Nejvíce citovaný článek - PubMed ID 10736226
An A-type double helix of DNA having B-type puckering of the deoxyribose rings
The transition from B-DNA to A-DNA occurs in many protein-DNA interactions or in DNA/RNA hybrid duplexes, and thus plays a role in many important biomolecular processes that convey the biological function of DNA. However, the stability of A-DNA is severely underestimated in current AMBER force fields such as OL15, OL21 or bsc1, potentially leading to unstable or deformed protein-DNA complexes. In this study, we refine the deoxyribose dihedral potential to increase the stability of the north (N) puckering present in A-DNA. The new parameters, termed OL24, model A/B equilibrium in B-DNA duplexes in water in good agreement with nuclear magnetic resonance (NMR) experiment. They also improve the description of DNA/RNA hybrids and the transition of the DNA duplex to the A-form in concentrated ethanol solutions. These refinements significantly improve the modeling of protein-DNA complexes, increasing their structural stability and A-form population, while maintaining accurate representation of canonical B-DNA duplexes. Overall, the new parameters should allow more reliable modeling of the thermodynamic equilibrium between A- and B-DNA forms and the interactions of DNA with proteins.
Metal ions are essential components for the survival of living organisms. For most species, intracellular and extracellular ionic conditions differ significantly. As G-quadruplexes (G4s) are ion-dependent structures, changes in the [Na+]/[K+] ratio may affect the folding of genomic G4s. More than 11000 putative G4 sequences in the human genome (hg19) contain at least two runs of three continuous cytosines, and these mixed G/C-rich sequences may form a quadruplex or a competing hairpin structure based on G-C base pairing. In this study, we examine how the [Na+]/[K+] ratio influences the structures of G/C-rich sequences. The natural G4 structure with a 9-nt long central loop, CEBwt, was chosen as a model sequence, and the loop bases were gradually replaced by cytosines. The series of CEB mutations revealed that the presence of cytosines in G4 loops does not prevent G4 folding or decrease G4 stability but increases the probability of forming a competing structure, either a hairpin or an intermolecular duplex. Slow conversion to the quadruplex in vitro (in a potassium-rich buffer) and cells was demonstrated by NMR. 'Shape-shifting' sequences may respond to [Na+]/[K+] changes with delayed kinetics.
Non-canonical structures (NCS) refer to the various forms of DNA that differ from the B-conformation described by Watson and Crick. It has been found that these structures are usual components of the genome, actively participating in its essential functions. The present review is focused on the nine kinds of NCS appearing or likely to appear in human ribosomal DNA (rDNA): supercoiling structures, R-loops, G-quadruplexes, i-motifs, DNA triplexes, cruciform structures, DNA bubbles, and A and Z DNA conformations. We discuss the conditions of their generation, including their sequence specificity, distribution within the locus, dynamics, and beneficial and detrimental role in the cell.
- Klíčová slova
- DNA quadruplexes, Non-canonical DNA, R-loops, rDNA,
- MeSH
- G-kvadruplexy * MeSH
- konformace nukleové kyseliny MeSH
- lidé MeSH
- ribozomální DNA genetika MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
- Názvy látek
- ribozomální DNA MeSH
Here we review studies that provided important information about conformational properties of DNA using circular dichroic (CD) spectroscopy. The conformational properties include the B-family of structures, A-form, Z-form, guanine quadruplexes, cytosine quadruplexes, triplexes and other less characterized structures. CD spectroscopy is extremely sensitive and relatively inexpensive. This fast and simple method can be used at low- as well as high-DNA concentrations and with short- as well as long-DNA molecules. The samples can easily be titrated with various agents to cause conformational isomerizations of DNA. The course of detected CD spectral changes makes possible to distinguish between gradual changes within a single DNA conformation and cooperative isomerizations between discrete structural states. It enables measuring kinetics of the appearance of particular conformers and determination of their thermodynamic parameters. In careful hands, CD spectroscopy is a valuable tool for mapping conformational properties of particular DNA molecules. Due to its numerous advantages, CD spectroscopy significantly participated in all basic conformational findings on DNA.
- MeSH
- A-DNA chemie MeSH
- cirkulární dichroismus * MeSH
- denaturace nukleových kyselin MeSH
- DNA chemie MeSH
- G-kvadruplexy MeSH
- konformace nukleové kyseliny MeSH
- Z-DNA chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
- Názvy látek
- A-DNA MeSH
- DNA MeSH
- triplex DNA MeSH Prohlížeč
- Z-DNA MeSH
A simple method is presented to monitor conformational isomerizations along genomic DNA. We illustrate properties of the method with the B-A conformational transition induced by ethanol in linearized pUC19 plasmid DNA. At various ethanol concentrations, the DNA was irradiated with ultraviolet light, transferred to a restriction endonuclease buffer and the irradiated DNA was cleaved by 17 restriction endonucleases. The irradiation damaged DNA and the damage blocked the restrictase cleavage. The amount of uncleaved, i.e. damaged, DNA depended on the concentration of ethanol in a characteristic S-shape way typical of the cooperative B-A transition. The transition beginning and midpoint were determined for each restriction endonuclease. These data map the B-A transition along the whole polylinker of pUC19 DNA and six evenly distributed recognition sequences within the rest of the plasmid. The transition midpoints fell within the B-A transition region of the plasmid simultaneously determined by CD spectroscopy. The present method complements the previous methods used to study the B-A transition. It can be employed to analyze multikilobase regions of genomic DNA whose restriction endonuclease cleavage fragments can be separated and quantified on agarose gels.
- MeSH
- A-DNA chemie účinky záření MeSH
- cesium farmakologie MeSH
- cirkulární dichroismus * MeSH
- DNA chemie účinky záření MeSH
- konformace nukleové kyseliny účinky léků MeSH
- plazmidy chemie účinky záření MeSH
- restrikční enzymy metabolismus MeSH
- ultrafialové záření MeSH
- Publikační typ
- časopisecké články MeSH
- hodnotící studie MeSH
- práce podpořená grantem MeSH
- Názvy látek
- A-DNA MeSH
- cesium MeSH
- DNA MeSH
- restrikční enzymy MeSH
The formation of a cation-stabilized guanine quadruplex (G-DNA) stem is an exceptionally slow process involving complex kinetics that has not yet been characterized at atomic resolution. Here, we investigate the formation of a parallel stranded G-DNA stem consisting of four strands of d(GGGG) using molecular dynamics simulations with explicit inclusion of counterions and solvent. Due to the limitations imposed by the nanosecond timescale of the simulations, rather than watching for the spontaneous formation of G-DNA, our approach probes the stability of possible supramolecular intermediates (including two-, three-, and four-stranded assemblies with out-of-register base pairing between guanines) on the formation pathway. The simulations suggest that "cross-like" two-stranded assemblies may serve as nucleation centers in the initial formation of parallel stranded G-DNA quadruplexes, proceeding through a series of rearrangements involving trapping of cations, association of additional strands, and progressive slippage of strands toward the full stem. To supplement the analysis, approximate free energies of the models are obtained with explicit consideration of the integral cations. The approach applied here serves as a prototype for qualitatively investigating other G-DNA molecules using molecular dynamics simulation and free-energy analysis.
- MeSH
- časové faktory MeSH
- DNA chemie MeSH
- G-kvadruplexy MeSH
- guanin chemie MeSH
- ionty MeSH
- kationty MeSH
- kinetika MeSH
- konformace nukleové kyseliny MeSH
- molekulární konformace MeSH
- molekulární modely MeSH
- oligonukleotidy chemie MeSH
- sodík chemie MeSH
- software MeSH
- teplota MeSH
- termodynamika MeSH
- vodíková vazba MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Názvy látek
- DNA MeSH
- guanin MeSH
- ionty MeSH
- kationty MeSH
- oligonukleotidy MeSH
- sodík MeSH
MULDER (Mostly UniversaL Dihedral angle ExtractoR) is a program for extraction of torsion angle information from NMR data. Currently, it can analyze two types of input data: The torsion angle data, where several (3)J-coupling constants and/or interatomic distances are combined in order to reduce the torsion angle ambiguity arising from solving the isolated Karplus (or distance) equation, and the sugar pucker data, where the dynamics of five-membered sugar rings is evaluated by postprocessing the results calculated from (3)J((HH)) coupling constants by program PSEUROT. Program MULDER can be used either as an alternative to r-MD programs in situations where only specific structural features are studied, or as a preparatory tool in connection with full r-MD structure calculation for extraction of unambiguous torsion angle restraints.
Unrestrained 5-20-ns explicit-solvent molecular dynamics simulations using the Cornell et al. force field have been carried out for d[GCG(N)11GCG]2 (N, purine base) considering guanine*cytosine (G*C), adenine*thymine (A*T), inosine*5-methyl-cytosine (I*mC), and 2-amino-adenine*thymine (D*T) basepairs. The simulations unambiguously show that the structure and elasticity of N-tracts is primarily determined by the presence of the amino group in the minor groove. Simulated A-, I-, and AI-tracts show almost identical structures, with high propeller twist and minor groove narrowing. G- and D-tracts have small propeller twisting and are partly shifted toward the A-form. The elastic properties also differ between the two groups. The sequence-dependent electrostatic component of base stacking seems to play a minor role. Our conclusions are entirely consistent with available experimental data. Nevertheless, the propeller twist and helical twist in the simulated A-tract appear to be underestimated compared to crystallographic studies. To obtain further insight into the possible force field deficiencies, additional multiple simulations have been made for d(A)10, systematically comparing four major force fields currently used in DNA simulations and utilizing B and A-DNA forms as the starting structure. This comparison shows that the conclusions of the present work are not influenced by the force field choice.
- MeSH
- DNA chemie MeSH
- konformace nukleové kyseliny MeSH
- molekulární modely MeSH
- párování bází MeSH
- polydeoxyribonukleotidy chemie MeSH
- pružnost MeSH
- puriny chemie MeSH
- vodíková vazba MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- DNA MeSH
- polydeoxyribonukleotidy MeSH
- puriny MeSH
The ability of the four-stranded guanine (G)-DNA motif to incorporate nonstandard guanine analogue bases 6-oxopurine (inosine, I), 6-thioguanine (tG), and 6-thiopurine (tI) has been investigated using large-scale molecular dynamics simulations. The simulations suggest that a G-DNA stem can incorporate inosines without any marked effect on its structure and dynamics. The all-inosine quadruplex stem d(IIII)(4) shows identical dynamical properties as d(GGGG)(4) on the nanosecond time scale, with both molecular assemblies being stabilized by monovalent cations residing in the channel of the stem. However, simulations carried out in the absence of these cations show dramatic differences in the behavior of d(GGGG)(4) and d(IIII)(4). Whereas vacant d(GGGG)(4) shows large fluctuations but does not disintegrate, vacant d(IIII)(4) is completely disrupted within the first nanosecond. This is a consequence of the lack of the H-bonds involving the N2 amino group that is not present in inosine. This indicates that formation of the inosine quadruplex could involve entirely different intermediate structures than formation of the guanosine quadruplex, and early association of cations in this process appears to be inevitable. In the simulations, the incorporation of 6-thioguanine and 6-thiopurine sharply destabilizes four-stranded G-DNA structures, in close agreement with experimental data. The main reason is the size of the thiogroup leading to considerable steric conflicts and expelling the cations out of the channel of the quadruplex stem. The G-DNA stem can accommodate a single thioguanine base with minor perturbations. Incorporation of a thioguanine quartet layer is associated with a large destabilization of the G-DNA stem whereas the all-thioguanine quadruplex immediately collapses.
- MeSH
- biofyzika MeSH
- biofyzikální jevy MeSH
- DNA chemie MeSH
- inosin chemie MeSH
- iontové kanály chemie MeSH
- konformace nukleové kyseliny * MeSH
- merkaptopurin chemie MeSH
- molekulární modely MeSH
- sodík chemie MeSH
- termodynamika MeSH
- thioguanin chemie MeSH
- vodíková vazba MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- DNA MeSH
- inosin MeSH
- iontové kanály MeSH
- merkaptopurin MeSH
- sodík MeSH
- thioguanin MeSH
The crystal structure of d(CATGGGCCCATG)(2) shows unique stacking patterns of a stable B<-->A-DNA intermediate. We evaluated intrinsic base stacking energies in this crystal structure using an ab initio quantum mechanical method. We found that all crystal base pair steps have stacking energies close to their values in the standard and crystal B-DNA geometries. Thus, naturally occurring stacking geometries were essentially isoenergetic while individual base pair steps differed substantially in the balance of intra-strand and inter-strand stacking terms. Also, relative dispersion, electrostatic and polarization contributions to the stability of different base pair steps were very sensitive to base composition and sequence context. A large stacking flexibility is most apparent for the CpA step, while the GpG step is characterized by weak intra-strand stacking. Hydration effects were estimated using the Langevin dipoles solvation model. These calculations showed that an aqueous environment efficiently compensates for electrostatic stacking contributions. Finally, we have carried out explicit solvent molecular dynamics simulation of the d(CATGGGCCCATG)(2) duplex in water. Here the DNA conformation did not retain the initial crystal geometry, but moved from the B<-->A intermediate towards the B-DNA structure. The base stacking energy improved in the course of this simulation. Our findings indicate that intrinsic base stacking interactions are not sufficient to stabilize the local conformational variations in crystals.
- MeSH
- DNA chemie genetika metabolismus MeSH
- krystalizace MeSH
- molekulární modely MeSH
- ohebnost (fyzika) MeSH
- párování bází * MeSH
- počítačová simulace * MeSH
- rozpouštědla MeSH
- sekvence nukleotidů MeSH
- statická elektřina MeSH
- termodynamika MeSH
- voda chemie metabolismus MeSH
- zastoupení bazí MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- DNA MeSH
- rozpouštědla MeSH
- voda MeSH
