系列微孔磷酸镓的合成与结构研究

目前,新型微孔无机固体化合物的合成是一个活跃的研究领域,本文报道在R-Ga₂O₃-P₂O₅-H₂O体系中(R=有机模板剂)系列磷酸镓分子筛的合成与结构的研究。     

一类六核三价铁簇化合物的合成及结构表征

选择3种不同尺寸含氮配体（哌嗪、咪唑和三氮唑）与三羟甲基丙烷（H₃tmp）和FeCl₃采用溶剂热反应合成3例六核Fe（Ⅲ）合物：（C₅H₁₄N₂）[Fe₆（μ₆-O）Cl₆（tmp）₄]·2H₂O·CH₃OH （1）、（C₃H₅N₂）₂[Fe₆（μ₆-O）Cl₆（tmp）₄] （2）和（C₄H₈N₃）₃（C₂H₄N₃）[Fe12（μ₆-O）₂Cl₁₂（tmp）₈]·3CH₃OH （3）,并对它们的结构进行表征。发现三元醇配体有利于合成高核金属簇。3个化合物具有相同的阴离子簇[Fe₆（μ₆-O）Cl₆（tmp）₄]^2-。通过晶体学参数,元素分析,红外等手段证实,在化合物1和3的体系中,氮杂环配体经历了N-和C-烷基化反应。     

X-Ray Crystallography as a Tool to Determine Three-Dimensional Structures of Commercial Enzymes Subjected to Treatment in Pressurized Fluids

The study of enzyme function often involves a multi-disciplinary approach. Several techniques are documented in the literature towards determining secondary and tertiary structures of enzymes, and X-ray crystallography is the most explored technique for obtaining three-dimensional structures of proteins. Knowledge of three-dimensional structures is essential to understand reaction mechanisms at the atomic level. Additionally, structures can be used to modulate or improve functional activity of enzymes by the production of small molecules that act as substrates/cofactors or by engineering selected mutants with enhanced biological activity. This paper presentes a short overview on how to streamline sample preparation for crystallographic studies of treated enzymes. We additionally revise recent developments on the effects of pressurized fluid treatment on activity and stability of commercial enzymes. Future directions and perspectives on the the role of crystallography as a tool to access the molecular mechanisms underlying enzymatic activity modulation upon treatment in pressurized fluids are also addressed.     

An Approach for Visualization of the Active Site of Enzymes with Unknown Three-Dimensional Structures

Abstract

A new approach for virtual characterization of the active site structure of enzymes with unknown three-dimensional (3D) structure has been proposed. It includes analysis of data on enzyme interaction with reversible competitive inhibitors, their 3D structures and moulding of the substrate-binding region. The superposition of ligands in biologically active conformations allows to determine the shape and dimension of the active site cavity accommodating these compounds. Monoamine oxidase A (MAO-A), a “typical” enzyme with unknown spatial organisation, was used to test this method. The correctness of such approach was validated by the analysis of HIV protease interaction with its inhibitors using 3D structures of their complexes. Mould of the substrate/inhibitor binding site can be used for the visualization of this binding site and for searching new ligands in molecular databases.     

Identification of the Enzymes Mediating the Maturation of the Seryl-tRNA Synthetase Inhibitor SB-217452 during the Biosynthesis of Albomycins

Albomycin δ₂ is a sulfur-containing sideromycin natural product that shows potent antibacterial activity against clinically important pathogens. The l -serine-thioheptose dipeptide partial structure, known as SB-217452, has been found to be the active seryl-tRNA synthetase inhibitor component of albomycin δ₂. Herein, it is demonstrated that AbmF catalyzes condensation between the 6′-amino-4′-thionucleoside with the d -ribo configuration and seryl-adenylate supplied by the serine adenylation activity of AbmK. Formation of the dipeptide is followed by C3′-epimerization to produce SB-217452 with the d -xylo configuration, which is catalyzed by the radical S-adenosyl-l -methionine enzyme AbmJ. Gene deletion suggests that AbmC is involved in peptide assembly linking SB-217452 with the siderophore moiety. This study establishes how the albomycin biosynthetic machinery generates its antimicrobial component SB-217452.     

Computer Simulation of Porous Electrodes with Immobilized Enzymes: The Percolation Properties of Multicomponent Structures

The percolation characteristics of porous electrodes with immobilized enzymes are calculated. It is presumed that active centers of the enzymes undergo direct oxidation or reduction on the electrode. Two versions of a three-dimensional electrode structure consisting of particles of identical size are studied. In one, the frame of the porous electrode (PE) comprises only those parts of the support that conduct electrons. In the other, the electrode is a two-component structure capable of ensuring the supply of two participants of the electrochemical process to the enzymes. Calculated are: the fraction of the support parts that conduct electrons (taken as a whole, they form an electron cluster); the electron cluster's transparency; and the number of exits the electron cluster has onto the rear surface of PE. The character of distribution of enzymes that are in contact with one or two macroscopic clusters, which comprise conductive particles, over the PE thickness is established. In doing so, it is assumed that the two clusters can be supplied either from one side (parallel clusters) or from two opposite sides (collision clusters) of PE. The electron cluster surface accessible to contact with enzymes and the number of enzymes in contact with such an electron cluster are determined. Two possibilities of the PE functioning are examined. In one, the electrochemical process proceeds at any contact of the enzyme with the support particles. In the other, a certain type of enzyme immobilization on the support is required. The region of optimum concentrations of components that make PE is established. Within this region the electrochemical activity may reach a maximum.     

Crystal Structures of a Family of New Copper(I) Cyanide Complexes of Thiourea and Substituted Thioureas

The syntheses and crystal structures of the first cyanide, sulfur mixed ligand copper(I) complexes are reported. The first complex of the family was discovered when (CuCN)(3)(C(6)H(12)N(4))(2) (1) (C(6)H(12)N(4) = hexamethylenetetramine) was treated with aqueous thiourea. The sulfur ligands include thiourea (tu), 1,3-dimethyl-2-thiourea (dmtu), 1,3-diethyl-2-thiourea (detu), 1,1,3,3-tetramethyl-2-thiourea (tmtu), and 2-imidazolidinethione (N,N'-ethylenethiourea, etu). Synthesis was effected by adding the ligand to a solution of CuCN in aqueous sodium thiosulfate. Complex 2, (CuCN)(2)(tu)(3)(H(2)O), crystallizes in the triclinic space group P&onemacr;with unit cell dimensions a = 7.696(5) ?, b = 9.346(2) ?, c = 10.772(2) ?, alpha = 106.53(2) degrees, beta = 91.11(4) degrees, gamma = 98.42(3) degrees, and Z = 2. Complex 3, (CuCN)(3)(dmtu)(2), crystallizes in the monoclinic space group Cc with unit cell dimensions a = 10.082(3) ?, b = 14.984(5) ?, c = 11.413(3) ?, beta = 104.50(2) degrees, and Z = 4. Complex 4, (CuCN)(2)(detu)(H(2)O), crystallizes in the monoclinic space group P2(1)/n with unit cell dimensions a = 7.969(5) ?, b = 11.559(4) ?, c = 13.736(5) ?, beta = 100.48(4) degrees, and Z = 4. Complex 5, (CuCN)(tmtu) (polymorph a), crystallizes in the orthorhombic space group P2(1)2(1)2(1) with unit cell dimensions a = 8.653(1) ?, b = 9.426(1) ?, c = 11.620(3) ?, and Z = 4. Complex 6, (CuCN)(tmtu) (polymorph b), which has the same connectivity as 5, crystallizes in the triclinic space group P&onemacr; with unit cell dimensions a = 9.660(4) ?, b = 14.202(4) ?, c = 16.03(1) ?, alpha = 101.68(5) degrees, beta = 107.08(6) degrees, gamma = 70.07(2) degrees, and Z = 8. The difference between the polymorphs is that 5 has a zig-zag chain with a repeat unit of two while 6 has a 4-fold helix. Complex 7, (CuCN)(2)(etu), crystallizes in the monoclinic space group P2(1)( )()with unit cell dimensions a = 3.994(2) ?, b = 13.886(3) ?, c = 7.556(1) ?, beta = 97.07(2) degrees, and Z = 2.     

Intracellular Detection and Evolution of Site-Specific Proteases Using a Genetic Selection System

Development of endoproteases, programmed to promote degradation of peptides or proteins responsible for pathogenic states, represents an attractive therapeutic strategy, since such biocatalytic agents could be directed against a potentially unlimited repertoire of extracellular proteinaceous targets. Difficulties associated with engineering enzymes with tailor-made substrate specificities have, however, hindered the discovery of proteases possessing both the efficiency and selectivity to act as therapeutics. Here, we disclose a genetic system, designed to report on site-specific proteolysis through the survival of a bacterial host, and the implementation of this method in the directed evolution of proteases with a non-native substrate preference. The high sensitivity potential of this system was established by monitoring the activity of the Tobacco Etch Virus protease (TEV-Pr) against co-expressed substrates of various recognition level and corroborated by both intracellular and cell-free assays. The genetic selection system was then used in an iterative mode with a library of TEV-Pr mutants to direct the emergence of proteases favoring a nominally poor substrate of the stringently selective protease. The retrieval of mutant enzymes displaying enhanced proteolytic properties against the non-native sequence combined with reduced recognition of the cognate hexapeptide substrate demonstrates the potential of this system for evolving proteases with improved or completely unprecedented properties.     

The Crystal Structure of RosB: Insights into the Reaction Mechanism of the First Member of a Family of Flavodoxin‐like Enzymes

8‐demethyl‐8‐aminoriboflavin‐5′‐phosphate (AFP) synthase (RosB) catalyzes the key reaction of roseoflavin biosynthesis by forming AFP from riboflavin‐5′‐phosphate (RP) and glutamate via the intermediates 8‐demethyl‐8‐formylriboflavin‐5′‐phosphate (OHC‐RP) and 8‐demethyl‐8‐carboxylriboflavin‐5′‐phosphate (HO₂C‐RP). To understand this reaction in which a methyl substituent of an aromatic ring is replaced by an amine we structurally characterized RosB in complex with OHC‐RP (2.0 Å) and AFP (1.7 Å). RosB is composed of four flavodoxin‐like subunits which have been upgraded with specific extensions and a unique C‐terminal arm. It appears that RosB has evolved from an electron‐ or hydride‐transferring flavoprotein to a sophisticated multi‐step enzyme which uses RP as a substrate (and not as a cofactor). Structure‐based active site analysis was complemented by mutational and isotope‐based mass‐spectrometric data to propose an enzymatic mechanism on an atomic basis.     

Identification of the Enzymes Mediating the Maturation of the Seryl‐tRNA Synthetase Inhibitor SB‐217452 during the Biosynthesis of Albomycins

Albomycin δ₂ is a sulfur‐containing sideromycin natural product that shows potent antibacterial activity against clinically important pathogens. The l ‐serine‐thioheptose dipeptide partial structure, known as SB‐217452, has been found to be the active seryl‐tRNA synthetase inhibitor component of albomycin δ₂. Herein, it is demonstrated that AbmF catalyzes condensation between the 6′‐amino‐4′‐thionucleoside with the d ‐ribo configuration and seryl‐adenylate supplied by the serine adenylation activity of AbmK. Formation of the dipeptide is followed by C3′‐epimerization to produce SB‐217452 with the d ‐xylo configuration, which is catalyzed by the radical S‐adenosyl‐l ‐methionine enzyme AbmJ. Gene deletion suggests that AbmC is involved in peptide assembly linking SB‐217452 with the siderophore moiety. This study establishes how the albomycin biosynthetic machinery generates its antimicrobial component SB‐217452.