Binding Of Spermidine Research Articles

Modulation of GluA2-γ5 synaptic complex desensitization, polyamine block and antiepileptic perampanel inhibition by auxiliary subunit cornichon-2.

Synaptic complexes of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPARs) with auxiliary subunits mediate most excitatory neurotransmission and can be targeted to treat neuropsychiatric and neurological disorders, including epilepsy. Here we present cryogenic-electron microscopy structures of rat GluA2 AMPAR complexes with inhibitory mouse γ5 and potentiating human cornichon-2 (CNIH2) auxiliary subunits. CNIH2 appears to destabilize the desensitized state of the complex by reducing the separation of the upper lobes in ligand-binding domain dimers. At the same time, CNIH2 stabilizes binding of polyamine spermidine to the selectivity filter of the closed ion channel. Nevertheless, CNIH2, and to a lesser extent γ5, attenuate polyamine block of the open channel and reduce the potency of the antiepileptic drug perampanel that inhibits the synaptic complex allosterically by binding to sites in the ion channel extracellular collar. These findings illustrate the fine-tuning of synaptic complex structure and function in an auxiliary subunit-dependent manner, which is critical for the study of brain region-specific neurotransmission and design of therapeutics for disease treatment.

Spermidine Binding to the Acetinobacter baumannii Efflux Protein AceI Observed by Near-UV Synchrotron Radiation Circular Dichroism Spectroscopy

The aim of this work was to test polyamines as potential natural substrates of the Acinetobacter baumannii chlorhexidine efflux protein AceI using near-UV synchrotron radiation circular dichroism (SRCD) spectroscopy. The Gram-negative bacterium A. Baumannii is a leading cause of hospital-acquired infections and an important foodborne pathogen. A. Baumannii strains are becoming increasingly resistant to antimicrobial agents, including the synthetic antiseptic chlorhexidine. AceI (144-residues) was the founding member of the recently recognised PACE family of bacterial multidrug efflux proteins. Using the plasmid construct pTTQ18-aceI(His6) containing the A. baumannii aceI gene directly upstream from a His6-tag coding sequence, expression of AceI(His6) was amplified in E. coli BL21(DE3) cells. Near-UV (250–340 nm) SRCD measurements were performed on detergent-solubilised and purified AceI(His6) at 20 °C. Sample and SRCD experimental conditions were identified that detected binding of the triamine spermidine to AceI(His6). In a titration with spermidine (0–10 mM), this binding was saturable and fitting of the curve for the change in signal intensity produced an apparent binding affinity (KD) of 3.97 ± 0.45 mM. These SRCD results were the first experimental evidence obtained for polyamines as natural substrates of PACE proteins.

Quantitative input-output dynamics of a c-di-GMP signal transduction cascade in Vibrio cholerae.

Bacterial biofilms are multicellular communities that collectively overcome environmental threats and clinical treatments. To regulate the biofilm lifecycle, bacteria commonly transduce sensory information via the second messenger molecule cyclic diguanylate (c-di-GMP). Using experimental and modeling approaches, we quantitatively capture c-di-GMP signal transmission via the bifunctional polyamine receptor NspS-MbaA, from ligand binding to output, in the pathogen Vibrio cholerae. Upon binding of norspermidine or spermidine, NspS-MbaA synthesizes or degrades c-di-GMP, respectively, which, in turn, drives alterations specifically to biofilm gene expression. A long-standing question is how output specificity is achieved via c-di-GMP, a diffusible molecule that regulates dozens of effectors. We show that NspS-MbaA signals locally to specific effectors, sensitizing V. cholerae to polyamines. However, local signaling is not required for specificity, as changes to global cytoplasmic c-di-GMP levels can selectively regulate biofilm genes. This work establishes the input-output dynamics underlying c-di-GMP signaling, which could be useful for developing bacterial manipulation strategies.

Molecular aspects of the interaction of spermidine and α-chymotrypsin

Polyamines such as spermidine are essential for survival. The purpose of the present study was to investigate how spermidine could influence the conformation, thermal stability and the activity of α-chymotrypsin. The influence of spermidine on the structure and stability of α-Chymotrypsin (α-Chy) explored using different spectroscopy method and molecular docking simulations. The stability and activity of α-Chy were increased in the presence of spermidine. Increasing of the α-Chy absorption in the presence of spermidine was as a result of the formation of a spermidine ⿿ α-Chy complex. The results of fluorescence spectroscopic measurements suggested that spermidine has a vigorous ability to quench the intrinsic fluorescence of α-Chy through the dynamic quenching procedure. Near and Far-UV CD studies also confirmed the transfer of aromatic residues to a more flexible environment. The absorption increasing of α-Chy in the presence of spermidine was as a result of the formation of spermidine ⿿ α-Chy complex. Molecular docking results also revealed the presence of one binding site with a negative value for the Gibbs free energy of the binding of spermidine to α-Chy. Further, the docking study revealed that van der Waals interactions and hydrogen bonds play a main role in stabilizing the complex.

Polyamine biosynthesis and transport mechanisms are crucial for fitness and pathogenesis of Streptococcus pneumoniae

Polyamines such as cadaverine, putrescine and spermidine are polycationic molecules that have pleiotropic effects on cells via their interaction with nucleic acids. Streptococcus pneumoniae (the pneumococcus) is a Gram-positive pathogen capable of causing pneumonia, septicaemia, otitis media and meningitis. Pneumococci have a polyamine transport operon (potABCD) responsible for the binding and transport of putrescine and spermidine, and can synthesize cadaverine and spermidine using their lysine decarboxylase (cad) and spermidine synthase (speE) enzymes. Previous studies from our laboratory have shown that an increase in PotD expression is seen following exposure to various stresses, while during infection, potD inactivation significantly attenuates pneumococcal virulence, and anti-PotD immune responses are protective in mice. In spite of their relative importance, not much is known about the global contribution of polyamine biosynthesis and transport pathways to pneumococcal disease. Mutants deficient in polyamine biosynthesis (ΔspeE or Δcad) or transport genes (ΔpotABCD) were constructed and were found to be attenuated in murine models of pneumococcal colonization and pneumonia, either alone or in competition with the wild-type strain. The ΔspeE mutant was also attenuated during invasive disease, while the potABCD and cad genes seemed to be dispensable. HPLC analyses showed reduced intracellular polyamine levels in all mutant strains compared with wild-type bacteria. High-throughput proteomic analyses indicated reduced expression of growth, replication and virulence factors in mutant strains. Thus, polyamine biosynthesis and transport mechanisms are intricately linked to the fitness, survival and pathogenesis of the pneumococcus in host microenvironments, and may represent important targets for prophylactic and therapeutic interventions.

Elucidation of spermidine interaction with nucleotide ATP by multiple NMR techniques

Interaction of polyamines with nucleotides plays a key role in many biological processes. Here we use multiple NMR techniques to characterize interaction of spermidine with adenosine 5'-triphosphate (ATP). Two-dimensional (1)H-(15)N spectra obtained from gs-HMBC experiments at varied pH show significant shift of N-1 peak around pH 2.0-7.0 range, suggesting that spermidine binds to N-1 site of ATP base. The binding facilitates N-1 deprotonation, shifting its pK(a) from 4.3 to 3.4. By correlating (15)N and (31)P chemical shift data, it is clear that spermidine is capable of concurrently binding to ATP base and phosphate sites around pH 4.0-7.0. The self-diffusion constants derived from (1)H PFG-diffusion measurements provide evidence that binding of spermidine to ATP is in 1:1 ratio, and pH variations do not induce significant nucleotide self-association in our samples. (31)P spectral analysis suggests that at neutral pH, Mg(2+) ion competes with spermidine and shows stronger binding to ATP phosphates. From (31)P kinetic measurements of myosin-catalyzed ATP hydrolysis, it is found that binding of spermidine affects the stability and reactivity of ATP. These NMR results are important for advancing the studies on nucleotide-polyamine interaction and its impact on nucleotide structures and activities under varied conditions.

Incomplete Ion Dissociation Underlies the Weakened Attraction between DNA Helices at High Spermidine Concentrations

We have investigated the salt sensitivity of the hexagonal-to-cholesteric phase transition of spermidine-condensed DNA. This transition precedes the resolubilization of precipitated DNA that occurs at high spermidine concentration. The sensitivity of the critical spermidine concentration at the transition point to the anion species and the NaCl concentration indicates that ion pairing of this trivalent ion underlies this unusual transition. Osmotic pressure measurements of spermidine salt solutions are consistent with this interpretation. Spermidine salts are not fully dissociated at higher concentrations. The competition for DNA binding among the fully charged trivalent ion and the lesser charged complex species at higher concentrations significantly weakens attraction between DNA helices in the condensed state. This is contrary to the suggestion that the binding of spermidine at higher concentrations causes DNA overcharging and consequent electrostatic repulsion.

Human deoxyhypusine synthase: interrelationship between binding of NAD and substrates

Deoxyhypusine synthase catalyses the NAD-dependent transfer of the butylamine moiety from the polyamine, spermidine, to a specific lysine residue of a single cellular protein, eukaryotic translation-initiation factor 5A (eIF5A) precursor. The native enzyme exists as a tetramer of four identical subunits and contains four binding sites for NAD. The binding of spermidine and NAD was studied by a filtration assay. [(3)H]Spermidine binding to the enzyme was not detectable alone or in the presence of the eIF5A precursor, but was detected only in the presence of NAD or NADH, suggesting that a NAD/NADH-induced conformational change is required for the binding of spermidine. A strong NAD-dependent binding was also observed with a spermidine analogue, N(1)-guanyl-1, 7-diamino[(3)H]heptane (GC(7)), but not with [(14)C]putrescine or [(14)C]spermine. Although [(3)H]NAD binding to the enzyme occurred in the absence of spermidine, its affinity for the enzyme was markedly enhanced by spermidine, GC(7) and also by the eIF5A precursor. The maximum binding for NAD and spermidine was estimated to be approximately 4 molecules each/enzyme tetramer. The dependence of spermidine binding on NAD and the modulation of binding of NAD by spermidine and the eIF5A precursor suggest intricate relationships between the binding of cofactor and the substrates, and provide new insights into the reaction mechanism.

Binding of Spermidine and Putrescine to Energized Liver Mitochondria

The binding of spermidine and putrescine to mitochondrial membranes was studied by applying a thermodynamic model of ligand–receptor interactions developed both for equilibrium and far-from-equilibrium binding processes (V. Di Noto, L. Dalla Via, A. Toninello, and M. VidaliMacromol. Theory Simul.5, 165–181, 1996). Results demonstrate the presence of two monocoordinated binding sites (S1and S2) for spermidine and one monocoordinated binding site (S2) for putrescine, all exhibiting high capacity and low affinity. It is proposed that differences in the polyamines' flexibility and hydrophilicity perhaps contributes to the observed variations in their interactions with the two sites. A comparison of the binding parameters of these polyamines with those of spermine reveals differences in the specific function of the S1and S2sites, identified in studies of spermine binding (L. Dalla Via, V. Di Noto, D. Siliprandi, and A. ToninelloBiochim. Biophys. Acta1284, 247–252, 1996).

Spermidine-preferential Uptake System in Escherichia coli: IDENTIFICATION OF AMINO ACIDS INVOLVED IN POLYAMINE BINDING IN PotD PROTEIN

Spermidine-binding sites on PotD protein, substrate-binding protein in periplasm, in the spermidine-preferential uptake system in Escherichia coli were studied by measuring polyamine transport activities of right-side-out membrane vesicles with mutated PotD proteins prepared by site-directed mutagenesis of the potD gene and by measuring polyamine binding activities of these mutated PotD proteins. Polyamine transport activities of the mutated PotD proteins paralleled their polyamine binding activities. It was found that Trp-34, Thr-35, Glu-36, Tyr-37, Ser-83, Tyr-85, Asp-168, Glu-171, Trp-229, Trp-255, Asp-257, Tyr-293, and Gln-327 of PotD protein were involved in the binding to spermidine. When spermidine uptake activities were measured in intact cells expressing the mutated PotD proteins, it was found that Glu-171, Trp-255, and Asp-257 were more strongly involved in the binding of spermidine to PotD protein than the other amino acids listed above. The dissociation constants of spermidine for the mutated PotD proteins at Glu-171, Trp-255, and Asp-257 increased greatly in comparison with those for the other mutated PotD proteins. Since these three amino acids clearly interact with the diaminopropane moiety of spermidine, the results are in accordance with the finding that PotD protein has a higher affinity for spermidine than for putrescine. Putrescine was found to bind at the position of the diaminobutane moiety of spermidine.

The binding of polyamines and magnesium to DNA

1. The binding of spermine and Mg 2+ to DNA has been investigated using the dye arsenazo III to measure unbound cations. 2. The apparent dissociation constant, K d, of DNA for spermine has been found to be 7.4 ± 3.9 × 10 −8 M and that for Mg 2+, 6.5 ± 3.3 × l0 −7 M. 3. Binding of spermine in the presence of 1 mM Mg 2+ has been shown to have a K d of about 4 × 10 −6 M. 4. Magnesium ion (2 mM) halves the concentration of spermine needed to cause DNA aggregation. 5. Spermidine binds to DNA with a similar affinity to spermine but 3,3′-iminobispropylamine and 1,5,9,13-tetra-azatridecane bind with a lower affinity. The naturally occurring polyamines thus have a higher affinity for DNA than the related polyamines which do not occur naturally. 6. Binding of spermine or spermidine to DNA alters the spectrophotometric absorbance of DNA at 260 nm.

Effects of spermidine and hexaamminecobalt(III) on thymine imino proton exchange

We examine the influence of spermidine and hexaamminecobalt(III) binding on DNA base pair dynamics. Proton NMR line-width measurements are used to monitor the exchange of the thymine imino proton in poly[dA].poly[dT] and in the alternating copolymer [d(AT)]15.[d(AT)]15. We employ the treatment by Benight et al. (1988) of diffusion effects in imino proton exchange to estimate catalytic rate constants and to extract apparent equilibrium constants for the interconversion between closed (nonexchanging) and solvent-accessible (exchangeable) states of the base pairs. The salt dependence of the spermidine-catalyzed imino proton exchange in poly[dA].poly[dT] is qualitatively described by this theory. van't Hoff analysis of the temperature dependence of the apparent equilibrium constants suggests that the binding of spermidine and hexaamminecobalt(III) lowers the energy difference between the nonexchanging and exchanging states of the AT base pair in both duplexes.

Binding of spermidine to a unique protein in thin-layer tobacco tissue culture.

The mechanism by which spermidine induces the appearances of floral buds in thin-layer tobacco (Nicotiana tabacum) tissue culture was studied by following the fate of the radioactive compound. [3H]Spermidine was taken up rapidly by the tissue, and after a brief lag, a portion was bound to trichloroacetic acid precipitable macromolecules. Such binding increased to a maximum on day 4 of culture, coinciding with the onset of bud differentiation, and declined thereafter until shortly before flowering. About 82% of the label in the trichloroacetic acid precipitate remained as spermidine, 14% was metabolized to putrescine, 3% to spermine, and 1% to gamma-aminobutyric acid. Spermidine was covalently bound to a protein with a molecular size of about 18 kilodaltons. Hydrolysis of this protein and analysis of the labeled entities revealed 81% spermidine, 16% putrescine, and 3% spermine. This post-translational modification of a unique protein by attachment of spermidine may be causally connected to the appearance of flower buds in thin-layer tobacco cultures.

1H NMR study of the base-pairing reactions of d(GGAATTCC): salt and polyamine effects on the imino proton exchange.

Salts and polyamines have a variety of effects on the physical properties of DNA, including stabilization against thermal melting. We wished to gain greater insight into the mechanism of this stabilization by ascertaining its effect on the dynamics of base opening and closing reactions, as measured by NMR. Since the binding of spermidine(3+) is influenced by salt, and since spermidine may act as a base catalyst in proton exchange reactions, we have undertaken a study of salt and base catalyst effects on the imino proton exchange kinetics of a model oligomeric DNA. The selective longitudinal NMR relaxation rates of the hydrogen-bonded imino protons of the self-complementary octadeoxyribonucleotide d(GGAATTCC) monitor the rate of the base-catalyzed chemical exchange of these protons with solvent water. The exchange rates thus obtained provide a sensitive measure of the base-pair opening reactions of the DNA duplex. Under conditions of low pH and no added base catalyst, the NMR relaxation rates allow the determination of kd, the rate constant for the dissociation of the octameric duplex into single strands. Titration with the base catalyst tris(hydroxymethyl)aminomethane allows the determination of kop, the rate constant for the localized opening of individual base pairs, prior to dissociation. A significant Na+ concentration dependence is found for kd. From an analysis of this dependence, it is determined that 0.6 +/- 0.1 sodium ion is released during the dissociation event. The activation energy for helix dissociation (200 +/- 5 kJ/mol) is not dependent on the sodium ion concentration, indicating that the dissociation is entropically driven by the release of bound sodium ions.(ABSTRACT TRUNCATED AT 250 WORDS)

Spermidine in mammalian lymphocytes and sea urchin embryos: uptake and labeling of macromolecules.

We have studied the uptake and attachment of spermidine and some of its metabolites to cellular macromolecules in a variety of cell systems. We have selected systems which demonstrate significant uptake of polyamines when the polyamine is presented in the external environment of the cell. We chose to work with cells which are capable of increasing their metabolic activity in a manner approaching synchrony in response to a biological stimulus. In the presence of exogenous radioactive spermidine and a stimulus provoking focused cell function the cell takes up the spermidine and actively utilizes it in a biosynthetic manner. We have traced the metabolic fate of the radioactive spermidine under these conditions. The cells which we have primarily studied are young sea urchin embryos and mammalian lymphocytes. The mammalian lymphocytes we have studied include murine splenic lymphocytes, normal human peripheral lymphocytes and peripheral lymphocytes from patients with chronic lymphocytic leukemia (CLL). These represent a continuation of earlier studies where we showed that these cells can be activated by a B-cell mitogen and this activation can be abrogated by simultaneous exposure to the diacetyl derivative of putrescine or of its analogue 1, 6 diaminohexane (1–3). The sea urchin embryo studies are a continuation of earlier investigations where we documented the covalent binding of spermidine to a unique protein in very young sea urchin embryos (4). Both mitogen activation and the event of fertilization can be thought of as agents inducing “natural” synchrony and consequent increased uptake and utilization of exogenous polyamines. Certain parallels between the two biological systems as we observe them will be described. No attempt is made in this report to be inclusive in describing studies from other laboratories of polyamines associated with macromolecules. Thus, this is in the form of a progress report of our current experiments.KeywordsChronic Lymphocytic LeukemiaMurine SpleenExogenous PolyamineDiacetyl DerivativeFriend Erythroleukemia CellThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

A chromatin core particle obtained by selective cleavage of histones by clostripain.

Rat liver chromatin core particles digested with clostripain yield a structurally well-defined nucleoprotein particle with an octameric core made up of fragmented histone species (designated H'2A, H'2B, H'3 and H'4, respectively) after selective loss of a sequence segment located in the N-terminal region of each core histone. Sequential Edman degradation and carboxypeptidase digestion unambiguously establish that histones H2A, H2B, H3 and H4 are selectively cleaved at the carboxyl side of Arg 11, Lys 20, Arg 26 and Arg 19 respectively and that the C-terminal sequences remain unaffected. Despite the loss of the highly basic N-terminal regions, including approximately 17% of the total amino acids, the characteristic structural organization of the nucleosome core particle appears to be fully retained in the proteolyzed core particle, as judged by physicochemical and biochemical evidence. Binding of spermidine to native and proteolyzed core particles shows that DNA accessibility differs markedly in both structures. As expected the proteolyzed particle, which has lost all the in vivo acetylation sites, is not enzymatically acetylated, in contrast to the native particle. However, proteolyzed histones act as substrates of the acetyltransferase in the absence of DNA, as a consequence of the occurrence of potential acetylation sites in the core histones thus rendered accessible. The possible role of the histone N-terminal regions on chromatin structure and function is discussed in the light of the present observations with the new core particle obtained by clostripain proteolysis.

Transglutaminase-mediated modifications of the rat sperm surface in vitro.

Two transglutaminase-mediated modifications of the rat epididymal spermatozoon surface were demonstrated in vitro. Transglutaminase was effective in promoting the binding of spermidine to the sperm. Moreover, the enzyme, by reacting with one of the major proteins secreted by the rat seminal vesicle epithelium, produced a modified form of the protein with a higher molecular weight and the capability of binding to the sperm cells. A specific physiological role for the enzyme, bringing about modifications of the rat sperm surface in the seminal fluid environment, is suggested.

Binding of spermidine to transfer ribonucleic acid.

The binding of spermidine to yeast tRNAPhe and Escherichia coli tRNAGlu2 at low and high ionic strength was studied by equilibrium dialysis. Once corrected for the expected Donnan effect, the binding at low ionic strength obeys the simple relationship of equivalent binding sites, and cooperative binding of spermidine to tRNA could not be detected. At low ionic strength (0.013 M Na+ ion), tRNAPhe (yeast) has 13.9 +/- 2.3 strong spermidine binding sites per molecule with Kd = 1.39 X 10(-6) M and a few weak spermidine binding sites which were inaccessible to experimentation; tRNAGlu2 (E. coli) has 14.8 +/- 1.6 strong spermidine binding sites and 4.0 +/- 0.1 weak spermidine binding sites with Kd = 1.4 X 10(-6) M and Kd = 1.23 X 10(-4) M, respectively. At high ionic strength (0.12 M monovalent cation) and 0.01 M Mg2+, tRNAPhe (yeast) has approximately 13 strong spermidine binding sites with an apparent Kd = 3.4 X 10(-3) M while the dimeric complex tRNAPhe X tRNAGlu2 has 10.4 +/- 1.2 strong spermidine binding sites per monomer with an apparent Kd = 2.0 X 10(-3) M. In the presence of increasing Na+ ion or K+ ion concentration, spermidine binding data do not fit a model for competitive binding to tRNA by monovalent cations. Rather, analysis of binding data by the Debye-Hückel approximation results in a good fit of experimental data, indicating that monovalent cations form a counterion atmosphere about tRNA, thus decreasing electrostatic interactions. On the basis of equilibrium binding analyses, it is proposed that the binding of spermidine to tRNA occurs predominantly by electrostatic forces.

Role of spermidine in the activity of sn-glycerol-3-phosphate acyltransferase from Escherichia coli

The integral membrane protein, sn-glycerol-3-phosphate acyltransferase, catalyzes the first committed step in phospholipid synthesis, and both acyl-CoA and acyl-acyl carrier protein can be used as acyl donors in this reaction. We found that spermidine increased the specific activity of the acyltransferase when either substrate was used as the acyl donor. Magnesium, as well as other cations, also increased acyltransferase activity but were not nearly as effective as spermidine. Two roles for spermidine in this reaction were deduced from our data. First, spermidine dramatically lowered the K m for glycerol 3-phosphate resulting in an overall rate enhancement when either substrate was used as the acyl donor. This effect was attributed to the modification of the acyl-transferase environment due to the binding of spermidine to membrane phospholipids. A second effect of spermidine was evident only when acyl-acyl carrier protein was used as substrate. Using this acyl donor, a pH optimum of 7.5 was found in the absence of spermidine, but in its presence, the pH optimum was shifted to 8.5. Between pH 7.5 and 8.5, palmitoyl-acyl carrier protein undergoes a conformational change to a more expanded, denatured state and its activity in the acyltransferase assay decreases dramatically. Spermidine restored the native conformation of palmitoyl-acyl carrier protein at pH 8.5, thus accounting for the majority of rate enhancement observed at elevated pH.

Equilibrium dialysis studies of polyamine binding to DNA.

AbstractBinding constants and binding site sizes for the interactions of the polyamines spermine (+4), spermidine (+3), and putrecine (+2) with helical DNA have been determined as a function of ionic conditions and temperature by equilibrium dialysis using 14C‐labeled polyamines. In addition, competition equilibrium dialysis has been used to determine binding parameters for the divalent cations putrescine and Mg2+ from the competitive effect of these ions on the binding of spermine or spermidine. In all cases, the logarithm of the binding constant (log Kobs) varies linearly with the logarithm of the monovalent salt concentration; the slopes d log Kobs/d log[NaCl] are proportional to the valence of the ligand, and values of the extrapolated binding constants at 1M NaCl obtained from the intercepts are small (of order 1–10M−1). In those cases examined, Kobs is insensitive to temperature; the free energy of binding is predominantly entropic. Consequently, polymines as DNA‐binding ligands behave analogously to the oligolysìnes investigated previously [cf. Record, Lohman & de Haseth (1976) J. Mol. Biol. 107, 145–158; Lohman, de Haseth & Record (1980) Biochemistry 19, 3522–3530]. The interactions of these oligocations with DNA are predominantly electrostatic and are driven by the release of thermodynamically bound electrolyte ions from the vicinity of the DNA. The extent to which these oligocations are localized at individual phosphate binding sites or delocalized on the DNA molecule is currently not known.