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Changsheng Zhang

Publications and source records attributed to Changsheng Zhang.

9 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

Structural insight into the self-sacrifice mechanism of enediyne resistance.

The recent discovery of the first "self-sacrifice" mechanism for bacterial resistance to the enediyne antitumor antibiotics, where enediyne-induced proteolysis of the resistance protein CalC inactivates both the highly reactive metabolite and the resistance protein, revealed yet another ingenious bacterial mechanism for controlling reactive metabolites. As reported herein, the first 3D structures of CalC and CalC in complex with calicheamicin (CLM) divulge CalC to be a member of the steroidogenic acute regulatory protein (StAR)-related transfer (START) domain superfamily. In contrast to previous studies of proteins known to bind DNA-damaging natural products ( e.g ., bleomycins, mitomycins, and nine-membered chromoprotein enediynes), this is the first demonstrated involvement of a START domain fold. Consistent with the CalC self-sacrifice mechanism, CLM in complex with CalC is positioned for direct hydrogen abstraction from Gly113 to initiate the oxidative proteolysis-based resistance mechanism. These structural studies also illuminate, for the first time, a small DNA-binding region within CalC that may serve to localize CalC to the enediyne target (DNA). Given the role of START domains in nuclear/cytosolic transport and translocation, this structural study also may implicate START domains as post-endocytotic intracellular chaperones for enediyne-based therapeutics such as MyloTarg.

Aminoglycosides↗
PubMed2006

Natural product diversification using a non-natural cofactor analogue of S-adenosyl-L-methionine.

Adenosine analogues bearing either 5'-aziridine or 5'-N-mustard electrophiles are methyltransferase-dependent DNA alkylating agents. We present here a novel synthetic cofactor bearing a pendant 5'-amino acid N-mustard. Unlike previously studied synthetic cofactors, this material is very efficiently used by the natural product biosynthetic enzyme rebeccamycin methyltransferase (RebM) to generate a number of new rebeccamycin analogues. These data promote the notion that natural product methyltransferases can be used with non-natural cofactors to enhance the molecular diversity of natural product analogues for drug discovery. To our knowledge, this is the first documentation of a biological methyltransferase, other than DNA methyltransferases, that can exploit such synthetic cofactors.

Alkylation↗
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↗
PubMed2006

Deciphering indolocarbazole and enediyne aminodideoxypentose biosynthesis through comparative genomics: insights from the AT2433 biosynthetic locus.

AT2433, an indolocarbazole antitumor antibiotic, is structurally distinguished by its aminodideoxypentose-containing disaccharide and asymmetrically halogenated N-methylated aglycon. Cloning and sequence analysis of AT2433 gene cluster and comparison of this locus with that encoding for rebeccamycin and the gene cluster encoding calicheamicin present an opportunity to study the aminodideoxypentose biosynthesis via comparative genomics. The locus was confirmed via in vitro biochemical characterization of two methyltransferases--one common to AT2433 and rebeccamycin, the other unique to AT2433--as well as via heterologous expression and in vivo bioconversion experiments using the AT2433 N-glycosyltransferase. Preliminary studies of substrate tolerance for these three enzymes reveal the potential to expand upon the enzymatic diversification of indolocarbazoles. Moreover, this work sets the stage for future studies regarding the origins of the indolocarbazole maleimide nitrogen and indolocarbazole asymmetry.

Amino Sugars↗
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↗
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↗