quadruplex
Dotaz
Zobrazit nápovědu
Four-stranded DNA structures were structurally characterized in vitro by NMR, X-ray and Circular Dichroism spectroscopy in detail. Among the different types of quadruplexes (i-Motifs, minor groove quadruplexes, G-quadruplexes, etc.), the best described are G-quadruplexes which are featured by Hoogsteen base-paring. Sequences with the potential to form quadruplexes are widely present in genome of all organisms. They are found often in repetitive sequences such as telomeric ones, and also in promoter regions and 5' non-coding sequences. Recently, many proteins with binding affinity to G-quadruplexes have been identified. One of the initially portrayed G-rich regions, the human telomeric sequence (TTAGGG)n, is recognized by many proteins which can modulate telomerase activity. Sequences with the potential to form G-quadruplexes are often located in promoter regions of various oncogenes. The NHE III1 region of the c-MYC promoter has been shown to interact with nucleolin protein as well as other G-quadruplex-binding proteins. A number of G-rich sequences are also present in promoter region of estrogen receptor alpha. In addition to DNA quadruplexes, RNA quadruplexes, which are critical in translational regulation, have also been predicted and observed. For example, the RNA quadruplex formation in telomere-repeat-containing RNA is involved in interaction with TRF2 (telomere repeat binding factor 2) and plays key role in telomere regulation. All these fundamental examples suggest the importance of quadruplex structures in cell processes and their understanding may provide better insight into aging and disease development.
- MeSH
- DNA vazebné proteiny chemie metabolismus MeSH
- DNA chemie metabolismus MeSH
- G-kvadruplexy * MeSH
- konformace nukleové kyseliny MeSH
- lidé MeSH
- promotorové oblasti (genetika) MeSH
- RNA chemie metabolismus MeSH
- stárnutí MeSH
- telomery MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
Guanine-quadruplex structures (G4) are unusual nucleic acid conformations formed by guanine-rich DNA and RNA sequences and known to control gene expression mechanisms, from transcription to protein synthesis. So far, a number of molecules that recognize G4 have been developed for potential therapeutic applications in human pathologies, including cancer and infectious diseases. These molecules are called G4 ligands. When the biological effects of G4 ligands are studied, the analysis is often limited to nucleic acid targets. However, recent evidence indicates that G4 ligands may target other cellular components and compartments such as lysosomes and mitochondria. Here, we summarize our current knowledge of the regulation of lysosome by G4 ligands, underlying their potential functional impact on lysosome biology and autophagic flux, as well as on the transcriptional regulation of lysosomal genes. We outline the consequences of these effects on cell fate decisions and we systematically analyzed G4-prone sequences within the promoter of 435 lysosome-related genes. Finally, we propose some hypotheses about the mechanisms involved in the regulation of lysosomes by G4 ligands.
- MeSH
- autofagie * MeSH
- DNA metabolismus MeSH
- G-kvadruplexy * MeSH
- guanin MeSH
- lidé MeSH
- ligandy MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
G-quadruplexes are noncanonical nucleic acid structures formed by stacked guanine tetrads. They are capable of a range of functions and thought to play widespread biological roles. This diversity raises an important question: what determines the biochemical specificity of G-quadruplex structures? The answer is particularly important from the perspective of biological regulation because genomes can contain hundreds of thousands of G-quadruplexes with a range of functions. Here we analyze the specificity of each sequence in a 496-member library of variants of a reference G-quadruplex with respect to five functions. Our analysis shows that the sequence requirements of G-quadruplexes with these functions are different from one another, with some mutations altering biochemical specificity by orders of magnitude. Mutations in tetrads have larger effects than mutations in loops, and changes in specificity are correlated with changes in multimeric state. To complement our biochemical data we determined the solution structure of a monomeric G-quadruplex from the library. The stacked and accessible tetrads rationalize why monomers tend to promote a model peroxidase reaction and generate fluorescence. Our experiments support a model in which the sequence requirements of G-quadruplexes with different functions are overlapping but distinct. This has implications for biological regulation, bioinformatics, and drug design.
MOTIVATION: Expanding research highlights the importance of guanine quadruplex structures. Therefore, easy-accessible tools for quadruplex analyses in DNA and RNA molecules are important for the scientific community. RESULTS: We developed a web version of the G4Hunter application. This new web-based server is a platform-independent and user-friendly application for quadruplex analyses. It allows retrieval of gene/nucleotide sequence entries from NCBI databases and provides complete characterization of localization and quadruplex propensity of quadruplex-forming sequences. The G4Hunter web application includes an interactive graphical data representation with many useful options including visualization, sorting, data storage and export. AVAILABILITY AND IMPLEMENTATION: G4Hunter web application can be accessed at: http://bioinformatics.ibp.cz. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.
- MeSH
- DNA MeSH
- G-kvadruplexy * MeSH
- guanin MeSH
- internet MeSH
- počítače MeSH
- sekvenční analýza DNA MeSH
- software MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
MOTIVATION: G-quadruplex is a DNA or RNA form in which four guanine-rich regions are held together by base pairing between guanine nucleotides in coordination with potassium ions. G-quadruplexes are increasingly seen as a biologically important component of genomes. Their detection in vivo is problematic; however, sequencing and spectrometric techniques exist for their in vitro detection. We previously devised the pqsfinder algorithm for PQS identification, implemented it in C++ and published as an R/Bioconductor package. We looked for ways to optimize pqsfinder for faster and user-friendly sequence analysis. RESULTS: We identified two weak points where pqsfinder could be optimized. We modified the internals of the recursive algorithm to avoid matching and scoring many sub-optimal PQS conformations that are later discarded. To accommodate the needs of a broader range of users, we created a website for submission of sequence analysis jobs that does not require knowledge of R to use pqsfinder. AVAILABILITY AND IMPLEMENTATION: https://pqsfinder.fi.muni.cz, https://bioconductor.org/packages/pqsfinder. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.
- MeSH
- algoritmy MeSH
- G-kvadruplexy * MeSH
- genom MeSH
- RNA MeSH
- software MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
G-quadruplexes are non-B secondary structures with regulatory functions and therapeutic potential. Improvements in sequencing methods recently allowed the completion of the first human chromosome which is now available as a gapless, end-to-end assembly, with the previously remaining spaces filled and newly identified regions added. We compared the presence of G-quadruplex forming sequences in the current human reference genome (GRCh38) and in the new end-to-end assembly of the X chromosome constructed by high-coverage ultra-long-read nanopore sequencing. This comparison revealed that, even though the corrected length of the chromosome X assembly is surprisingly 1.14% shorter than expected, the number of G-quadruplex forming sequences found in this gapless chromosome is significantly higher, with 493 new motifs having G4Hunter scores above 1.4 and 23 new sequences with G4Hunter scores above 3.5. This observation reflects an improved precision of the new sequencing approaches and points to an underestimation of G-quadruplex propensity in the previous, widely used version of the human genome assembly, especially for motifs with a high G4Hunter score, expected to be very stable. These G-quadruplex forming sequences probably remained undiscovered in earlier genome datasets due to previously unsolved G-rich and repetitive genomic regions. These observations allow a precise targeting of these important regulatory regions.
- MeSH
- G-kvadruplexy * MeSH
- lidé MeSH
- lidské chromozomy X chemie genetika MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
The 22-mer c-kit promoter sequence folds into a parallel-stranded quadruplex with a unique structure, which has been elucidated by crystallographic and NMR methods and shows a high degree of structural conservation. We have carried out a series of extended (up to 10 μs long, ∼50 μs in total) molecular dynamics simulations to explore conformational stability and loop dynamics of this quadruplex. Unfolding no-salt simulations are consistent with a multi-pathway model of quadruplex folding and identify the single-nucleotide propeller loops as the most fragile part of the quadruplex. Thus, formation of propeller loops represents a peculiar atomistic aspect of quadruplex folding. Unbiased simulations reveal μs-scale transitions in the loops, which emphasizes the need for extended simulations in studies of quadruplex loops. We identify ion binding in the loops which may contribute to quadruplex stability. The long lateral-propeller loop is internally very stable but extensively fluctuates as a rigid entity. It creates a size-adaptable cleft between the loop and the stem, which can facilitate ligand binding. The stability gain by forming the internal network of GA base pairs and stacks of this loop may be dictating which of the many possible quadruplex topologies is observed in the ground state by this promoter quadruplex.
- MeSH
- denaturace nukleových kyselin MeSH
- draslík chemie MeSH
- G-kvadruplexy * MeSH
- kationty MeSH
- párování bází MeSH
- promotorové oblasti (genetika) * MeSH
- protoonkogenní proteiny c-kit genetika MeSH
- simulace molekulární dynamiky MeSH
- sodík chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Quadruplexes are noncanonical DNA structures that arise in guanine rich loci and have important biological functions. Classically, quadruplexes contain four stacked intramolecular G-tetrads. Surprisingly, although some algorithms allow searching for longer than 4G tracts for quadruplex formation, these have not yet been systematically studied. Therefore, we analyzed the human genome for sequences that are predicted to adopt stacked intramolecular G-tetrads with greater than four stacks. The data provide evidence for numerous G-quadruplexes that contain five or six stacked intramolecular G-tetrads. These sequences are predominantly found in known gene regulatory regions. Electrophoretic mobility assays and circular dichroism spectroscopy indicate that these sequences form quadruplex structures in vitro under physiological conditions. The localization and in vitro stability of these G-quadruplexes indicate their potentially important roles in gene regulation and their potential for therapeutic applications.
The structures of DNA G-quadruplexes are essential for their functions in vivo and in vitro. Our present study revealed that sequential order of the three G-quadruplex loops, that is, loop transposition, could be a critical factor to determinate the G-quadruplex conformation and consequently improved the catalytic function of G-quadruplex based DNAzyme. In the presence of 100mM K+, loop transposition induced one of the G-quadruplex isomers which shared identical loops but differed in the sequential order of loops into a hybrid topology while the others into predominately parallel topologies. 1D NMR spectroscopy and mutation analysis suggested that the hydrogen bonding from loops residues with nucleotides in flanking sequences may be responsible for the stabilization of the different conformations. A well-known DNAzyme consisting of G-quadruplex and hemin (Ferriprotoporphyrin IX chloride) was chosen to test the catalytic function. We found that the loop transposition could enhance the reaction rate obviously by increasing the hemin binding affinity to G-quadruplex. These findings disclose the relations between the loop transposition, G-quadruplex conformation and catalytic function of DNAzyme.
DNA concentration has been recently suggested to be the reason why different arrangements are revealed for K(+)-stabilized human telomere quadruplexes by experimental methods requiring DNA concentrations differing by orders of magnitude. As Raman spectroscopy can be applied to DNA samples ranging from those accessible by absorption and CD spectroscopies up to extremely concentrated solutions, gels and even crystals; it has been used here to clarify polymorphism of a core human telomeric sequence G(3)(TTAG(3))(3) in the presence of K(+) and Na(+) ions throughout wide range of DNA concentrations. We demonstrate that the K(+)-structure of G(3)(TTAG(3))(3) at low DNA concentration is close to the antiparallel fold of Na(+)-stabilized quadruplex. On the increase of G(3)(TTAG(3))(3) concentration, a gradual transition from antiparallel to intramolecular parallel arrangement was observed, but only for thermodynamically equilibrated K(+)-stabilized samples. The transition is synergically supported by increased K(+) concentration. However, even for extremely high G(3)(TTAG(3))(3) and K(+) concentrations, an intramolecular antiparallel quadruplex is spontaneously formed from desalted non-quadruplex single-strand after addition of K(+) ions. Thermal destabilization or long dwell time are necessary to induce interquadruplex transition. On the contrary, Na(+)-stabilized G(3)(TTAG(3))(3) retains its antiparallel folding regardless of the extremely high DNA and/or Na(+) concentrations, thermal destabilization or annealing.
