Enhancement of aromatic amino acid-nucleic acid base stacking interaction by metal coordination to base: fluorescence study on a tryptophan-Pt(II)-guanine ternary complex

Interaction of Natural Compounds in Licorice and Turmeric with HIV-NCp7 Zinc Finger Domain: Potential Relevance to the Mechanism of Antiviral Activity

Nucleocapsid proteins (NCp) are zinc finger (ZF) proteins, and they play a central role in HIV virus replication, mainly by interacting with nucleic acids. Therefore, they are potential targets for anti-HIV therapy. Natural products have been shown to be able to inhibit HIV, such as turmeric and licorice, which is widely used in traditional Chinese medicine. Liquiritin (LQ), isoliquiritin (ILQ), glycyrrhizic acid (GL), glycyrrhetinic acid (GA) and curcumin (CUR), which were the major active components, were herein chosen to study their interactions with HIV-NCp7 C-terminal zinc finger, aiming to find the potential active compounds and reveal the mechanism involved. The stacking interaction between NCp7 tryptophan and natural compounds was evaluated by fluorescence. To elucidate the binding mode, mass spectrometry was used to characterize the reaction mixture between zinc finger proteins and active compounds. Subsequently, circular dichroism (CD) spectroscopy and molecular docking were used to validate and reveal the binding mode from a structural perspective. The results showed that ILQ has the strongest binding ability among the tested compounds, followed by curcumin, and the interaction between ILQ and the NCp7 zinc finger peptide was mediated by a noncovalent interaction. This study provided a scientific basis for the antiviral activity of turmeric and licorice.

Dinuclear platinum complexes containing planar aromatic ligands to enhance stacking interactions with proteins

In an approach to design drugs with higher affinity for π-π stacking and electrostatic interactions with targeted biomolecules, complexes of the type [{cis-Pt(A)2 (L)}2 -μ-{trans-1,4-dach}](NO3 )4 ((A)2 =(NH3 )2 or ethylenediamine (en), L=quinoline (quin) or benzothiazole (bztz), dach=trans-1,4-diaminocyclohexane) were synthesized. The quinoline complex, [{cis-Pt(en)(quin)}2 -μ-(dach)](NO3 )4 (9) was synthesized from the precursor K[PtCl3 (quin)] (1), while the benzothiazole complexes, [{cis-Pt(A)2 (bztz)}2 -μ-(dach)](NO3 )4 ((A)2 =(NH3 )2 (10) and (A)2 =en (11)) were synthesized from the precursors cis-[Pt(A)2 Cl(bztz)] ((A)2 =(NH3 )2 (7) and (A)2 =en (8)). Their interactions with N-acetyltryptophan and a model pentapeptide (N-Ac-WLDSW-OH), modeled on the pentapeptide recognition sequence (FSDLW) of p53-mdm2 interaction, were examined by fluorescence spectroscopy. The dinuclear complexes were found to be significantly stronger at quenching the fluorescence of tryptophan than their mononuclear Pt-based analogues indicating stronger binding. Molecular modeling suggests a "sandwich" mode of binding, and the flexibility of the dinuclear motif can allow the design of more selective and stronger-binding complexes. Based on these results a further prototype, [{Pt(en)(9-EtGua)}2 μ-H2 N(CH2 )6 NH2 ](4+) , incorporating the purine 9-ethylguanine (9-EtG) as a stacking moiety, was prepared which showed good cytotoxicity in A2780 and OsACL tumor cell lines.

Structural studies of specific intermolecular interactions and self-aggregation of biomolecules and their application to drug design

Information on the structural basis of intermolecular recognition or self-aggregation of biomolecules at the atomic level is important to understand biological functions and to develop devices for treating disorders caused by abnormal functions. Thus structural analysis of specific intermolecular or intramolecular interactions of biomolecules has been performed using various physicochemical approaches. Herein, the following three subjects are reviewed: (1) structural analyses of mRNA cap structure recognition by eukaryotic initiation factor 4E and its functional regulation by endogenous 4E-binding protein; (2) structural studies of self-aggregation mechanism of microtubule-binding domain in tau protein and aggregation inhibitor; and (3) molecular design of cathepsin B-specific inhibitor.

Platination of nucleobases to enhance noncovalent recognition in protein-DNA/RNA complexes

Fluorescence quenching experiments show that the stacking interaction between nucleic acid bases and l-tryptophan is enhanced significantly upon base coordination to a metal center such as Pt(II), and the biological implications of such enhancement are discussed.

Inversion of the cis geometry requirement for cytotoxicity in structurally novel platinum(II) complexes containing the bidentate N,O-donor pyridin-2-yl-acetate

Water soluble platinum(II) complexes have been synthesized that contain the N,O-chelate pyridin-2-yl acetate (PyAc) as a novel structural motif in platinum antitumor complexes. The trans-platinum complex trans-[PtCl(PyAc-N,O)(NH3)] (2) (N-donors are trans) and its isomer cis-[PtCl(PyAc-N,O)(NH3)] (4) (N trans to Cl) were prepared from trans-[PtCl2((NH3)(PyAcH)].H2O (1.H2O) and cis-[PtCl2(NH3)(PyAcMe) (3), respectively, employing the bidentate ligand as its methylester (PyAcMe). 2 and 4 are readily formed from the respective dichloro species, even at low pH and in the presence of extra chloride, indicating a high thermodynamic stability of the PyAc chelate ring. 1.H2O and 2-4 were characterized by 1H NMR and IR spectroscopy and elemental analyses. The solid-state structure of 2 was determined: triclinic, P1 (no. 2), with a = 8.170(2) A, b = 9.274(3) A, c = 7.374(2) A, alpha = 108.68(2) degrees, beta = 113.27(2) degrees, gamma = 74.40(2) degrees, V = 479.7(6) A3, Z = 2. The six-membered metallacyclus in 2 adopts a "boat" form, allowing a strainless coordination of platinum. The most promising cytotoxic properties in the above series of compounds have been established for 2 (and 1, which rapidly transforms into 2 at 37 degrees C and neutral pH). Preliminary ID50 values were 0.88 and 1.26 microM, respectively, in cisplatin-sensitive L1210 leukemia. Both compounds proved to be cross-resistant to the clinical drug. Reactions of 2 and 4 with 5'-guanosine monophosphate (5'-GMP) under physiological conditions gave the monofunctional adducts trans- and cis-[Pt(5'-GMP-N7)(PyAc-N,O)(NH3)] (I and II). Chelate-bound carboxylate was not replaced by guanine-N7 when an excess of nucleotide was applied (NMR). In an analogous reaction, 2 reacts with the oligonucleotide d(TCGT) [5'-T(1)-C(2)-G(3)-T(4)-3'] to give the adduct d(TCGT)-N7(3)-Pt(PyAc-O,N)(NH3) (III), which was characterized by a combination of total correlation spectroscopy, double-quantum-filtered correlation spectroscopy, nuclear Overhauser effect spectrometry, and rotating-frame Overhauser enhancement spectroscopy experiments. Binding of the [Pt(PyAc-N,O)(NH3)]+ fragment to N7 of G(3) causes an increase of N-type character of the T(4) and G(3) deoxyribose residues relative to the unplatinated sequence, while those of T(1) and C(2) remain S-type. An internucleotide nuclear Overhauser effect between H6(4) and H2'(3) indicates stacking between guanine and the 3'-thymine base. The most striking feature proved to be the pronounced upfield shift and broadening of the 1H NMR signals assigned to the base protons H5 and H6 in III. Magnetization transfer between H5(2) and H3 of pyridine suggests that this effect is caused by base-base interactions involving the planar ligand on platinum, which must be situated on the 5' face of guanine. Possible implications for the DNA binding and cytotoxic effect of the compounds are discussed.

Synthesis, Structure, Biological Activity, and DNA Binding of Platinum(II) Complexes of the Type trans-[PtCl(2)(NH(3))L] (L = Planar Nitrogen Base). Effect of L and Cis/Trans Isomerism on Sequence Specificity and Unwinding Properties Observed in Globally Platinated DNA

In order to establish fundamental structural requirements for the antitumor activation of the trans-platinum geometry, complexes of the general formulas [PtCl(2)(NH(3))L] (L = planar N donor) have been synthesized. The trans isomers, trans-[PtCl(2)(NH(3))(quinoline)] (3), trans-[PtCl(2)(NH(3))(thiazole)] (5), trans-[PtCl(2)(NH(3))(benzothiazole)] (7), and trans-[PtCl(2)(NH(3))(isoquinoline)] (8) and the cis isomers cis-[PtCl(2)(NH(3))(quinoline)] (4) and cis-[PtCl(2)(NH(3))(thiazole)] (6) were characterized by (1)H NMR and analytical data. In addition, the crystal structures of 3, 5, 7, and 8 were determined: 3, monoclinic, P2(1)/c, with a = 8.414(1) Å, b = 12.373(3) Å, c = 21.266(3) Å, beta = 96.78(1) degrees, V = 2198.3(6) Å(3), and Z = 8; 5, monoclinic, P2(1)/n, with a = 8.815(4) Å, b = 19.917(8) Å, c = 14.498(5) Å, beta = 103.30(3) degrees, V = 2477(2) Å(3), and Z = 12; 7, monoclinic, P2(1)/c, with a = 8.150(4) Å, b = 23.196(9) Å, c = 11.297(7) Å, beta = 90.94(4) degrees, V = 2135.3(2) Å(3), and Z = 8; 8, monoclinic, C2/c, with a = 19.043(4) Å, b = 8.570(2) Å, c = 29.127(6) Å, beta_ = 111.59(2) degrees, V = 4420(2) Å(3), and Z = 16. In all cases, the Pt coordination plane and L are mutually twisted with angles between planes of 50-68 degrees. Bulky quinoline in 3 produces intramolecular steric strain as evidenced by a short, nonbonding Pt.H8(quin) contact of 2.77 Å and concomitantly distorted Pt-N(quin)-C bond angles. The trans complexes 3, 5, 7, and 8 showed a significantly higher cytotoxicity in cisplatin-sensitive L1210 leukemia than trans-[PtCl(2)(NH(3))(2)] (2), with 3 and 5 being as potent as the corresponding cis isomers 4 and 6. In addition, the presence of the planar ligand greatly enhanced the activity of all of the compounds in cells resistant to cisplatin, cis-[PtCl(2)(NH(3))(2)] (1). Complex geometry and L play an important role in the binding of 1-7 to DNA. For synthetic poly(dG).poly(dC) and poly(dG-dC).poly(dG-dC) the order of binding affinities (r(b), drug-to-nucleotide ratio) was 2 > 1 > 6 > 5 > 4 > 7 > 3 and 5 > 6 > 7 > 3 > 2 > 1 > 4, respectively. Furthermore, 3 and 7, carrying large planar ligands, were remarkably effective at unwinding negatively supercoiled, closed circular pUC19 DNA (phi = 15 degrees and 17 degrees, respectively). The consequences of structural effects caused by L on target DNA with respect to possible biological consequences are discussed.