Crystallization and preliminary X-ray analysis of the aromatic prenyltransferase CloQ from the clorobiocin biosynthetic cluster of Streptomyces roseochromogenes

Screening the NCI diversity set V for anti-MRSA activity: cefoxitin synergy and LC-MS/MS confirmation of folate/thymidine biosynthesis inhibition

IMPORTANCE

New antibacterial agents are urgently needed to counter increasingly resistant bacteria. One approach to this problem is library screening for new antibacterial agents. Library screening efforts can be improved by increasing the information content of the screening effort. In this study, we screened the National Cancer Institute diversity set V against methicillin-resistant Staphylococcus aureus (MRSA) with several enhancements. One of these is to screen the library before and after microsomal metabolism as means to identify potential active metabolites. A second enhancement is to screen the library in the absence and presence of sub-minimum inhibitory concentration levels of another antibiotic, such as cefoxitin in this study. This identified four agents with synergistic activity with cefoxitin out of 16 agents with good MRSA activity alone. Finally, active agents from this effort were counter-screened in the presence of thymidine, which quickly identified three folate/thymidine biosynthesis inhibitors, and also screened for bactericidal vs bacteriostatic activity.

Prenylation: A Critical Step for Biomanufacturing of Prenylated Aromatic Natural Products

Prenylated aromatic natural products (PANPs) have received much attention due to their biomedical benefits for human health. The prenylation of aromatic natural products (ANPs), which is mainly catalyzed by aromatic prenyltransferases (aPTs), contributes significantly to their structural and functional diversity by providing higher lipophilicity and enhanced bioactivity. aPTs are widely distributed in bacteria, fungi, animals, and plants and play a key role in the regiospecific prenylation of ANPs. Recent studies have greatly advanced our understanding of the characteristics and application of aPTs. In this review, we comment on research progress regarding sources, evolutionary relationships, structural features, reaction mechanism, engineering modification, and application of aPTs. Particular emphasis is also placed on recent advances, challenges, and prospects about applications of aPTs in microbial cell factories for producing PANPs. Generally, this review could provide guidance for using aPTs as robust biocatalytic tools to produce various PANPs with high efficiency.

Structure and mechanism of the magnesium-independent aromatic prenyltransferase CloQ from the clorobiocin biosynthetic pathway

CloQ is an aromatic prenyltransferase from the clorobiocin biosynthetic pathway of Streptomyces roseochromogenes var. oscitans. It is involved in the synthesis of the prenylated hydroxybenzoate moiety of the antibiotic, specifically catalyzing the attachment of a dimethylallyl moiety to 4-hydroxyphenylpyruvate. Herein, we report the crystal structure of CloQ and use it as a framework for interpreting biochemical data from both wild-type and variant proteins. CloQ belongs to the aromatic prenyltransferase family, which is characterized by an unusual core fold comprising five consecutive ααββ elements that form a central 10-stranded anti-parallel β-barrel. The latter delineates a solvent-accessible cavity where substrates bind and catalysis takes place. This cavity has well-defined polar and nonpolar regions, which have distinct roles in substrate binding and facilitate a Friedel-Crafts-type mechanism. We propose that the juxtaposition of five positively charged residues in the polar region circumvents the necessity for a Mg(2+), which, by contrast, is a strict requirement for the majority of prenyltransferases characterized to date. Our structure of CloQ complexed with 4-hydroxyphenylpyruvate reveals the formation of a covalent link between the substrate and Cys215 to yield a thiohemiketal species. Through site-directed mutagenesis, we show that this link is not essential for enzyme activity in vitro. Furthermore, we demonstrate that CloQ will accept alternative substrates and, therefore, has the capacity to generate a range of prenylated compounds. Since prenylation is thought to enhance the bioactivity of many natural products, CloQ offers considerable promise as a biocatalyst for the chemoenzymatic synthesis of novel compounds with therapeutic potential.

Prenyl transfer to aromatic substrates in the biosynthesis of aminocoumarins, meroterpenoids and phenazines: the ABBA prenyltransferase family

Aromatic prenyltransferases transfer prenyl moieties onto aromatic acceptor molecules, catalyzing an electrophilic substitution of the aromatic ring under formation of carbon-carbon bonds. They give rise to an astounding diversity of primary and secondary metabolites in plants, fungi and bacteria. This review describes a recently discovered family of aromatic prenyltransferases. The structure of these enyzmes shows a type of beta/alpha fold with antiparallel beta strands. Due to the alpha-beta-beta-alpha architecture of this fold, this group of enzymes was designated as ABBA prenyltransferases. They lack the (N/D)DxxD motif which is characteristic for many other prenyltransferases. At present, 14 genes with sequence similarity to ABBA prenyltransferases can be identified in the database. A phylogenetic analysis of these genes separates them into two clades. One of them comprises the 4-hydroxyphenylpyruvate 3-dimethylallyltransferases CloQ and NovQ involved in aminocoumarin antibiotic biosynthesis in Streptomyces strains, as well as four genes of unknown function from fungal genomes. The other clade comprises genes involved in the biosynthesis of prenylated naphthoquinones and prenylated phenazines in different streptomycetes. ABBA prenyltransferases are soluble biocatalysts which can easily be obtained as homogeneous proteins in significant amounts. Their substrates are accommodated in a surprisingly spacious central cavity which explains their promiscuity for different aromatic substrates. Therefore, the enzymes of this family represent attractive tools for the chemoenzymatic synthesis of bioactive molecules.

Prenyl transfer to aromatic substrates: genetics and enzymology

Aromatic prenyltransferases catalyze the transfer of prenyl moieties to aromatic acceptor molecules and give rise to an astounding diversity of primary and secondary metabolites in plants, fungi and bacteria. Significant progress has been made in the biochemistry and genetics of this heterogeneous group of enzymes in the past years. After 30 years of extensive research on plant prenylflavonoid biosynthesis, finally the first aromatic prenyltransferases involved in the formation of these compounds have been cloned. In bacteria, investigations of the newly discovered family of ABBA prenyltransferases revealed a novel type of protein fold, the PT barrel. In fungi, a group of closely related indole prenyltransferase was found to carry out aromatic prenylations with different substrate specificity and regiospecificity, and to catalyze both regular and reverse prenylations.

A soluble, magnesium-independent prenyltransferase catalyzes reverse and regular C-prenylations and O-prenylations of aromatic substrates

Fnq26 from Streptomyces cinnamonensis DSM 1042 is a new member of the recently identified CloQ/Orf2 class of prenyltransferases. The enzyme was overexpressed in E. coli and purified to apparent homogeneity, resulting in a soluble, monomeric protein of 33.2 kDa. The catalytic activity of Fnq26 is independent of the presence of Mg(2+) or other divalent metal ions. With flaviolin (2,5,7-trihydroxy-1,4-naphthoquinone) as substrate, Fnq26 catalyzes the formation of a carbon-carbon-bond between C-3 (rather than C-1) of geranyl diphosphate and C-3 of flaviolin, i.e. an unusual "reverse" prenylation. With 1,3-dihydroxynaphthalene and 4-hydroxybenzoate as substrates Fnq26 catalyzes O-prenylations.