脲和盐酸胍诱导的牛碳酸酐酶B的去折叠

采用非变性聚丙烯酰胺凝胶电泳、十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、高效凝胶排阻色谱和激光光散射光谱研究了脲和盐酸胍诱导的牛碳酸酐酶B的去折叠.实验结果表明,在脲和盐酸胍诱导的牛碳酸酐酶B的去折叠过程中,溶液中只含有单分子牛碳酸酐酶B和二分子牛碳酸酐酶B集聚体;二分子牛碳酸酐酶B集聚体是通过单分子牛碳酸酐酶B之间的疏水和...     

脲变性牛碳酸酐酶B的稀释复性过程及其集聚作用研究

采用非变性聚丙烯酰胺凝胶电泳、十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、高效凝胶排阻色谱以及激光光散射光谱研究了脲变性牛碳酸酐酶B的稀释复性过程及其集聚作用。在脲变性牛碳酸酐酶B的稀释复性过程中,当最终复性液中脲浓度大于2.0mol/L时,牛碳酸酐酶B在复性液中以单分子和二分子集聚体形式存在;当最终复性液中脲浓度小于2.0mol/L大于1.0mol/L时,牛碳酸酐酶B在复性液中以单分子、二分子集聚体和少量多分子集聚体形式存在;而当最终复性液中脲浓度小于等于1.0mol/L时,脲变性牛碳酸酐酶B复性时会形成均匀透明的上清和不透明的沉淀,牛碳酸酐酶B在上清和沉淀中达到动态解离平衡,且在两相中都以单分子、二分子集聚体和少量多分子集聚体形式存在。溶液中二分子和多分子牛碳酸酐酶B集聚体是通过牛碳酸酐酶B分子之间的疏水和静电相互作用力而形成的,当溶液中这些成分达到一定浓度并且溶液中脲的浓度小于某一个值时,它们之间会通过非共价形式形成沉淀。     

Binding of sulfonamides to erythrocytes and their components

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.     

On origin and evolution of carbonic anhydrase isozymes: A phylogenetic analysis from whole-enzyme to active site

Genetic evolution of carbonic anhydrase enzyme provides an interesting instance of functional similarity in spite of structural diversity of the members of a given family of enzymes. Phylogenetic analysis of α-, β- and γ-carbonic anhydrase was carried out to determine the evolutionary relationships among various members of the family with the enzyme marking its presence in a wide range of cellular and chromosomal locations. The presence of more than one class of enzymes in a particular organism was revealed by phylogenetic time tree. The evolutionary relationships among the members of animal, plant and microbial kingdom were developed. The study revises a long-established notion of kingdom-specificity of the different classes of carbonic anhydrases and provides a new version of the presence of multiple classes of carbonic anhydrases in a single organism and the presence of a given class of carbonic anhydrase across different kingdoms.     

Evaluation of a micro volume pulsed ultrafiltration cell for screening ligands in non-covalent complexes

A pulsed ultrafiltration cell with a 35 microL binding chamber was evaluated for its ability to screen ligands that formed non-covalent complexes with protein targets. The cell was tested with ligands to the targets of carbonic anhydrase and serum albumin. Non-covalent ligand binding to both of these targets was observed and bound ligands were eluted from the cell in less than five min. The cell was also demonstrated to effectively screen a methanolic fermentation broth extract spiked with a known inhibitor to carbonic anhydrase. In addition to detecting specific binding events, the pulsed ultrafiltration method was investigated for its ability to distinguish non-specific binding events. Using carbonic anhydrase with the zinc-binding site removed, it was found that non-specific complexes observed when using electrospray ionization alone were not detected when using the pulsed ultrafiltration mass spectrometry method.     

A caged hydrophobic inhibitor of carbonic anhydrase II

[formula: see text] A tight-binding, hydrophobic inhibitor of carbonic anhydrase II has been masked with a water-solubilizing, photolabile group derived from o-nitrophenylglycine. This caged inhibitor represents our first effort at the site-specific delivery of prodrugs that can be activated by light. Via this approach, we have begun to address the problems of water insolubility and systemic side effects on administration of tight-binding inhibitors of carbonic anhydrase.     

静电纺丝制备中空纤维原位固定化碳酸酐酶用于二氧化碳的吸收

考察了游离碳酸酐酶吸收CO₂水合体系反应条件, 并通过同轴共纺静电纺丝技术制备出中空结构纤维, 实现了碳酸酐酶在中空纤维中的原位包埋, 提高了酶的稳定性并便于回收和重复利用. 实验结果表明, 固定化碳酸酐酶的热稳定性显著增强, 受Cu²⁺和Fe³⁺等金属离子的抑制作用大幅度降低. 连续使用11次后所生成的CaCO₃沉淀量仍能达到首次使用的81.9%. 固定化酶体系生成的CaCO₃沉淀包括方解石型和球文石型2种晶形, 而无酶和加入游离碳酸酐酶的反应体系则主要生成方解石型CaCO₃沉淀.     

A selectivity study of benzenesulfonamide derivatives on human carbonic anhydrase II/IX by 3D-QSAR,Molecular Docking and Molecular Dynamics Simulation

Nowadays, different approaches have been pursued with the intent to develop sulfonamide-like carbonic anhydrase inhibitors that possess better selectivity profiles toward the different human isoforms of the enzyme. Here, we used conventional 3D-QSAR methods, including comparative molecular field analysis (CoMFA), comparative molecular similarity indices analysis (CoMSIA), and Topomer CoMFA, to construct three-dimensional quantitative structure-activity relationship (3D-QSAR) models for benzenesulfonamide derivatives as human carbonic anhydrase (hCA) II/IX inhibitors. The theoretical models had good reliability (R²>0.75) and predictability (Q²>0.55), and the contour maps could graphically present the contributions of the force fields for activity and identify the structural divergence between human carbonic anhydrase II inhibitors and human carbonic anhydrase IX inhibitors. Consequently, we explored the selectivity of inhibitor for human carbonic anhydrase II and IX through molecular docking, and the difference of activity coincides with the potential binding mode well. According to the results of the predicted values and the molecule docking, we found that the inhibitors published in the literature had stronger inhibition on the hCA IX; based on the theoretical models, we designed seven new compounds with good potential activity and reasonably good ADMET profile, which could selectively inhibit hCA IX. Molecular Dynamics Simulation showed that newly-designed compound D7 had good selectivity on hCA IX. The findings from 3D-QSAR and docking studies maybe helpful in the rational drug design of isoform-selective inhibitors.     

Investigating the specific interactions between carbonic anhydrase and a sulfonamide inhibitor by single-molecule force spectroscopy

In this communication, we report on the interaction landscape of an active site-specific enzyme-inhibitor complex by single-molecule force spectroscopy. Electrostatic immobilization was employed to orient a carbonic anhydrase enzyme on a positively charged surface so its active site is pointing upward. This approach to immobilization effectively increases the number of specific interactions measured between the zinc ion of the active site on carbonic anhydrase and a sulfonamide inhibitor tethered to an atomic force microscope (AFM) probe. Further, it reduces the time required for data collection and thereby minimizes the possible mechanical damage to the probe and contamination of the enzyme surface. The rupture force measured at various loading rates is interpreted in terms of a single energy barrier for the carbonic anhydrase enzyme-sulfonamide inhibitor complex from which the kinetic and thermodynamic parameters were estimated on the basis of microscopic models and were compared to the Bell-Evans model. The dissociation rate for the enzyme-inhibitor complex was found to be significantly faster (~35 times) than the natural spontaneous dissociation rate.     

Convergent synthesis of carbonic anhydrase inhibiting bi-heterocyclic benzamides: Structure–activity relationship and mechanistic explorations through enzyme inhibition,kinetics, and computational studies

By using a convergent methodology, a novel series of N-arylated 4-yl-benzamides containing a bi-heterocyclic thiazole–triazole core was synthesized, and the structures of these hybrid molecules, 9a–k , were corroborated through spectral analyses. The in vitro studies of these multifunctional molecules demonstrated their potent carbonic anhydrase inhibition relative to the standard used. The kinetics mechanism was exposed by Lineweaver–Burk plots, which revealed that 9j inhibited carbonic anhydrase non-competitively by forming an enzyme-inhibitor complex. The inhibition constants K_i calculated from Dixon plots for this compound was 1.2 μM. The computational study was also persuasive with the experimental results, and these molecules disclosed good results of all scoring functions and interactions, which suggested a good binding to carbonic anhydrase. So, it was predicted from the inferred results that these molecules might be considered as promising medicinal scaffolds for various diseases related to the uncontrolled production of this enzyme.     

Bicarbonate as a proton donor in catalysis by Zn(II)- and Co(II)-containing carbonic anhydrases.

Catalysis of (18)O exchange between CO(2) and water catalyzed by a Co(II)-substituted mutant of human carbonic anhydrase II is analyzed to show the rate of release of H(2)(18)O from the active site. This rate, measured by mass spectrometry, is dependent on proton transfer to the metal-bound (18)O-labeled hydroxide, and was observed in a site-specific mutant of carbonic anhydrase II in which a prominent proton shuttle residue His64 was replaced by alanine, which does not support proton transport. Upon increasing the concentration of bicarbonate, the rate of release of H(2)(18)O increased in a saturable manner to a maximum of 4 x 10(5) s(-)(1), consistent with proton transfer from bicarbonate to the Co(II)-bound hydroxide. The same mutant of carbonic anhydrase containing Zn(II) had the rate of release of H(2)(18)O smaller by 10-fold, but rate of interconversion of CO(2) and HCO(3)(-) about the same as the Co(II)-containing enzyme. These data as well as solvent hydrogen isotope effects suggest that the bicarbonate transferring the proton is bound to the cobalt in the enzyme. The enhancement of (18)O exchange caused by increasing bicarbonate concentration during catalysis by the Zn(II)-containing carbonic anhydrase from the archaeon Methanosarcina thermophila suggests that a very similar mechanism for proton donation by bicarbonate occurs with this wild-type enzyme.     

Synchrotron Radiation Provides a Plausible Explanation for the Generation of a Free Radical Adduct of Thioxolone in Mutant Carbonic Anhydrase II

Thioxolone acts as a prodrug in the presence of carbonic anhydrase II (CA II), whereby the molecule is cleaved by thioester hydrolysis to the carbonic anhydrase inhibitor, 4-mercaptobenzene-1,3-diol (TH0). Thioxolone was soaked into the proton transfer mutant H64A of CA II in an effort to capture a reaction intermediate via X-ray crystallography. Structure determination of the 1.2 ? resolution data revealed the TH0 had been modified to a 4,4'-disulfanediyldibenzene-1,3-diol, a product of crystallization conditions, and a zinc ligated 2,4-dihydroxybenzenesulfenic acid, most likely induced by radiation damage. Neither ligand was likely a result of an enzymatic mechanism.     

A comparative study of the catalytic mechanisms of the zinc and cadmium containing carbonic anhydrase

The catalytic mechanism for the conversion of carbon dioxide to hydrogen carbonate by a cadmium containing carbonic anhydrase was explored at density functional level employing two different models to simulate the active center of the enzyme. In the first model, the histidine residues around the metal ion were replaced with imidazole groups. Instead, in the second one, the simplest model was extended introducing two amino acidic residues generally present in the neighbor of enzyme and a deep water molecule. The results showed that cadmium carbonic anhydrase follows a reaction mechanism that is favored thermodynamically but not kinetically with respect to that of the most usual zinc-containing enzyme, both in a vacuum and in a protein environment.     

On-column capture of a specific protein in capillary electrophoresis using magnetic beads

A method for capturing specific molecules separated by CE has been explored. To demonstrate on-column capture of migrating analyte molecules, two detection windows were fabricated on a capillary. Magnetic beads containing immobilized molecules that react with the specific molecules under study were placed between the detection windows in the capillary using magnets. Molecules in a sample solution injected into the capillary were separated and detected at the first detection window. After passing through the first detection window, the separated molecules encountered the magnetic beads, where the specific analyte was captured. As a result, the peak area for those analyte molecules decreased or disappeared completely at the second detection window. Rabbit IgG and carbonic anhydrase were employed to demonstrate on-column capture of a specific molecule. For rabbit IgG, magnetic beads containing the immobilized antibody (anti-rabbit IgG) were used. Rabbit IgG molecules were captured on the magnetic beads during CE migration. Furthermore, the capture of carbonic anhydrase was demonstrated by the reaction between magnetic beads (containing immobilized anti-rabbit IgG) and anti-carbonic anhydrase (rabbit IgG), before the beads were packed in the capillary. After packing the magnetic beads in the capillary, a mixture of two proteins was injected into the capillary. Two proteins were detected at the first detection window, while the peak corresponding to carbonic anhydrase disappeared at the second detection window. The results show that using an appropriate antibody, the present technique would be applicable to any proteins.     

Conjugation of poor inhibitors with surface binding groups: a strategy to improve inhibition

Conjugation of surface binding groups with inhibitors for carbonic anhydrase leads to the conversion of weak inhibitors to strong inhibitors.     

A versatile polypeptide platform for integrated recognition and reporting: affinity arrays for protein-ligand interaction analysis

A molecular platform for protein detection and quantification is reported in which recognition has been integrated with direct monitoring of target-protein binding. The platform is based on a versatile 42-residue helix-loop-helix polypeptide that dimerizes to form four-helix bundles and allows site-selective modification with recognition and reporter elements on the side chains of individually addressable lysine residues. The well-characterized interaction between the model target-protein carbonic anhydrase and its inhibitor benzenesulfonamide was used for a proof-of-concept demonstration. An affinity array was designed where benzenesulfonamide derivatives with aliphatic or oligoglycine spacers and a fluorescent dansyl reporter group were introduced into the scaffold. The affinities of the array members for human carbonic anhydrase II (HCAII) were determined by titration with the target protein and were found to be highly affected by the properties of the spacers (dissociation constant Kd=0.02-3 microM). The affinity of HCAII for acetazolamide (Kd=4 nM) was determined in a competition experiment with one of the benzenesulfonamide array members to address the possibility of screening substance libraries for new target-protein binders. Also, successful affinity discrimination between different carbonic anhydrase isozymes highlighted the possibility of performing future isoform-expression profiling. Our platform is predicted to become a flexible tool for a variety of biosensor and protein-microarray applications within biochemistry, diagnostics and pharmaceutical chemistry.     

High-resolution ion isolation with the ion cyclotron resonance capacitively coupled open cell

For ion cyclotron resonance, a capacitively coupled open cell variant with fourfold radial symmetry was constructed and tested for axial excitation-ejection of large ions at high resolution. With a reverse of frequency sweep direction, this cell gave substantial improvements in signal-to-noise ratio due to linearization of the excitation electric field. Single isotopic peaks of ubiquitin (8.6-kDa) and carbonic anhydrase (29-kDa) molecular ions could be isolated by selective stored waveform inverse Fourier transform excitation, which yielded an order of magnitude higher isolation resolving power than previously achieved at high mass-to-charge ratio values.     

The binding of human carbonic anhydrase II by functionalized folded polypeptide receptors

Several receptors for human carbonic anhydrase II (HCAII) have been prepared by covalently attaching benzenesulfonamide carboxylates via aliphatic aminocarboxylic acid spacers of variable length to the side chain of a lysine residue in a designed 42 residue helix-loop-helix motif. The sulfonamide group binds to the active site zinc ion of human carbonic anhydrase II located in a 15 A deep cleft. The dissociation constants of the receptor-HCAII complexes were found to be in the range from low micromolar to better than 20 nM, with the lowest affinities found for spacers with less than five methylene groups and the highest affinity found for the spacer with seven methylene groups. The results suggest that the binding is a cooperative event in which both the sulfonamide residue and the helix-loop-helix motif contribute to the overall affinity.     

Recognition of isozymes via lanthanide ion incorporated polymerized liposomes

We report the selective recognition of carbonic anhydrase isozymes based on the excited-state lifetimes of chelated Eu(3+) ions incorporated in polymerized liposomes.     

碳酸酐酶及其模型研究进展*

本文综述了近年来碳酸酐酶及其化学模型两方面的最新研究进展,对其中的问题和进一步的研究进行了简要的讨论。