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At least 1,009 records · Page 56Linked to original sources
PubMed1999

Copper(II) complexes of a nonsteroidal anti-inflammatory drug niflumic acid. Synthesis, crystal structure of tetrakis-mu-(2-[3-(trifluoromethyl) phenyl]aminonicotinato)bis(dimethylsulfoxide)-dicopper(II) complex at 190 K. Anti-inflammatory properties.

The synthesis and characterization of three complexes with a potent nonsteroidal anti-inflammatory drug niflumic acid {2-[3-(trifluoromethyl)phenyl]aminonicotinic acid} with formula [Cu(niflumato)2L] (L = H2O, DMSO = dimethylsulfoxide, DMF = N,N-dimethylformamide) were investigated. The crystal and molecular structure of the {Cu(niflumato)2(DMSO)}2 was reported. Crystallographic data are as follows: monoclinic system, space group P2(1)/n, Z = 2, a = 11.1318(8), b = 17.513(2), c = 15.336(1) A, beta = 103.316(8) degrees, V = 2909.4(4) A3. The structure was refined to R = 0.030 and wR = 0.037 for 3702 reflections with I > sigma (I). It consists of centrosymmetric binuclear units with the Cu-Cui (symmetry code i: 1-x, -y, 1-z) distance between two centrosymmetrically related ions of 2.6272(5) A. Each Cu(II) ion in [Cu2(DMSO)2(mu-niflumato)4] is coordinated to an apical dimethylsulfoxide O atom on the one hand and to the equatorial carbonyl and carboxylic O atoms of two crystallographically independent niflumate moieties and their centrosymmetric counterparts on the other hand. In spite of the low-temperature (190 K) crystal measurements, one L-CF3 grouping exhibits some disorder. The biological activities of these complexes were compared to that of niflumic acid. Niflumic acid and its various copper complexes significantly inhibited polymorphonuclear leukocyte (PMNL) oxidative metabolism, as assessed by chemiluminescence and O2- generation measurement. This effect was dose-dependent. All copper complexes exerted a similar inhibiting effect which was always significantly higher than that exerted by the parent drug.

Animals↗
PubMed2003

Galactose-PEI-DNA complexes for targeted gene delivery: degree of substitution affects complex size and transfection efficiency.

Complexes of galactosylated polyethylenimines (gal-PEI) with DNA have been proposed for gene delivery to hepatocytes. We synthesized gal-PEI with a broad range of degrees of substitution (DS) ranging from 3.5 to 31% of all PEI amino groups by reductive amination to determine physico-chemical and biological properties with respect to the DS. Gel retardation assay for herring testes DNA-polymer polyplexes showed that increasing DS compromised DNA complexation and especially condensation. Using photon correlation spectroscopy, gal-PEI complexes formed with plasmid DNA were found to increase in size with increasing galactosylation (156+/-7 nm for 0%, 486+/-76 nm for 3.5%, 467+/-86 nm for 9.7% and 652+/-123 nm for 31% DS). Zeta potentials decreased in inverse proportion to DS (0%: 30+/-3 mV, 3.5%: 22+/-2 mV, 9.7%: 15+/-1 mV, 31%: -26+/-3.5 mV) suggesting a shielding effect by carbohydrate coupling. Cytotoxicity of gal-PEI was found to decrease with increasing galactosylation (MTT and LDH assay), no toxicity was detectable for polyplexes with plasmid DNA (LDH assay). The transfection efficiency of a reporter gene complexed with gal-PEI in a hepatocyte cell culture model (HepG2) expressing the asialoglycoprotein receptor was slightly but not significantly increased for galactosylated PEIs at a nitrogen to phosphate (N/P) ratio of 2 and strongly reduced at higher N/P ratios, compatible with only a minor targeting efficiency, strongly affected by DS. In NIH-3T3 mouse fibroblasts, increasing the DS led to a decreased transfection efficiency for all N/P ratios. Our study highlights the necessity of careful optimization of polyplex composition for active gene targeting.

3T3 Cells↗
PubMed1999

Human antibody responses to A and C capsular polysaccharides, IgA1 protease and transferrin-binding protein complex stimulated by infection with Neisseria meningitidis of subgroup IV-1 or ET-37 complex.

The protein sequences of the IgA1 protease, TbpA and TbpB proteins differ between meningococci representative of serogroup A, subgroup IV-1 from epidemic disease in The Gambia and serogroup C, ET-37 complex from endemic disease in Mali. The uniformity of restriction endonuclease sites was determined for the iga, tbpA and thpB genes among strains of both clonal lineages. Rare isolates had acquired a variant thpAB operon by horizontal genetic exchange but all other strains were uniform within each clonal lineage. The quantitative levels of IgG to capsular polysaccharide, IgA1 protease and TBP complex were measured in paired acute phase and convalescent phase sera from The Gambia and from Mali using antigens from the homologous clonal lineages. IgG levels to these antigens were also measured in paired sera from healthy Gambians who permanently carried meningococci in the nasopharynx or did not. The results showed that disease stimulated IgG to each antigen in Mali and to all but TBP complex in The Gambia. Similarly, higher levels of IgG were found in sera from permanent carriers than in sera from permanent non-carriers. Acute phase sera from Mali contained low levels of IgG to C capsular polysaccharide (geometric mean value of 0.3 microg ml(-1)) while such sera from The Gambia contained higher and potentially protective levels of IgG to A polysaccharide (geometric mean of 5.5 microg ml(-1)). The concentrations of IgG to TBP complex in acute phase sera were higher and IgG to IgA1 protease was even higher, suggesting that intermediate levels of IgG to these proteins do not protect against disease.

Amino Acid Sequence↗
PubMed1994

The Buford complex--the "cord-like" middle glenohumeral ligament and absent anterosuperior labrum complex: a normal anatomic capsulolabral variant.

Two hundred consecutive shoulder arthroscopy videotapes were retrospectively reviewed, paying specific attention to the anatomy of the anterosuperior glenoid quadrant and especially the labroligamentous complex. Normal glenohumeral anatomy and all variations were carefully evaluated and recorded. Twenty-four (12%) patients had a sublabral foramen below the anterosuperior labrum; a "cord-like" middle glenohumeral ligament was present in 75% (18 of 24) of those cases or 9% of the study population. A smaller group of patients demonstrated a unique variant of normal capsulolabral anatomy that, for convenience, is termed the "Buford complex." This unusual variant was noted in 3 of the 200 (1.5%) shoulders and was distinguished by a "cord-like" middle glenohumeral ligament that originated directly from the superior labrum at the base of the biceps tendon and crossed the subscapularis tendon to insert on the humerus. There was no anterior-superior labral tissue present between this attachment and the midglenoid notch. This unusual-appearing anatomical variation may lead the surgeon to confuse this complex with a sublabral hole or a pathologic labral detachment. The labral tissue of the remaining three glenoid quadrants was normal. If the Buford complex is mistakenly reattached to the neck of the glenoid, as illustrated in our case example, severe painful restriction of rotation and elevation will occur.

Acromioclavicular Joint↗
PubMed1996

Structure of the GDP-Pi complex of Gly203-->Ala gialpha1: a mimic of the ternary product complex of galpha-catalyzed GTP hydrolysis.

BACKGROUND: G proteins play a vital role in transmembrane signalling events. In their inactive form G proteins exist as heterotrimers consisting of an alpha subunit, complexed with GDP and a dimer of betagamma subunits. Upon stimulation by receptors, G protein alpha subunits exchange GDP for GTP and dissociate from betagamma . Thus activated, alphasubunits stimulate or inhibit downstream effectors. The duration of the activated state corresponds to the single turnover rate of GTP hydrolysis, which is typically in the range of seconds. In Gialpha1, the Gly203-->Ala mutation reduces the affinity of the substrate for Mg2+, inhibits a key conformational step that occurs upon GTP binding and consequently inhibits the release of betagamma subunits from the GTP complex. The structure of the Gly203-->Ala mutant of Gialpha1 (G203AGialpha1) bound to the slowly hydrolyzing analog of GTP (GTPgammaS) has been determined in order to elucidate the structural changes that take place during hydrolysis. RESULTS: We have determined the three dimensional structure of a Gly203-->Ala mutant of Gialpha1 at 2.6 A resolution. Although crystals were grown in the presence of GTPgammaS and Mg2+, the catalytic site contains a molecule of GDP and a phosphate ion, but no Mg2+. The phosphate ion is bound to a site near that occupied by the gamma-phosphate of GTPgammaS in the activated wild-type alpha subunit. A region of the protein, termed the Switch II helix, twists and bends to adopt a conformation that is radically different from that observed in other Gialpha1 subunit complexes. CONCLUSIONS: Under the conditions of crystallization, the Gly203-->Ala mutation appears to stabilize a conformation that may be similar, although perhaps not identical, to the transient ternary product complex of Gialpha1-catalyzed GTP hydrolysis. The rearrangement of the Switch II helix avoids a potential steric conflict caused by the mutation. However, it appears that dissociation of the gamma-phosphate from the pentacoordinate intermediate also requires a conformational change in Switch II. Thus, a conformational rearrangement of the Switch II helix may be required in Galpha-catalyzed GTP hydrolysis.

Alanine↗
PubMed2002

Use of the ion exchange method for the determination of stability constants of trivalent metal complexes with humic and fulvic acids--part I: Eu3+ and Am3+ complexes in weakly acidic conditions.

The conditional stability constants for tracer concentrations of Eu(III) and Am(III) with a red earth humic acid (REHA), a red earth fulvic acid (REFA) and a fulvic acid from weathered coal (WFA) were determined at pH 5.2-6.4 (such values are similar to those in non-calcareous soils) in the presence of HAc/NaAc or NaNO3 by using the cation exchange method. It was found that 1:1 complexes were predominately formed in weakly acidic conditions. The total exchangeable proton capacities and the degrees of dissociation of these humic substances were determined by using a potentiometric titration method. The key parameters necessary for the experimental determination of the conditional stability constants of metal ions with humic substances in weakly acidic conditions by using the cation exchange method were discussed. The conditional stability constants of 1:1 complexes obtained in this paper were compared with the literature data of Am(III) determined by using the ion exchange method and the solvent extraction method and with the stability constants of 1:1 complexes of UO2(2+) and Th4+ with the same soil humic substances. These results indicate the great stability of bivalent UO2(2+), trivalent Eu3+, Am3+ and tetravalent Th4+ complexes with humic and fulvic acids in weakly acidic conditions.

Journal Article↗
PubMed2000

Spectroscopic studies of some novel CuI and CuII complexes derived from the tribochemistry reactions of Kbr, KI and CaI2 with CuII-Girard's T complex [Cu(GT)Cl2(H2O)2(EtOH)]Cl.H2O.

Novel CuI and CuII complexes derived from the tribochemistry reactions of [Cu(GT)Cl2(H2O)2(EtOH)Cl.H2O with KBr, KI and CaI2 have been isolated and characterized. The reactions of KI and CaI2 with [Cu(GT)Cl2(H2O)2(EtOH)]Cl.H2O in the solid state are accompanied by colour change, reduction of CuII to CuI and substitution of the chloride by iodide ions. Also, the tribochemistry reaction of KBr with the CuII-GT complex is accompanied by change in colour, substitution of chloride by bromide ions but no reduction has been occurred. All the isolated solid complexes have been characterised by spectral (UV-vis, IR, 1H-NMR), magnetic and thermal measurements. The effect of the variation of the ratio between alkali and/or alkaline earth metal halides (KI, KBr, and CaI2) and the CuII-GT complex has also been investigated.

Betaine↗
PubMed2001

Metal complexes of antibiotic drugs. Studies on dicluxacillin complexes of FeII, FeIII, CoII NiII and CuII.

The synthesis and characterization of dicluxacillin (DC) complexes with di- and tri-valent metal ions are described. The nature of bonding of the chelated DC and its metal complexes structures have been elucidated on the basis of their spectroscopic (infrared, solid reflectance, magnetic spectra, mass and thermal analysis) properties. In all the complexes studied, the DC acts as a chelate monoanionic ligand with coordination involving the carboxylate O atom and the endocyclic N of the thiazole ring. The DC ligand forms mono-ligand complexes of the general formula [M(DC)(H2O)x(A)]. yH2O where DC is the uninegatively charged bidentate ligand and A = OAc in case of CuII and Cl in case of FeIII, FeII, CoII and NiII ions. IR, solid reflectance spectra and magnetic moment measurement are used to infer the structure and to illustrate the coordinating capacity of the ligand. From the thermal decomposition curves, the water molecules of crystallization are removed in a single stage while the decomposition of the ligand and coordinated water molecules occur in the second and subsequent stages. Different thermodynamic kinetic parameters namely activation energy (E*), enthalpy of activation (AH*), entropy of activation (AS*) and free energy change of activation (AG*) are calculated using Coats and Redfern equation.

Anti-Bacterial Agents↗
PubMed2001

The Sec34/35 Golgi transport complex is related to the exocyst, defining a family of complexes involved in multiple steps of membrane traffic.

The specificity of intracellular vesicle transport is mediated in part by tethering factors that attach the vesicle to the destination organelle prior to fusion. We have identified a protein, Dor1p, that is involved in vesicle targeting to the yeast Golgi apparatus and found it to be associated with seven further proteins. Identification of these revealed that they include Sec34p and Sec35p, the two known components of the Sec34/35 complex previously proposed to tether vesicles to the Golgi. Of the six previously uncharacterized components, four have homologs in higher eukaryotes, including a subunit of a mammalian Golgi transport complex. Furthermore, several of the proteins show distant homology to components of two other putative tethering complexes, the exocyst and the Vps52/53/54 complex, revealing that tethering factors involved in different membrane traffic steps are structurally related.

Adaptor Proteins, Vesicular Transport↗
PubMed2006

Roles of metal ion complexation and membrane permeability in the metal flux through lipophilic membranes. Labile complexes at permeation liquid membranes.

The various physicochemical factors that influence the flux of carrier-transported metal ions through permeation liquid membranes (PLM) are studied systematically. Understanding PLM behavior is important (i) to optimize the application of PLM as metal speciation sensors in environmental media and (ii) because PLM may serve as bioanalogical devices that help to elucidate the environmental physicochemical processes occurring at the surface of biological membranes. Diffusion of free and complexed metal ions in solution, as well as diffusion of the metal carrier complex in the membrane, is considered. The respective roles of diffusion layer thickness, ligand concentration, complex stability, carrier concentration, and membrane thickness are studied experimentally in detail and compared with theory, using various labile complexes, namely, Pb(II)-diglycolate, Cu(II)-diglycolate, and Cu(II)-N-(2-carboxyphenyl)glycine. Conditions where either membrane diffusion or solution diffusion is rate limiting are clearly discriminated. It is shown in particular, that, by tuning the carrier concentration or membrane thickness, either the free metal ion concentration or the total labile metal species are measured. PLM can thus be used to determine whether models based on the free ion activity in solution (such as BLM or FIAM models) are applicable to metal uptake by microorganisms in a real natural medium.

Journal Article↗
PubMed2000

Effects of compound structure on carbazole dication-DNA complexes: tests of the minor-groove complex models.

Carbazole dications have shown excellent activity against opportunistic infections, but they are quite different in structure from previously studied unfused aromatic cations that function by targeting the DNA minor groove. In a previous report [Tanious, F. A., Ding, D., Patrick, D. A., Tidwell, R. R., and Wilson, W. D. (1997) Biochemistry 36, 15315-15325] we showed that, despite their fused ring structure, the carbazoles also bind in A/T sequences of the DNA minor groove and we proposed models for the carbazole-DNA complexes with the carbazole nitrogen facing out of the groove for 3,6 substituted compounds but into the groove in 2,7 carbazoles. To test and refine the models, carbazole-N-methyl substituted derivatives have been synthesized in both the 3,6 and 2,7 series as well as a new 2,6 substituted NH derivative that is intermediate in structure. Footprinting results indicate a broad AT specificity of carbazole binding and a pattern in agreement with a minor groove complex. Surface plasmon resonance biosensor analysis of carbazole binding to an oligomer with an AATT central sequence indicated that the 2,7 NH compound has the largest binding constant. Both the 3,6 NH and NMe compounds bind with similar equilibrium constants that are less than for the 2,7 NH compound. The 2,7 NMe compound has the lowest binding constant of all the carbazoles. Spectroscopic results are also similar for the two 3,6 derivatives but are quite different for the 2,7 NH and NMe carbazole dications. Structural analysis of carbazole complexes with an AATT sequence by 2D NMR methods also supported a minor groove complex of the carbazoles in orientations in agreement with the previously proposed models. From these results, it is clear that the fused ring carbazoles can bind strongly in the DNA minor groove with a broad A/T specificity and that the 2,7 and 3,6 substituted carbazoles bind to the minor groove in opposite orientations.

Binding Sites↗
PubMed1992

A heat shock protein complex isolated from rabbit reticulocyte lysate can reconstitute a functional glucocorticoid receptor-Hsp90 complex.

When unliganded glucocorticoid receptor that has been stripped free of associated proteins is incubated with rabbit reticulocyte lysate, the receptor becomes associated with the 70- and 90-kDa heat shock proteins (hsp70 and hsp90), and the untransformed state of the receptor is functionally reconstituted [Scherrer, L. C., Dalman, F. C., Massa, E., Meshinchi, S., & Pratt, W. B. (1990) J. Biol. Chem. 265, 21397-21400]. Recently, an hsp70-containing protein complex (200-250 kDa) purified from rabbit reticulocyte lysate was shown to maintain a fusion protein bearing the mitochondrial matrix-targeting signal in a state that is competent for mitochondrial import [Sheffield, W. P., Shore, G. C., & Randall, S. K. (1990) J. Biol. Chem. 265, 11069-11076]. In this work, we show that this partially purified mitochondrial import-competent fraction contains both hsp90 and hsp70. When the purified fraction is immunoadsorbed with a monoclonal antibody specific for hsp90, a significant portion of the hsp70 is co-immunoadsorbed, suggesting that hsp90 and hsp70 are present together as a complex. The partially purified fraction maintains a hybrid precursor protein containing the mitochondrial matrix-targeting signal of rat pre-ornithine carbamyl transferase in an import-competent state. Incubation of immunopurified glucocorticoid receptor with this fraction of reticulocyte lysate results in ATP-dependent association of the receptor with both hsp70 and hsp90, and the resulting complexes are functional as assessed by return of the receptor to the high-affinity steroid binding conformation. The glucocorticoid receptor hetero-complex reconstituting activity of the lysate fraction is low relative to its mitochondrial import activity. Importantly, however, this is the first demonstration of the functional and structural reconstitution of the untransformed state of any steroid receptor utilizing a partially purified system.

Animals↗
PubMed1994

Crystal structures of wild-type p-hydroxybenzoate hydroxylase complexed with 4-aminobenzoate,2,4-dihydroxybenzoate, and 2-hydroxy-4-aminobenzoate and of the Tyr222Ala mutant complexed with 2-hydroxy-4-aminobenzoate. Evidence for a proton channel and a new binding mode of the flavin ring.

The crystal structures of wild-type p-hydroxybenzoate hydroxylase from Pseudomonas fluorescens, complexed with the substrate analogues 4-aminobenzoate, 2,4-dihydroxybenzoate, and 2-hydroxy-4-aminobenzoate have been determined at 2.3-, 2.5-, and 2.8-A resolution, respectively. In addition, the crystal structure of a Tyr222Ala mutant, complexed with 2-hydroxy-4-aminobenzoate, has been determined at 2.7-A resolution. The structures have been refined to R factors between 14.5% and 15.8% for data between 8.0 A and the high-resolution limit. The differences between these complexes and the wild-type enzyme-substrate complex are all concentrated in the active site region. Binding of substrate analogues bearing a 4-amino group (4-aminobenzoate and 2-hydroxy-4-aminobenzoate) leads to binding of a water molecule next to the active site Tyr385. As a result, a continuous hydrogen-bonding network is present between the 4-amino group of the substrate analogue and the side chain of His72. It is likely that this hydrogen-bonding network is transiently present during normal catalysis, where it may or may not function as a proton channel assisting the deprotonation of the 4-hydroxyl group of the normal substrate upon binding to the active site. Binding of substrate analogues bearing a hydroxyl group at the 2-position (2,4-dihydroxybenzoate and 2-hydroxy-4-aminobenzoate) leads to displacement of the flavin ring from the active site. The flavin is no longer in the active site (the "in" conformation) but is in the cleft leading to the active site instead (the "out" conformation). It is proposed that movement of the FAD out of the active site may provide an entrance for the substrate to enter the active site and an exit for the product to leave.

4-Aminobenzoic Acid↗
PubMed1993

11B NMR spectroscopy of peptide boronic acid inhibitor complexes of alpha-lytic protease. Direct evidence for tetrahedral boron in both boron-histidine and boron-serine adduct complexes.

We have previously shown, using 15N and 1H NMR spectroscopy, that MeOSuc-Ala-Ala-Pro-boroPhe and certain other boronic acid inhibitors form boron-histidine adducts with alpha-lytic protease instead of transition-state-like tetrahedral boron-serine adducts as is generally supposed [Bachovchin, W. W., Wong, W. Y. L., Farr-Jones, S., Shenvi, A. B., & Kettner, C. (1988) Biochemistry 27, 7689-7697]. An X-ray crystallographic study of the MeOSuc-Ala-Ala-Pro-boroPhe complex with alpha-lytic protease [Bone, R., Frank, D., Kettner, C. A., & Agard, D. A. (1989) Biochemistry 28, 7600-7609] has confirmed the existence of the boron-histidine bond but has concluded that the boron atom is trigonal rather than tetrahedral. Here we report a 11B NMR study at 160.46 MHz of this histidine adduct complex and of two other complexes known to be serine adducts: alpha-lytic protease with MeOSuc-Ala-Ala-Pro-boroVal and chymotrypsin with MeOSucAla-Ala-Pro-boroPhe. The 11B NMR chemical shifts demonstrate that the boron atom is tetrahedral in both the histidine and serine adduct complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Structural study of porcine pancreatic elastase complexed with 7-amino-3-(2-bromoethoxy)-4-chloroisocoumarin as a nonreactivatable doubly covalent enzyme-inhibitor complex.

The complex of porcine pancreatic elastase (PPE) with 7-amino-3-(2-bromoethoxy)-4-chloroisocoumarin, a potent mechanism-based inhibitor, was crystallized and the crystal structure determined at 1.9-A resolution with a final R factor of 17.1%. The unbiased difference Fourier electron density map showed continuous density from O gamma of Ser 195 to the benzoyl carbonyl carbon atom and from N epsilon 2 of His 57 to the carbon atom at the 4-position of the isocoumarin ring in the inhibitor. This suggested unambiguously that the inhibitor was doubly covalently bound to the enzyme. It represents the first structural evidence for irreversible binding of an isocoumarin inhibitor to PPE through both Ser 195 and His 57 in the active site. The PPE-inhibitor complex is only partially activated in solution by hydroxylamine and confirms the existence of the doubly covalently bound complex along with the acyl enzyme. The benzoyl carbonyl oxygen atom of the inhibitor is not situated in the oxyanion hole formed by the amide (greater than NH) groups of Gly 193 and Ser 195. The complex is stabilized by the hydrogen-bonding interactions in the active site (from the N epsilon 2 of Gln 192 to the bromine atom in the inhibitor and the amino group at the 7-position of the isocoumarin ring to the carbonyl oxygen of Thr 41) and by van der Waals interactions. The inhibition rates of several 7-substituted 4-chloro-3-(bromoalkoxy)isocoumarins toward PPE were measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1982

Effects of solvent on the absorption maxima of five-coordinate heme complexes and carbon monoxide-heme complexes as models for the differential spectral properties of hemoglobins and myoglobins.

Absorption spectra were recorded for 5- and 6-coordinate model ferrous heme complexes of hindered and unhindered ligands in aqueous, and detergent solutions. Heme complexes exhibited differences in absorption maxima up to 6 nm which were correlated with the polarity of the heme environment. Increasing polarity of the solvent resulted in a general blue shift of absorption maxima of both deoxy- and (carbon monoxy)heme complexes. The differences in absorption maxima of heme complexes with different heme environments are offered as a possible explanation for some of the differences in absorption maxima among hemoproteins such as hemoglobin, myoglobin, and leghemoglobin.

Carbon Monoxide↗
PubMed1977

Actinomycin D complexes with oligonucleotides as models for the binding of the drug to DNA. Paramagnetic induced relaxation experiments on drug-nucleic acid complexes.

Mn(II) ions have been used as a paramagnetic probe to investigate the geometry of drug-oligonucleotide complexes. Nuclear magnetic resonance and electron spin resonance experiments show that Mn(II) ions bind approximately two orders of magnitude stronger to the 5'-terminal phosphate group than to the 3'-5' phosphodiester linkage of deoxydinucleotides. By using mixtures of nucleotides in which only one nucleotide contains a terminal phosphate group, the location of the Mn(II) ion in the drug-nucleotide-Mn(II) complexes may be preselected. The paramagnetic induced relaxation of the nuclear spin systems in these complexes has been used to investigate the geometry of these complexes. These data confirm that actinomycin D is able to recognize and preferentially bind guanine (as opposed to adenine) nucleotides in the quinoid portion of the phenoxazone ring, while both adenine and guanine will bind to the benzenoid portion of the phenoxazone ring. These results suggest that stacking forces are primarily responsible for the general requirement of a guanine base when actinomycin D binds to DNA.

Binding Sites↗
PubMed1999

NMR structure of the complex between the zinc finger protein NCp10 of Moloney murine leukemia virus and the single-stranded pentanucleotide d(ACGCC): comparison with HIV-NCp7 complexes.

The structure of the 56 amino acid nucleocapsid protein NCp10 of retrovirus MoMuLV, which contains a single CX(2)CX(4)HX(4)C-type zinc finger, has been determined previously by NMR. The important role of NCp10 (or NCp7 for HIV-1) in the retroviral life cycle seems mainly related to their preferential binding to single-stranded nucleic acids. We report here the structure of the complex formed between the biologically active (14-53)NCp10 and the oligonucleotide d(ACGCC) in aqueous solution determined by 2D (1)H NMR based methods. The aromatic residue Trp(35) of NCp10 directs nucleic acid complexation as shown by its complete fluorescence quenching upon addition of d(ACGCC). (1)H and (31)P NMR studies support the insertion of Trp(35) between the G(3) and C(4) bases. A total of 577 NOE distance restraints, of which 40 were intermolecular, were used for the structure determination. The zinc finger provides a well-defined surface for the binding of d(ACGCC) through hydrophobic interactions and tryptophan stacking on the guanine. This latter interaction was also observed in the NMR-derived structures of the complexes between NCp7, which contains two successive zinc fingers, and single-stranded DNA and RNA, supporting the proposal for a major role played by aromatic residues of NCp proteins in nucleic acid recognition. Upon binding to the nucleotide a new loop in NCp10 that participates in the intermolecular interaction is formed. Additional interactions provided by positively charged residues surrounding the zinc finger appear necessary for tight binding. The structure of the complex NCp10-d(ACGCC) gives a structural explanation for the loss of virus infectivity following point mutations in the finger domain.

Amino Acid Sequence↗