Effect of Cibacron blue F3GA on oligonucleotide binding site of estradiol--receptor complexes of mouse uterine cytosol

Strong ionic interactions in noncovalent complexes between poly(ethylene imine), a cationic electrolyte, and Cibacron Blue, a nucleotide mimic--implications for oligonucleotide vectors

Cationic polymers can bind DNA to form polyplexes, which are noncovalent complexes used for gene delivery into the targeted cells. For more insight on such biologically relevant systems, the noncovalent complexes between the cationic polymer poly(ethylene imine) (PEI) and the nucleotide mimicking dye Cibacron Blue F3G-A (CB) were investigated using mass spectrometry methods. Two PEIs of low molecular weight were utilized (Mn  ≈ 423 and 600 Da). The different types of CB anions produced by Na(+)/H(+) exchanges on the three sulfonic acid groups of CB and their dehydrated counterparts were responsible for complex formation with PEI. The CB anions underwent noncovalent complex formation with protonated, but not with sodiated PEI. A higher proportion of cyclic oligomers were detected in PEI423 than PEI600, but both architectures formed association products with CB. Tandem mass spectrometry studies revealed a significantly stronger noncovalent interaction between PEI and dehydrated CB than between PEI and intact CB.

Molecular structures of edge-sharing square-planar dinuclear complexes with unsaturated bridges

The dinuclear complexes of transition metal ions of type [M(2)(mu,eta(1)-XY)(2)L(4)], where XY is an unsaturated ligand that can act as a four-electron or a two-electron donor through the X atom, appear in two molecular conformations depending on whether the coordination planes around the two metal atoms are coplanar or bent. In both structures the geometry of the X atom is planar, corresponding to an sp(2) hybridization. An ab initio theoretical study on 43 representative complexes, complemented with a structural database analysis, provides a rationale for the experimentally observed structures.

Analysis of negatively charged dye-binding antibodies reactive with double-stranded DNA and heparan sulfate in serum from patients with rheumatic diseases

Antibodies to double-stranded (ds) DNA are characteristically present in serum from patients with systemic lupus erythematosus (SLE). Recently, anti-dsDNA antibodies have been shown to have the capacity to react with a diversity of molecules with repeating negative charges. Using the anionic dye Cibacron blue F3GA, bound to crosslinked agarose, we analysed the nature of antibodies capable of reacting with this dye in serum samples from patients with various rheumatic diseases. The dye-antibody complex could easily be split by eluting with solutions of increasing ionic strength, suggesting that the interaction is ionic in nature. Pepsin-digested F(ab')2 antibodies retained the capacity to bind Cibacron blue, confirming that the binding occurred via antigen-binding sites on the antibody molecule. The eluates obtained from dye-ligand chromatography of active SLE sera contained antibodies to both dsDNA and heparan sulfate, while those of sera from patients with other non-SLE rheumatic diseases contained antibodies only against heparan sulfate. Furthermore, the dye-ligand eluates of sera from patients with active SLE and other non-SLE rheumatic diseases were found to contain increased amounts of IgG. In one patient with SLE, levels of antibodies to dsDNA and heparan sulfate, and the amounts of total IgG in dye-ligand eluates, were shown to be correlated with disease activity.

Oligodeoxynucleotide base recognition by steroid hormone receptors

Oligodeoxynucleotides covalently linked to cellulose were used as probes of the DNA-binding domains of mouse steroid holoreceptors. With uterine cytosol estrogen receptor (E2R) the relative binding order, in prior studies, was oligo(dG) greater than oligo(dT) greater than or equal to oligo(dC) much greater than oligo(dA) greater than oligo(dI). The binding reactions were salt-sensitive with an optimal KCl concentration of 0.1-0.2 M. There was no enhancement of binding by activation, either temperature- or salt-induced. In the present study, using the oligomer ligands at a lower concentration, oligo(dT) binding was greater than that to oligo(dC). Quantitative differences in oligodeoxynucleotide binding were elicited by a number of inhibitors. These differences are again seen by exposure of E2R to chaotropic salts such as SCN-, ClO-4 and NO3- as well as to putative modifiers of receptor amino acids, ie, iodoacetamide, 1,2 cyclohexanedione, and Rose Bengal. These results, and the quantitative differences following heat and purification, led to a designation of two types of subsites within the DNA-binding domain of uterine E2R. These are stable G sites, which interact with oligo(dG); and labile N sites, which bind to oligo(dT), oligo(dC) and oligo(dA). Stimulation of binding to N sites and stabilization of the holoreceptor was effected by histones H2A and H2B. However, the differential response to incubation at 37 degrees C was not altered by addition of H2B. Treatment of uterine E2R by limited proteolysis also eliminated the stimulatory response to H2B. The above data, as well as prior studies, indicate that steroid holoreceptors can discriminate between the structural features of deoxynucleotide bases and this recognition process can be modulated by accessory proteins.

The polynucleotide binding sites of estradiol receptor complexes

As a model for interaction of steroid receptors with DNA, the binding of estradiol receptor complexes (E2R) to oligodeoxynucleotides, covalently linked to cellulose, was studied in detail. Binding was optimal at concentrations of monovalent cationic salts at, or near, isotonic levels and was selective for intracellular receptors in contrast to extracellular steroid binding proteins. Among the oligomers, the order of affinity was oligo dG greater than oligo dT greater than oligo dC greater than oligo dA greater than oligo dI. The binding to oligo dG was stable to 37 degrees C exposure and the processes of adsorption and desorption, while reactivity with oligo dT, oligo dC and oligo dA was labile. The decrease in binding following purification was restored by histone 2B. Oligo dG binding was the most resistant to inhibition by cibacron blue F3GA (CB) and pyridoxal-5-phosphate. On the basis of these data, a hypothesis is proposed for the interaction of mouse uterine cytosol E2R with prevalent nonspecific and putative specific sequences of DNA.

Interaction of myosin subfragment 1 with Cibacron Blue F3GA

Cibacron Blue F3GA and its immobilized derivatives have been shown before to bind and inhibit nucleotide-dependent enzymes and, among them, myosin subfragment 1. Experiments have been carried out to examine the mechanism of the subfragment 1--dye interaction. Binding of subfragment 1 to immobilized dye (Affi-Gel Blue) does not involve the ATP binding site on myosin. Subfragment 1 hydrolyzes MgATP and CaATP while bound to the Affi-Gel Blue column. Inactivated subfragment 1, which contains [3H]ADP noncovalently trapped at the active site, binds and elutes from the Affi-Gel Blue column in the same manner as unmodified, active protein. Free Cibacron Blue inhibits the ATPase activity of subfragment 1. The inhibition is pH, salt, and time dependent. Complete inhibition correlates with the noncovalent binding of four to five dye molecules per mole of subfragment 1. Three to four of these dye molecules can be preferentially removed from subfragment 1 in the presence of 1 M KCl without relieving the inhibition. This inhibition, which can be traced to one dye molecule per subfragment 1, is reversible and is facilitated in the presence of MgADP and MgATP, suggesting that the dye does not bind at the active site of subfragment 1. Our observations are explained in terms of hydrophobic and electrostatic protein--dye interactions.

Binding of Cibacron blue F3GA to the flavin and NADH sites in cytochrome b5 reductase

The behaviour of cytochrome b5 reductase holoenzyme and apoenzyme toward blue-dextran--Sepharose has been studied. Holoenzyme was adsorbed at low ionic strength and could be eluted with 100 microM NADH or NAD+. Flavin-free enzyme was even more strongly bound and could be eluted with 1 M NaCl, or 100 microM NADH + 10 microM FAD. Separately the cofactors were without effect. FMN was less effective than FAD. ADP and AMP eluted nothing. Cibacron blue F3GA was found to exert a mixed inhibition on NADH oxidation. Dye binding to holoenzyme elicited a characteristic red shift in its spectrum. Comparison of the difference spectrum amplitude at 680 and 585 nm showed the presence of a second binding mode at higher dye concentrations. These results point to the existence for cytochrome b5 reductase of two binding sites with high affinity for blue-dextran--Sepharose: the NADH binding site and flavin binding site. For the latter it is clear that isoalloxazine pocket must play a role in dye binding. Cytochrome b5 reductase is the second flavoenzyme which has been shown to have affinity for immobilized dye at the flavin site, the first one being flavocytochrome b2, and FMN-dependent enzyme [D. Pompon and F. Lederer (1978) Eur. J. Biochem. 90, 563--569].

Specificity of oligodeoxynucleotide binding of mouse uterine cytosol estradiol receptors

The relative capacities of oligodeoxynucleotides, covalently linked to cellulose, to bind estradiol receptor complexes (E2R) of mouse uterine cytosol have been shown to follow the order oligo(dG) > oligo(dT) greater than or equal to oligo(dC) > oligo(dA). The E2R . oligo(dT)-cellulose-binding reaction is more sensitive to Cibacron blue F3GA than is E2R . oligo(dG)-cellulose or oligo(dC)-cellulose binding. Preformed E2R . oligo(dT)- or oligo(dC)-cellulose complexes are dissociated more readily by lower concentrations of KCl or Cibacron blue F3GA than is the E2R . oligo(dG)-cellulose complex. Preincubation of E2R at 37 degrees C results in a rapid loss of binding ability towards oligo(dT)- and oligo(dC)-cellulose, while up to 90% of the binding ability to oligo(dG)-cellulose is retained. On the basis of the differential sensitivities of E2R to temperature and the inhibition by Cibacron blue F3GA of the binding reaction, it is suggested that the polynucleotide-binding domain consists of two types of subsites, one of which has a higher affinity for oligo(dG) residues and the other of which recognizes oligo(dT), oligo(dC), and, to a lesser extent, oligo(dA).

Purification of chicken intestinal receptor for 1,25-dihydroxyvitamin D

The 3.3S chicken intestinal receptor for 1,25-dihydroxyvitamin D [1,25-(OH)2D] has been purified approximately 86,000-fold from the cytosolic fraction. The receptor was selectively precipitated with Polymin P from high-speed supernatants derived from 800 g of intestinal mucosa and then sequentially chromatographed on DNA-cellulose. Sephacryl, blue dextran-Sepharose, DNA-cellulose, and heparin-Sepharose. Polyacrylamide gel electrophoresis of 8-10 microgram of the purified receptor in sodium dodecyl sulfate indicated the presence of one major and three minor protein bands of molecular weights 50,000-65,000. Sucrose gradient analysis of the purified material in 0.3 M KCl suggested that a fraction of the receptor remained complexed to the 1,25-(OH)2D and that its sedimentation property of 3.3S remained unchanged. These results represent a major purification of the chick intestinal receptor for 1,25-(OH)2D, an extremely rare and labile protein whose isolation is estimated to require a 200,000-fold purification. Of primary importance is the observation tht affinity ligands such as DNA and blue dextran can effect major purification of this protein, lending credence to the hypothesis that the 1,25-(OH)2D receptor functions within the cell nucleus by altering the expression of specific genes.

Stimulation of oligonucleotide binding of estradiol receptor complexes by accessory proteins

During purification of E2R using oligo(dT)-cellulose chromatography, a receptor accessory factor (RAF) was identified in the cytosol of mouse kidney. This factor stimulates the binding of purified E2R to oligo(dT)-, oligo(dC)-, and oligo(dA)-cellulose as well as to DNA cellulose. It is a heat-stable, trypsin-resistant protein with an apparent molecular weight of between 10 and 30,000 daltons. Although structurally unrelated, similar stimulation of oligonucleotide binding was seen with calf thymus histones and, to a lesser extent, egg white lysozyme. Individual histones, especially H2a, H2B, and H3, also facilitate rebinding of purified E2R to oligo(dT)-cellulose, while H1 is less effective. Furthermore, histones stabilize the holoreceptor during sedimentation at 4 degrees and 12 degrees C. The N- and C-terminal half molecules of H2b were generated by cyanogen bromide-mediated cleavage and the N-terminal half was found to duplicate the effects of the parent molecule, both in binding and holoreceptor stabilization. These data suggest that the in vivo binding of E2R to DNA can be modulated by accessory proteins of cytosol and nuclear origin.