Localization of some molecules within the grooves of DNA by modification of their complexes with dimethyl sulphate

The comparative methylation with [³H] dimethyl sulphate (DMS) of free DNA and DNA in chromatin and nuclei within the minor and major grooves of the DNA double helix and its single stranded regions was measured.The results suggest that histones lie partly inside the major groove and partly out of the grooves of DNA in chromatin leaving the minor groove open; most of the non-histone proteins of chromatin are not buried in the DNA grooves; the content of single stranded DNA in chromatin does not exceed 0.5%.     

A study of unwinding of DNA and shielding of the DNA grooves by RNA polymerase by using methylation with dimethylsulphate.

The dimethylsulphate method has been used to study the complexes of RNA polymerase (Escherichia coli) with DNA of T7 phage, poly[d(A--T)] and fragments of calf thymus DNA protected against DNase digestion by RNA polymerase. The binding of RNA polymerase to DNA significantly increases the formation of 1-methyl-adenine produced by methylation of the single-stranded DNA region, diminishes by about 10% the formation of 3-methyl-adenine by methylation within the minor groove and does not affect the formation of 7-methyl-guanine by methylation within the major DNA groove. The presence of nascent RNA decreases the formation of 1-methyl-adenine in DNA of the complex by about 30%. The initiation of RNA synthesis or RNA synthesis itself does not influence the methylation of the major groove but shielding of the minor groove increases by about twice as much. These results suggest that RNA polymerase, upon binding, breaks Watson-Crick base-pairing in a DNA region of about 15-base-pairs long, that nascent RNA forms a duplex with DNA of about 10-base-pairs long; and that the enzyme weakly interacts with DNA along its grooves and preferentially makes contacts with the minor groove.     

Understanding the sequence-dependence of DNA groove dimensions: implications for DNA interactions

Background

The B-DNA major and minor groove dimensions are crucial for DNA-protein interactions. It has long been thought that the groove dimensions depend on the DNA sequence, however this relationship has remained elusive. Here, our aim is to elucidate how the DNA sequence intrinsically shapes the grooves.

Methodology/Principal Findings

The present study is based on the analysis of datasets of free and protein-bound DNA crystal structures, and from a compilation of NMR ³¹P chemical shifts measured on free DNA in solution on a broad range of representative sequences. The ³¹P chemical shifts can be interpreted in terms of the BI↔BII backbone conformations and dynamics. The grooves width and depth of free and protein-bound DNA are found to be clearly related to the BI/BII backbone conformational states. The DNA propensity to undergo BI↔BII backbone transitions is highly sequence-dependent and can be quantified at the dinucleotide level. This dual relationship, between DNA sequence and backbone behavior on one hand, and backbone behavior and groove dimensions on the other hand, allows to decipher the link between DNA sequence and groove dimensions. It also firmly establishes that proteins take advantage of the intrinsic DNA groove properties.

Conclusions/Significance

The study provides a general framework explaining how the DNA sequence shapes the groove dimensions in free and protein-bound DNA, with far-reaching implications for DNA-protein indirect readout in both specific and non specific interactions.     

Binding Sites of the Polyamines Putrescine,Cadaverine, Spermidine and Spermine on A- and B-DNA Located by Simulated Annealing

Abstract

Molecular dynamics simulations with simulated annealing are performed on polyamine-DNA systems in order to determine the binding sites of putrescine, cadaverine, spermidine and spermine on A- and B-DNA. The simulations either contain no additional counterions or sufficient Na⁺ ions, together with the charge on the polyamine, to provide 73% neutralisation of the charges on the DNA phosphates. The stabilisation energies of the complexes indicate that all four polyamines should stabilise A-DNA in preference to B-DNA, which is in agreement with experiment in the case of spermine and spermidine, but not in the case of putrescine or cadaverine. The major groove is the preferred binding site on A-DNA of all the polyamines. Putrescine and cadaverine tend to bind to the sugar-phosphate backbone of B-DNA, whereas spermidine and spermine occupy more varied sites, including binding along the backbone and bridging both the major and minor grooves.     

Molecular dynamics simulations and binding free energy analysis of DNA minor groove complexes of curcumin

Curcumin is a natural phytochemical that exhibits a wide range of pharmacological properties, including antitumor and anticancer activities. The similarity in the shape of curcumin to DNA minor groove binding drugs is the motivation for exploring its binding affinity in the minor grooves of DNA sequences. Interactions of curcumin with DNA have not been extensively examined, while its pharmacological activities have been studied and documented in depth. Curcumin was docked with two DNA duplexes, d(GTATATAC)₂ and d(CGCGATATCGCG)₂, and molecular dynamics simulations of the complexes were performed in explicit solvent to determine the stability of the binding. In all systems, the curcumin is positioned in the minor groove in the A·T region, and was stably bound throughout the simulation, causing only minor modifications to the structural parameters of DNA. Water molecules were found to contribute to the stability of the binding of the ligand. Free energy analyses of the complexes were performed with MM-PBSA, and the binding affinities that were calculated are comparable to the values reported for other similar nucleic acid–ligand systems, indicating that curcumin is a suitable natural molecule for the development of minor groove binding drugs.     

Alteration of the groove width of DNA induced by the multimodal hydrogen bonding of denaturants with DNA bases in its grooves affects their stability

BackgroundDenaturants, namely, urea and guanidinium chloride (GdmCl) affect the stability as well as structure of DNA. Critical assessment of the role of hydrogen bonding of these denaturants with the different regions of DNA is essential in terms of its stability and structural aspect. However, the understanding of the mechanistic aspects of structural change of DNA induced by the denaturants is not yet well understood.MethodsIn this study, various spectroscopic along with molecular dynamics (MD) simulation techniques were employed to understand the role of hydrogen bonding of these denaturants with DNA bases in their stability and structural change.Results and conclusionIt has been found that both, GdmCl and urea intrude into groove region of DNA by striping surrounding water. The hydrogen bonding pattern of Gdm⁺ and urea with DNA bases in its groove region is multimodal and distinctly different from each other. The interaction of GdmCl with DNA is stabilized by electrostatic interaction whereas electrostatic and Lennard-Jones interactions both contribute for urea. Gdm⁺ forms direct hydrogen bond with the bases in the minor groove of DNA whereas direct and water assisted hydrogen bond takes place with urea. The hydrogen bond formed between Gdm⁺ with bases in the groove region of DNA is stronger than urea due to strong electrostatic interaction along with less self-aggregation of Gdm⁺ than urea. The distinct hydrogen bonding capability of Gdm⁺ and urea with DNA bases in its groove region affects its width differently. The interaction of Gdm⁺ decreases the width of the minor and major groove which probably increases the strength of hydrogen bond between the Watson-Crick base pairs of DNA leading to its stability. In contrast, the interaction of urea does not affect much to the width of the grooves except the marginal increase in the minor groove width which probably decreases the strength of hydrogen bond between Watson Crick base pairs leading to the destabilization of DNA.General significanceOur study clearly depicts the role of hydrogen bonding between DNA bases and denaturants in their stability and structural change which can be used further for designing of the guanidinium based drug molecules.     

A Study of the Interaction of Cr(III) Complexes and Their Selective Binding with B-DNA: A Molecular Modeling Approach

Abstract

Molecular modeling and energy minimisation calculations have been used to investigate the interaction of chromium(III) complexes in different ligand environments with various sequences of B-DNA. The complexes are [Cr(salen)(H₂O)₂]⁺; salen denotes 1, 2 bis-salicylideneaminoethane, [Cr(salprn)(H₂O)₂]⁺; salprn denotes 1, 3 bis- salicylideneamino-propane, [Cr(phen)₃]³⁺; phen denotes 1, 10 phenanthroline and [Cr(en)₃]³⁺; en denotes eth- ylenediamine. All the chromium(III) complexes are interacted with the minor groove and major groove of d(AT)₁₂, d(CGCGAATTCGCG)₂ and d(GC)₁₂ sequences of DNA. The binding energy and hydrogen bond parameters of DNA-Cr complex adduct in both the groove have been determined using molecular mechanics approach. The binding energy and formation of hydrogen bonds between chromium(III) complex and DNA has shown that all complexes of chromium(III) prefer minor groove interaction as the favourable binding mode.     

An electrostatic model for the dielectric effects,the adsorption of multivalent ions,and the bending of B-DNA

We have studied electrostatic properties of DNA with a discrete charge model consisting of a cylindrical dielectric core with a radius of 8 Å and a dielectric constant D_i = 4, surrounded by two helical strings of phosphate point charges at 10 Å from the axis, immersed in an aqueous medium with dielectric constant D_w = 78.54. Eliminating the dielectric core makes potentials in the phosphate surface less negative by about 0.5 kT/e. Salt effects are evaluated for the model without a dielectric core, using the shielded Coulomb potential. Smearing the phosphate charges increases their potential by about 2.5 kT/e, due mostly to the self-potential of the smeared charge. Potentials in the center of the minor and major grooves vary less than 0.02 kT/e along their helical path. The potential in the center of the minor groove is from 1.0 to 1.7 kT/e, more negative than in the center of the major groove, depending on dielectric core and salt concentration. So multivalent cations and also larger cationic ligands, such as some antibiotics, are likely to adsorb in the minor groove, in agreement with earlier computations by A. and B. Pullman. Dielectric effects on the surface potential and the local potential variations are found to be relatively small. Bending of DNA is studied by placing a multivalent cation, M^Z+, in the center of the minor or major groove, curving DNA around it for a certain length, and calculating the free energy difference between the bent and the straight configuration. Boltzmann averaged bending angles, 〈β〉, are found to be maximal in 0.03M monovalent salt, for a length of about 50 or 25 Å of curved DNA when an M^Z+ ion is adsorbed in the minor or the major groove, respectively. When the dielectric constant of water is used throughout the calculation, we find maximal bends of 〈β〉 = 11° for M²⁺ and 〈β〉 = 16° for M³⁺ in the minor groove, 〈β〉 = 13° for M³⁺ in the major groove. The absence of bends in DNA adsorbed to mica in the presence of Mg salts supports the role of Mg²⁺ in “ion bridging” between DNA and mica. The treatment of the effective dielectric constant between two points outside a dielectric cylinder in water is appended. © 1998 John Wiley & Sons, Inc. Biopoly 46: 503–516, 1998     

Similarities and differences in interaction of K+ and Na+ with condensed ordered DNA. A molecular dynamics computer simulation study

Four 20 ns molecular dynamics simulations have been performed with two counterions, K⁺ or Na⁺, at two water contents, 15 or 20 H₂O per nucleotide. A hexagonal simulation cell comprised of three identical DNA decamers [d(5′-ATGCAGTCAG) × d(5′-TGACTGCATC)] with periodic boundary condition along the DNA helix was used. The simulation setup mimics the DNA state in oriented DNA fibers or in crystals of DNA oligomers. Variation of counterion nature and water content do not alter averaged DNA structure. K⁺ and Na⁺ binding to DNA are different. K⁺ binds to the electronegative sites of DNA bases in the major and the minor grooves, while Na⁺ interacts preferentially with the phosphate groups. Increase of water causes a shift of both K⁺ and Na⁺ from the first hydration shell of O1P/O2P and of the DNA bases in the minor groove with lesser influence for the cation binding to the bases in the major groove. Mobility of both water and cations in the K–DNA systems is faster than in the Na–DNA systems: Na⁺ organizes and immobilizes water structure around itself and near DNA while for K⁺ water is less organized and more dynamic.     

Discrimination against major groove adducts by Y-family polymerases of the DinB subfamily

Y-family DNA polymerases bypass DNA adducts in a process known as translesion synthesis (TLS). Y-family polymerases make contacts with the minor groove side of the DNA substrate at the nascent base pair. The Y-family polymerases also contact the DNA major groove via the unique little finger domain, but they generally lack contacts with the major groove at the nascent base pair. Escherichia coli DinB efficiently and accurately copies certain minor groove guanosine adducts. In contrast, we previously showed that the presence in the DNA template of the major groove-modified base 1,3-diaza-2-oxophenothiazine (tC) inhibits the activity of E. coli DinB. Even when the DNA primer is extended up to three nucleotides beyond the site of the tC analog, DinB activity is strongly inhibited. These findings prompted us to investigate discrimination against other major groove modifications by DinB and its orthologs. We chose a set of pyrimidines and purines with modifications in the major groove and determined the activity of DinB and several orthologs with these substrates. DinB, human pol kappa, and Sulfolobus solfataricus Dpo4 show differing specificities for the major groove adducts pyrrolo-dC, dP, N⁶-furfuryl-dA, and etheno-dA. In general, DinB was least efficient for bypass of all of these major groove adducts, whereas Dpo4 was most efficient. DinB activity was essentially completely inhibited by the presence of etheno-dA, while pol kappa activity was strongly inhibited. All three of these DNA polymerases were able to bypass N⁶-furfuryl-dA with modest efficiency, with DinB being the least efficient. We also determined that the R35A variant of DinB enhances bypass of N⁶-furfuryl-dA but not etheno-dA. In sum, we find that whereas DinB is specific for bypass of minor groove adducts, it is specifically inhibited by major groove DNA modifications.     

What drives proteins into the major or minor grooves of DNA?

The energetic profiles of a significant number of protein-DNA systems at 20 °C reveal that, despite comparable Gibbs free energies, association with the major groove is primarily an enthalpy-driven process, whereas binding to the minor groove is characterized by an unfavorable enthalpy that is compensated by favorable entropic contributions. These distinct energetic signatures for major versus minor groove binding are irrespective of the magnitude of DNA bending and/or the extent of binding-induced protein refolding. The primary determinants of their different energetic profiles appear to be the distinct hydration properties of the major and minor grooves; namely, that the water in the A+T-rich minor groove is in a highly ordered state and its removal results in a substantial positive contribution to the binding entropy. Since the entropic forces driving protein binding into the minor groove are a consequence of displacing water ordered by the regular arrangement of polar contacts, they cannot be regarded as hydrophobic.     

Distamycin-stabilized Antiparallel-Parallel Combination (APC) DNA

Abstract

The formation of Antiparallel-Parallel-Combination (APC) DNA, a liner duplex with a segment of parallel-stranded (ps) helix flanked by conventional B-DNA, was tested with a number of synthetic oligonucleotides. The groove-binding ligand distamycin A (DstA) was used to stabilize the ps segment comprising five A·T base pairs. Two drug molecules bound per APC, one in each of the two equivalent grooves characteristic of ps-DNA. APC-DNA, reference molecules and their complexes with DstA were analysed by several methods: circular dichroism and absorption spectroscopy, thermal denaturation, chemical modification, and molecular modeling. The dye binding stoichiometry differed significantly due to inherent structural differences in the groove geometries of ps-DNA (trans base pairs, similar grooves) and conventional antiparallel-stranded (aps) B-DNA (cis base pairs, distinct major and minor grooves). The data support the existence of APC folding in solution.     

Cooperative stabilization of Zn2+:DNA complexes through netropsin binding in the minor groove of FdU-substituted DNA

The simultaneous binding of netropsin in the minor groove and Zn²⁺ in the major groove of a DNA hairpin that includes 10 consecutive FdU nucleotides at the 3′-terminus (3′FdU) was demonstrated based upon NMR spectroscopy, circular dichroism (CD), and computational modeling studies. The resulting Zn²⁺/netropsin: 3′FdU complex had very high thermal stability with aspects of the complex intact at 85?°C, conditions that result in complete dissociation of Mg²⁺ complexes. CD and ¹⁹F NMR spectroscopy were consistent with Zn²⁺ binding in the major groove of the DNA duplex and utilizing F5 and O4 of consecutive FdU nucleotides as ligands with FdU nucleotides hemi-deprotonated in the complex. Netropsin is bound in the minor groove of the DNA duplex based upon 2D NOESY data demonstrating contacts between AH2 ¹H and netropsin ¹H resonances. The Zn²⁺/netropsin: 3′FdU complex displayed increased cytotoxicity towards PC3 prostate cancer (PCa) cells relative to the constituent components or separate complexes (e.g. Zn²⁺:3′FdU) indicating that this new structural motif may be therapeutically useful for PCa treatment.

An animated interactive 3D complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:32     

Preferential protection of the minor groove of non-operator DNA by lac repressor against methylation by dimethyl sulphate.

The binding of lactose repressor to non-operator DNA was studied by the modification of several DNA's, including glycosylated DNA, with dimethyl sulphate, which affects the minor and major grooves of DNA and single stranded DNA regions. The non-specific binding of the repressor to DNA protected the minor groove but apparently not the major groove of the DNA double helix against methylation and did not increase the content of single stranded DNA regions. This suggests that the repressor on binding to non-operator DNA makes contacts mainly in the minor groove of DNA and does not uncoil the DNA double helix. This is different from the interaction of the repressor with lactose operator DNA which occurs, as shown by Gilbert et al. (1), along both the major and the minor groove.     

Sequence-specific transitions of the torsion angle gamma change the polar-hydrophobic profile of the DNA grooves: implication for indirect protein–DNA recognition

Variations of the shape and polarity of the DNA grooves caused by changes of the DNA conformation play an important role in the DNA readout. Despite the fact that non-canonical trans and gauche- conformations of the DNA backbone angle γ (O5′–C5′–C4′–C3′) are frequently found in the DNA crystal structures, their possible role in the DNA recognition has not been studied systematically. In order to fill in this gap, we analyze the available high-resolution crystal structures of the naked and complexed DNA. The analysis shows that the non-canonical γ angle conformations are present both in the naked and bound DNA, more often in the bound vs. naked DNA, and in the nucleotides with the A-like vs. the B-like sugar pucker. The alternative angle γ torsions are more frequently observed in the purines with the A-like sugar pucker and in the pyrimidines with the B-like sugar conformation. The minor groove of the nucleotides with non-canonical γ angle conformation is more polar, while the major groove is more hydrophobic than in the nucleotides with the classical γ torsions due to variations in exposure of the polar and hydrophobic groups of the DNA backbone. The propensity of the nucleotides with different γ angle conformations to participate in the protein–nucleic acid contacts in the minor and major grooves is connected with their sugar pucker and sequence-specific. Our findings imply that the angle γ transitions contribute to the process of the protein–DNA recognition due to modification of the polar/hydrophobic profile of the DNA grooves.     

Sites of contact between lambda operators and lambda repressor.

DNA bearing lambda operator sequences was methylated by dimethyl sulfate (DMS) in the presence or absence of lambda repressor. Under the experimental conditions, DMS methylates only the purine residues. The presence of lambda repressor affects only the methylation of certain G residues in the operators. Repressor blocks the methylation of certain G's and enhances the methylation of other G's. Since the reactive ring-nitrogen of G lies in the major groove of double-stranded DNA, and the reactive ring-nitrogen of A lies in the minor groove, the above results imply that the repressor makes contacts in the major groove of the helix. The repressor effect on G-methylation is sharply confined to the three 17 base pair units within each lambda operator previously proposed as the repressor-binding sites.     

Laser Raman identification of an interaction site on DNA for arginine containing histones in chromatin.

Comparisons of the Raman spectra of DNA, chromatin, and complexes of DNA with poly-L-arginine and N-α-acetylarginine have been made. Both in native chromatin and in complexes of DNA with the arginine derivatives there is a marked decreased in the Raman intensity of the 1490±2 cm^?1 band due to guanine. Considerable evidence is presented to show that a decrease in the intensity of the 1490 cm^?1 Raman band of quanine in DNA is strong indication of a hydrogen bond being attached to the N-7 position of quanine. A specific model is presented for the interaction of the arginine residues with the guanine residues in the major groove of DNA. The Raman frequency of the histone Amide 1 band indicates that these protein molecules have a high α-helical content while the phosphate diester stretch frequency of the DNA shows the DNA to be in the B-family.     

Fluorescent d(CGCGAATTCGCG): characterization of major groove polarity and study of minor groove interactions through a major groove semantophore conjugate.

The major and minor groove in duplex DNA are sites of specific molecular recognition by DNA-binding agents such as proteins, drugs and metal complexes and have functional significance. In view of this, understanding of the inherent differences in their environment and the allosteric information transfer between them induced by DNA-binding agents assumes importance. Site-specific incorporation of 5-aminodansyl-dU, (U*) in oligonucleotides d(CGCGAAU*TCGCG) and d(CGCGAATU*CGCG) leads to fluorogenic nucleic acids, in which the reporter group resides in the major groove. The fluorescent observables from such a probe are used to estimate the dielectric constant of the major groove to be approximately 55D, in comparison to the reported non polar environment of the minor groove (approximately 20D) in poly d[AT]-poly d[AT]. An exclusive minor groove event such as DNA-netropsin association can be quantitatively monitored by fluorescence of the dansyl moiety located in the major groove. This suggests existence of an information network among the two grooves. The fluorescent DNA probes as reported here may have potential applications in the study of structural polymorphisms in DNA, DNA-ligand interactions and triple helix structure.