response elements. The flanking sequences modulate the conformational adaptability of the response element, making it more shape-efficient to form specific contacts with the protein. Bioinformatics analysis of differential expression of the studied genes supports our conclusions: the stability of Yap1-DNA complexes, modulated by the flanking environment, influences the gene expression levels. Our results provide new insights into mechanisms of protein-DNA recognition and the biological regulation of gene expression levels in eukaryotes.

biochemistry↗

bioRxiv2019

BZIP Transcription Factors Modulate DNA Supercoiling Transitions

Torsional stress on DNA, introduced by molecular motors, constitutes an important regulatory mechanism of transcriptional control. Torsional stress can modulate specific binding of transcription factors to DNA and introduce local conformational changes that facilitate the opening of promoters and nucleosome remodeling. Using all-atom microsecond scale molecular dynamics simulations together with a torsional restraint that controls the total helical twist of a DNA fragment, we addressed the impact of torsional stress on DNA complexation with a human BZIP transcription factor, MafB. We gradually over- and underwind DNA alone and in complex with MafB by 5{degrees} per dinucleotide step, monitoring the evolution of the protein-DNA contacts at different degrees of torsional strain. Our computations show that MafB changes the DNA sequence-specific response to torsional stress. The dinucleotide steps that are susceptible to absorb most of the torsional stress become more torsionally rigid, as they are involved in the protein-DNA contacts. Also, the protein undergoes substantial conformational changes to follow the stress-induced DNA deformation, but mostly maintains the specific contacts with DNA. This results in a significant asymmetric increase of free energy of DNA twisting transitions, relative to free DNA, where overtwisting is more energetically unfavorable. Our data suggest that MafB could act as a torsional stress insulator, modulating the propagation of torsional stress along the chromatin fiber, which might promote cooperative binding of other transcription factors.

biochemistry↗