The thrombin binding aptamer (TBA) is a promising nucleic acid-based anticoagulant. We studied the effects of chemical modifications, such as dendrimer Trebler and NHS carboxy group, on TBA with respect to its structures and thrombin binding affinity. The two dendrimer modifications were incorporated into the TBA at the 5′ end and the NHS carboxy group was added into the thymine residues in the thrombin binding site of the TBA G-quadruplex (at T4, T13 and both T4/T13) using solid phase oligonucleotide synthesis. Circular dichroism (CD) spectroscopy confirmed that all of these modified TBA variants fold into a stable G-quadruplex. The binding affinity of TBA variants with thrombin was measured by surface plasmon resonance (SPR). The binding patterns and equilibrium dissociation constants (KD) of the modified TBAs are very similar to that of the native TBA. Molecular dynamics simulations studies indicate that the additional interactions or stability enhancement introduced by the modifications are minimized either by the disruption of TBA–thrombin interactions or destabilization elsewhere in the aptamer, providing a rational explanation for our experimental data. Overall, this study identifies potential positions on the TBA that can be modified without adversely affecting its structure and thrombin binding preference, which could be useful in the design and development of more functional TBA analogues. 相似文献
The molybdenum cofactor (Moco) is the active site prosthetic group found in numerous vitally important enzymes (Mo-enzymes), which predominantly catalyze 2 electron transfer reactions. Moco is synthesized by an evolutionary old and highly conserved multi-step pathway, whereby the metal insertion reaction is the ultimate reaction step here. Moco and its intermediates are highly sensitive towards oxidative damage and considering this, they are believed to be permanently protein bound during synthesis and also after Moco maturation. In plants, a cellular Moco transfer and storage system was identified, which comprises proteins that are capable of Moco binding and release but do not possess a Moco-dependent enzymatic activity. The first protein described that exhibited these properties was the Moco carrier protein (MCP) from the green alga Chlamydomonas reinhardtii. However, MCPs and similar proteins have meanwhile been described in various plant species. This review will summarize the current knowledge of the cellular Moco distribution system. 相似文献
A new colorimetric recognition receptor 1 based on the dual capability containing NH binding sites of selectively sensing anionic guest species has been synthesized. Compared with other halide anions, its UV/Vis absorption spectrum in dimethyl sulfoxide showed the response toward the presence of fluoride anion with high selectivity, and also displayed dramatic color changes from colorless to yellow in the presence of TBAF (5 × 10^-5 mol/L). The similar UV/Vis absorption spectrum change also occurred when 1 was treated with AcO^- while a little change with H2PO^-4 and OH^-. Receptor 1 has almost not affinity abilities to Cl^-, Br^- and I^-. The binding ability of receptor 1 to fluoride with high selectivity over other halides contributes to the anion size and the ability of forming hydrogen bonding. While the different ability of binding with geometrically triangular (AcO^-), tetrahedral (H2PO^-4 ) and linear (OH^-) anions maybe result from their geometry configuration. 相似文献
Bound together : The association of receptors with ionic species cannot be assimilated to the binding of neutral guests. When dealing with salts, both ion pairing and binding to the free and the ion‐paired ionic guest determine the actual association pattern (see figure). The general issue of measuring association constants and assessing affinities for ions is addressed and validated in two cases of anion binding.
The binding properties of granular alginic acid(H-alg.) and chitin to iodine, bromine, cadmium ion, calcium ion and cholesterol were investigated. Chitin-iodine and chitin-bromine compounds closely resemble those of H-alg. The amount of iodine included by these polysaccharides increased with a decrease in the concentration of potassium iodide (KI). The number of sugar residues bound to one iodine molecule extrapolated to 0 g of KI was around 6.0 for H-alg. and 6.4 for chitin. These saccharides, which do not form a gel in water, were found to also absorb KI and radioactive iodide or iodine in aqueous solution. H-alg. did not show as much affinity to cadmium ion and calcium ion and cholesterol in iso-propyl alcohol as metalalginates.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986. 相似文献
The synthesis of a new triaminoguanidinium-based ligand with three tris-chelating [NNO]-binding pockets and C3 symmetry is described. The reaction of tris-(2-pyridinylene-N-oxide)triaminoguanidinium salts with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds which in solution bind fullerenes in their spherical cavities. The rapid encapsulation of C60 can be observed by NMR spectroscopy and single-crystal X-ray diffraction and is verified using computation. 相似文献
Complexation and protonation equilibria were studied in aqueous solution for a new range of aminocryptand ligands, N(CH2CH2NHCH2RCH2NHCH2CH2)3N, (R = m-xylyl, p-xylyl, 2,5-furan, 2,6-pyridine) and demonstrate that stability constants for first transition series ions Co2+ to Zn2+ are relatively high. X-ray crystallography shows that the cryptands are reasonably well preorganized for complexation. The furan-spaced cryptand L6.H2O crystallizes in the rhomobohedral space group R3 (no. 148) with a = 14.645(1), b = 14.645(1), and c = 25.530(4) A, whereas the m-xylyl-spaced cryptand L4 crystallizes in the triclinic space group P1 (no. 2) with a = 9.517(1), b = 15.584(2), and c = 23.617(4) A. The highest formation constant (log beta21 = 33.07) is observed for the dicopper cryptate of a pyridine-spaced cryptand, suggesting involvement in complexation of donors from the spacer link. This pyridine-spaced host also shows good selectivity for copper(II) over zinc(II), making it a possible candidate for treatment of copper-excess pathology. 相似文献
Fatty acid binding proteins are responsible for the transportation of fatty acids in biology. Despite intensive studies, the molecular mechanism of fatty acid entry to and exit from the protein cavity is still unclear. Here a cap‐closed variant of human intestinal fatty acid binding protein was generated by mutagenesis, in which the helical cap is locked to the β‐barrel by a disulfide linkage. Structure determination shows that this variant adopts a closed conformation, but still uptakes fatty acids. Stopped‐flow experiments indicate that a rate‐limiting step exists before the ligand association and this step corresponds to the conversion of the closed form to the open one. NMR relaxation dispersion and H‐D exchange data demonstrate the presence of two excited states: one is native‐like, but the other adopts a locally unfolded structure. Local unfolding of helix 2 generates an opening for ligands to enter the protein cavity, and thus controls the ligand association rate. 相似文献
Synthetic carbohydrate receptors (SCRs) that selectively recognize cell-surface glycans could be used for detection, drug delivery, or as therapeutics. Here we report the synthesis of seven new C2h symmetric tetrapodal SCRs. The structures of these SCRs possess a conserved biaryl core, and they vary in the four heterocyclic binding groups that are linked to the biaryl core via secondary amines. Supramolecular association between these SCRs and five biologically relevant C1-O-octyloxy glycans, α/β-glucoside ( α/β-Glc ), α/β-mannoside ( α/β-Man ), and β-galactoside ( β-Gal ), was studied by mass spectrometry, 1H NMR titrations, and molecular modeling. These studies revealed that selectivity can be achieved in these tetrapodal SCRs by varying the heterocyclic binding group. We found that SCR017 (3-pyrrole), SCR021 (3-pyridine), and SCR022 (2-phenol) bind only to β-Glc. SCR019 (3-indole) binds only to β-Man. SCR020 (2-pyridine) binds β-Man and α-Man with a preference to the latter. SCR018 (2-indole) binds α-Man and β-Gal with a preference to the former. The glycan guests bound within their SCR hosts in one of three supramolecular geometries: center-parallel, center-perpendicular, and off-center. Many host–guest combinations formed higher stoichiometry complexes, 2:1 glycan⋅SCR or 1:2 glycan⋅SCR , where the former are driven by positive allosteric cooperativity induced by glycan–glycan contacts. 相似文献
Binding of zonisamide, a new antiepileptic sulfonamide derivative, was examined to human erythrocytes, their lysate and their carbonic anhydrase by centrifugation for cells or by ultrafiltration for the others. Scatchard plots revealed that the binding to intact and lysed cells was composed of high- and low-affinity components and that to carbonic anhydrase, of the high-affinity component alone. Parameters for high-affinity binding were similar in all three preparations and those for low-affinity binding were similar in the former two preparations. Dissociation constants for these bindings to erythrocytes were smaller than the dissociation constant for serum albumin. These results may explain the concentration of sulfonamides in red cells, and suggest the participation of cellular protein component(s) in addition to previously known carbonic anhydrase in the binding. Acetazolamide, sulthiame, zonisamide, hydrochlorothiazide and sulfanilamide inhibited carbonic anhydrase in a non-competitive manner to different extents. The Ki values of these sulfonamides were of the order of 0.1--0.2 of their respective Kd values determined by ultrafiltration, suggesting that under the present conditions, physicochemical interactions between sulfonamides and carbonic anhydrase primarily occur at common sites that affect the activity of the enzyme. 相似文献