Biosynthesis of lovastatin analogs with a broadly specific acyltransferase

The natural product lovastatin and its semisynthetic, more effective derivative, simvastatin, are important drugs for the treatment of hypercholesterolemia. Here, we report the biochemical characterization of a dedicated acyltransferase, LovD, encoded in the lovastatin biosynthetic pathway. We demonstrate that LovD has broad substrate specificity towards the acyl carrier, the acyl substrate, and the decalin acyl acceptor. LovD can efficiently catalyze the acyl transfer from coenzyme A thioesters or N-acetylcysteamine (SNAC) thioesters to monacolin J. When alpha-dimethylbutyryl-SNAC was used as the acyl donor, LovD was able to convert monacolin J and 6-hydroxyl-6-desmethylmonacolin J into simvastatin and huvastatin, respectively. Using the Escherichia coli LovD overexpression strain as a whole-cell biocatalyst, preparative amounts of simvastatin were synthesized in a single fermentation step. Our results demonstrate LovD is an attractive enzyme for engineered biosynthesis of pharmaceutically important cholesterol-lowering drugs.     

Characterization of a specific arabinosyltransferase activity involved in mycobacterial arabinan biosynthesis

Mycobacterium smegmatis strains that contain inactivated EmbA or EmbB proteins are unable to synthesize terminal Arabeta1-->2Araalpha1-->5(Arabeta1-->2Araalpha1-->3)Araalpha1-->5Araalpha1-->(Ara(6)) motif in the cell wall polysaccharide arabinogalactan. Instead, the mutants contain a linear Arabeta1-->2Araalpha1-->5Araalpha1-->5Araalpha1-->(Ara(4)) motif, suggesting that these proteins are involved in the synthesis or transfer of the disaccharide Arabeta1-->2Araalpha1--> to an internal 5-linked Ara. Therefore, we synthesized a linear Arabeta1-->2Araalpha1-->5Araalpha1-->5Araalpha1-->5Araalpha1--> with an octyl aglycon as an arabinosyl acceptor in cell-free assays. A facile assay was developed using the chemically synthesized glycan, membrane, and particulate cell wall as the enzyme source, and 5-phosphoribose diphosphate pR[(14)C]pp as the arabinose donor. The results unequivocally show that two arabinofuranosyl residues were added at the tertiary -->5Araalpha1--> of the synthetic glycan. This activity was undetectable in strains of M. smegmatis where embB or embA had been genetically disrupted. Normal activity could be restored only in the presence of both EmbA and EmbB proteins.     

Beyond ethylmalonyl-CoA: the functional role of crotonyl-CoA carboxylase/reductase homologs in expanding polyketide diversity

This review covers the emerging biosynthetic role of crotonyl-CoA carboxylase/reductase (CCR) homologs in extending the structural and functional diversity of polyketide natural products. CCRs catalyze the reductive carboxylation of α,β-unsaturated acyl-CoA substrates to produce a variety of substituted malonyl-CoA derivatives employed as polyketide synthase extender units. Here we discuss the history of CCRs in both primary and secondary metabolism, the mechanism by which they function, examples of new polyketide diversity from pathway specific CCRs, and the role of CCRs in facilitating the bioengineering novel polyketides.     

Expression of monolysocardiolipin acyltransferase activity is regulated in concert with the level of cardiolipin and cardiolipin biosynthesis in the mammalian heart

Background  

Monolysocardiolipin acyltransferase (MLCL AT) catalyzes the acylation of monolysocardiolipin to cardiolipin in mammalian tissues. We previously reported that cardiac cardiolipin levels, MLCL AT and cardiolipin synthase activities were all elevated in rats made hyperthyroid by thyroxine treatment. In this study, we examined if cardiac mitochondrial MLCL AT activity was dependent upon the biosynthesis and level of cardiolipin in the heart. Rat heart mitochondrial MLCL AT activity was determined under conditions in which the levels of cardiac cardiolipin and cardiolipin synthase activity were either reduced or unaltered using four different disease models in the rat. In addition, these parameters were examined in a murine model of cardiac cell differentiation.     

Room-Temperature Ionic Liquids: For a Difference in the Supramolecular Synthesis

Cu(I) and Ni(II) coordination polymers with 4,4′-bipyridine and 2,2′-bipyridine, respectively, that have been synthesized from an ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate) gave different coordination environment and supramolecular networks than the corresponding synthesis from the other solvents. The resultant complexes were characterized by single crystal x-ray diffraction methods.     

Supramolecular interactions in a family of dinuclear helicates in the solid-state

ABSTRACT

Metallo-helicates are a commonly encountered assembly within supramolecular chemistry. Interest in these architectures stems from their inherent helical chirality which positions them for a diverse range of applications such as catalysis and non-linear optics (NLO). The current study uses Co(II) dinuclear double helicates as versatile supramolecular synthons. The ditopic ligand, L, features two tridentate quinolinyl-hydrazone binding sites imparting it with hydrogen bond donors and π-faces for secondary supramolecular interactions. Incorporation of L into [Co₂(L)₂]⁴⁺ helical assemblies results in a helical cationic supramolecular synthon with moieties predisposed to forming π-π stacking and hydrogen bond interactions. The single-crystal X-ray structures of [Co₂(L)₂]X₄ (X = ClO₄ ^?, BF₄ ^? and CF₃SO₃ ^?) revealed a variety of anion dependent hydrogen bond networks arising through the interaction of the hydrazide hydrogen with the anion. These interactions in turn strongly influence the nature of the π-π stacking interactions of the quinoline moieties which can be analysed via the Hirshfield surface.     

Supramolecular effects on the dynamics of radicals in MFI zeolites: a direct EPR investigation

Photolysis of the supramolecular complexes (dibenzyl ketones@ZSM-5) produced supramolecular complexes of benzyl radicals@ZSM-5, which were directly detected by CW-EPR spectroscopy, and provided information on the dynamics of the radicals. The lifetimes of the radicals increased as the group X attached to the carbon atom at the radical center increases from X = H (t(1/2) ca. 2 min) to X = (CH(2))(4)CH(3) (t(1/2) > 200 min). In addition, line broadening of the EPR signal was observed as the group X increases. Experiments involving cation-exchanged zeolites (MZSM-5; M = Li, Na, K, Rb, Cs) showed a strong dependence of the radical lifetime on the size of the cation (t(1/2) ca. 10 min for Li and t(1/2) > 200 min for Cs). The results are discussed in terms of supramolecular steric effects on the radical-radical reactions in the zeolite supercages.     

Supramolecular organization in the solid state of a novel soluble polydiacetylene

The synthesis of the monomer 1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne, its polymerization and the purification of the polymer, which is soluble in common organic solvents, are reported. Results from powder X-ray diffraction studies carried out on the red form of the polymer are discussed. The red polymer chains self-assemble into cylindrical shapes which produce hexagonal columnar mesophases with a transition from a more (Colho) to a less ordered (Colhd) structure around 85 C. The role played by the long alkyl chains in the formation of the supramolecular hexagonal mesophase is emphasized by comparing these results with those obtained from an analogous polymer with dodecyl substituents which exhibits only the Colhd structure over the whole range of temperature explored.     

Symbiotic cooperation in the biosynthesis of a phytotoxin

Division of labor: A combination of genetic, microbial, and chemical analyses solved the riddle of the dual epoxidation in the biosynthesis of rhizoxin, the causative agent of rice seedling blight. Bacterial endosymbionts of Rhizopus microsporus mediate the first epoxidation by a dedicated cytochrome P450 monooxygenase. The second oxirane ring is introduced by the fungal host and results in a substantially increased potency of the phytotoxin.     

Electron Transfer in a Supramolecular Associate of a Fullerene Fragment

Herein, we investigate the association of a fullerene fragment, hemifullerene C₃₀H₁₂, with an electron‐donating bowl‐shaped tetrathiafulvalene derivative (truxTTF). UV/Vis titrations and DFT calculations support formation of the supramolecular complex, for which an association constant of log K_a=3.6±0.3 in CHCl₃ at room temperature is calculated. Remarkably, electron transfer from truxTTF to C₃₀H₁₂ to form the fully charge‐separated species takes place upon irradiation of the associate with light, constituting the first example in which a fullerene fragment mimics the electron‐accepting behavior of fullerenes within a supramolecular complex.     

Supramolecular control in carbohydrate epimerization: discovery of a new anion host-guest system

A new anion-carbohydrate recognition system is described. Pyranosides with axial protons in 1-, 3-, and 5-position proved efficient, forming relatively strong complexes between the anion and the B-face of the carbohydrate. This system could furthermore be used in supramolecular control in Lattrell-Dax epimerization reactions, leading to either activation or deactivation effects.     

青蒿素生物合成的研究III: 青蒿素和青蒿素B生物合成中的关键性中间体-青蒿素

以[15-^3H]青蒿酸为前体用青蒿匀聚浆体进行青蒿素和青蒿素B的生物合成.实验结果表明, 在青蒿植物由MVA生物合成青蒿素和青蒿素B的途径中, 青蒿酸是关键性中间体.     

Hierarchical Supramolecular Spinning of Nanofibers in a Microfluidic Channel: Tuning Nanostructures at a Dynamic Interface

One of the fundamental problems in supramolecular chemistry, as well as in material sciences, is how to control the self‐assembly of polymers on the nanometer scale and how to spontaneously organize them towards the macroscopic scale. To overcome this problem, inspired by the self‐assembly systems in nature, which feature the dynamically controlled self‐assembly of biopolymers, we have previously proposed a self‐assembly system that uses a dynamic liquid/liquid interface with dimensions in the micrometer regime, thereby allowing polymers to self‐assemble under precisely controlled nonequilibrium conditions. Herein, we further extend this system to the creation of hierarchical self‐assembled architectures of polysaccharides. A natural polysaccharide, β‐1,3‐glucan (SPG), and water were injected into opposite “legs” of microfluidic devices that had a Y‐shape junction, so that two solvents would gradually mix in the down stem, thereby causing SPG to spontaneously self‐assemble along the flow in a head‐to‐tail fashion, mainly through hydrophobic interactions. In the initial stage, several SPG nanofibers would self‐assemble at the Y‐junction owing to the shearing force, thereby creating oligomers with a three‐way junction point. This unique structure, which could not be created through conventional mixing procedures, has a divergent self‐assembly capability. The dynamic flow allows the oligomers to interact continuously with SPG nanofibers that are fed into the Y‐junction, thus amplifying the nanostructure along the flow to form SPG networks. Consequently, we were able to create stable, centimeter‐length macroscopic polysaccharide strands under the selected flow conditions, which implies that SPG nanofibers were assembled hierarchically in a supramolecular fashion in the dynamic flow. Microscopic observations, including SEM and AFM analysis, revealed the existence of clear hierarchical structures inside the obtained strand. The network structures self‐assembled to form sub‐micrometer‐sized fibers. The long fibers further entangled with each other to give stable micrometer‐sized fibers, which finally assembled to form the macroscopic strands, in which the final stabilities in the macroscopic regime were governed by that of the network structures in the nanometer regime. Thus, we have exploited this new supramolecular system to create hierarchical polymeric architectures under precisely controlled flow conditions, by combining the conventional supramolecular strategy with microfluidic science.