Biomedical subjects

Xun Fu

Publications and source records attributed to Xun Fu.

12 recordsLinked to original sources

PubMed2006

The in vitro characterization of the iterative avermectin glycosyltransferase AveBI reveals reaction reversibility and sugar nucleotide flexibility.

The glycosyltransferase AveBI, which is involved in the biosynthesis of the macrolide antihelmintic avermectin (AVM), was characterized in vitro. AveBI was confirmed to catalyze two separate iterative additions of l-oleandrose, and the reversibility of AveBI-catalyzed reaction was also demonstrated. Investigation of sugar nucleotide specificity revealed 10 unique sugar nucleotide substrates which, in combination with five distinct aglycones, led to the production of 50 differentially glycosylated AVM variants.

Catalysis↗

PubMed2006

Exploiting the reversibility of natural product glycosyltransferase-catalyzed reactions.

Glycosyltransferases (GTs), an essential class of ubiquitous enzymes, are generally perceived as unidirectional catalysts. In contrast, we report that four glycosyltransferases from two distinct natural product biosynthetic pathways-calicheamicin and vancomycin-readily catalyze reversible reactions, allowing sugars and aglycons to be exchanged with ease. As proof of the broader applicability of these new reactions, more than 70 differentially glycosylated calicheamicin and vancomycin variants are reported. This study suggests the reversibility of GT-catalyzed reactions may be general and useful for generating exotic nucleotide sugars, establishing in vitro GT activity in complex systems, and enhancing natural product diversity.

Aminoglycosides↗

PubMed2006

RebG- and RebM-catalyzed indolocarbazole diversification.

Rebeccamycin and staurosporine represent two broad classes of indolocarbazole glycoside natural products with antitumor properties. Based upon previous sequence annotation and in vivo studies, rebG encodes for the rebeccamycin N-glucosyltransferase, and rebM for the requisite 4'-O-methyltransferase. In the current study, an efficient in vivo biotransformation system for RebG was established in both Streptomyces lividans and Escherichia coli. Bioconversion experiments revealed RebG to glucosylate a set of indolocarbazole surrogates, the products of which could be further modified by in vitro RebM-catalyzed 4'-O-methylation. Both RebG and RebM displayed substrate promiscuity, and evidence for a remarkable lack of RebG regioselectivity in the presence of asymmetric substrates is also provided. In the context of the created indolocarbazole analogues, cytotoxicity assays also highlight the importance of 4'-O-methylation for their biological activity.

Bacterial Proteins↗

PubMed2005

Solvothermal synthesis of hollow ZnS spheres.

Mono-dispersed semiconductor ZnS hollow spheres with the diameter of 300-500 nm and the shell thickness of about 100-150 nm have been synthesized successfully by solvothermal method from ethanol solution in the presence of a special surfactant-quaternary ammonium salt of 2-undecyl-1-dithioureido-ethyl-imidazoline (SUDEI) made in our lab. The mono-dispersed ZnS hollow spheres are characterized by XRD, size distribution investment, UV-vis, TEM, and SEM, respectively. The UV-vis measurement indicates that there is a broad absorption at 210-280 nm, which is likely to be caused by "hollow-effect." A growth mechanism of ZnS hollow spheres has also been put forward and discussed.

Journal Article↗

PubMed2005

Diversifying vancomycin via chemoenzymatic strategies.

[reaction: see text] The rapid diversification of glycopeptides via glycorandomization reveals that significantly diverse substitutions are tolerated and suggests there may be a synergistic benefit to the construction of mechanistically related natural product core scaffold fusions. This work also further highlights the utility of chemoenzymatic approaches to diversify complex natural product architectures.

Combinatorial Chemistry Techniques↗

PubMed2005

Fabrication of hollow spheres and thin films of nickel hydroxide and nickel oxide with hierarchical structures.

Hollow spheres and thin films of Ni(OH)(2) and NiO with unusual form and hierarchical structures have been synthesized by a simple solution chemistry method. First, in situ formed Ni(OH)(2) nanoflakelets organized on the surface of styrene-acrylic acid copolymer (PSA) latex particles to form core/shell structures. Ni(OH)(2) hollow shells built up with nanoflakelets were obtained after subsequent removal of the core latex particles by dissolving PSA latex in toluene; the removal of the cores by calcinations would result in NiO hollow shells, also with hierarchical structures. BET calculation showed the surface area of the NiO hollow spheres was 156 m(2)/g. The nanoflakelets could also organize themselves into thin films with hierarchical structures. It is anticipated that these novel structures will have some unique applications in Ni-based batteries and other potentials.

Journal Article↗

PubMed2005

Structure-based engineering of E. coli galactokinase as a first step toward in vivo glycorandomization.

In vitro glycorandomization is a rapid chemoenzymatic strategy to diversify complex natural product scaffolds. The glycorandomization sugar activation pathway is dependent upon the efficient construction of diverse sugar-1-phosphate libraries. In the context of the previously evolved GalK Y371H "gatekeeper" mutation, the active site M173L mutation described herein presents a kinase with remarkably broadened substrate range to include 28 diverse natural and unnatural sugars. Among these new substrates, 6-azido-6-deoxy-galactose and 6-azido-6-deoxy-glucose present unique chemical probes to assess the utility of an E. coli Y371H/M173L-GalK-overproducing strain to generate unnatural sugar-1-phosphates in vivo. Remarkably, the in vivo conversion of both unnatural sugars rival that demonstrated in vitro. This notable in vivo success stands as the first step toward constructing short sugar-activation pathways in vivo and, ultimately, in vivo natural-product glycorandomization.

Binding Sites↗

PubMed2004

Preparation and characterization of silver/TiO2 composite hollow spheres.

Silver-coated poly(methyl acrylic acid) (PSA) core-shell colloid particles were prepared by an in situ chemical reduction method. Crystalline silver/titania composite hollow spheres were obtained by coating the as-prepared PSA/silver particles with an amorphous titania layer and subsequently calcining in Ar atmosphere. SEM and TEM investigation indicated that the size of the as-prepared PSA/silver and PSA/silver/TiO(2) core-shell particles and silver/titania composite hollow particles was fairly uniform and the wall thickness of the hollow spheres was in the range of 40-80 nm. UV-vis absorption spectra were recorded to investigate their optical properties.

Colloids↗

PubMed2004

Natural product glycorandomization.

glycorandomization is a chemoenzymatic strategy that overcomes the limitations in natural product derivatization associated with both solely chemistry-based approaches or in vivo engineering. In this article we present the basic strategies for glycorandomization development as a next-generation tool in drug discovery.

Carbohydrate Sequence↗

PubMed2003

Antibiotic optimization via in vitro glycorandomization.

In nature, the attachment of sugars to small molecules is often used to mediate targeting, mechanism of action and/or pharmacology. As an alternative to pathway engineering or total synthesis, we report a useful method, in vitro glycorandomization (IVG), to diversify the glycosylation patterns of complex natural products. We have used flexible glycosyltransferases on nucleotide diphosphosugar (NDP-sugar) libraries to generate glycorandomized natural products and then applied chemoselective ligation to produce monoglycosylated vancomycins that rival vancomycin.

Anti-Bacterial Agents↗

PubMed2003

Preparation of mesoporous ZrO2 with the middle phase formed in a trioctyl (or alkyl) phosphinic oxide-kerosene/HCl-ZrOCl2 extraction system.

The extraction behavior and phase behavior of TOPO (or TRPO)-kerosene/HCl-ZrOCl(2) systems have been investigated. The middle phase with bicontinuous structure is first used as both the Zr(IV) source and the template to prepare mesoporous material just by precipitation with aqua ammonia under low temperature. By this method, crystal mesoporous ZrO(2) powders with average d-values of 6.3 and 7.48 nm, respectively, have been obtained. TG-DTA, TEM, and XRD are adopted for the characterization of the synthesized sample.

Journal Article↗

PubMed2003

Studies on the substrate specificity of Escherichia coli galactokinase.

In vitro glycorandomization (IVG) technology is dependent upon the ability to rapidly synthesize sugar phosphates. Compared with chemical synthesis, enzymatic (kinase) routes to sugar phosphates would be attractive for this application. This work focuses upon the development of a high-throughput colorimetric galactokinase (GalK) assay and its application toward probing the substrate specificity and kinetic parameters of Escherichia coli GalK. The demonstrated dinitrosalicylic assay should also be generally applicable to a variety of sugar-processing enzymes. [reaction: see text]

Colorimetry↗