An enzyme-initiated Smiles rearrangement enables the development of an assay of MshB, the GlcNAc-Ins deacetylase of mycothiol biosynthesis

Diaryl Ether Formation by a Versatile Thioesterase Domain

Oxidative coupling and oxidative rearrangement are two of the most common biosynthetic strategies to form diaryl ethers. In contrast, enzymatic diaryl ether generation that proceeds in a nonoxidative manner has not been characterized thus far. Here, we discovered a versatile thioesterase (TE) domain from the nonreducing polyketide synthase (nrPKS) AN7909, which catalyzes diaryl ether formation through a series of successive steps involving esterification, a Smiles rearrangement, and hydrolysis. Further mutations and biochemical analyses with synthetic mimic substrates provide insight into the proposed catalytic process of the TE domain.

Functional Characterisation of Bile Metagenome: Study of Metagenomic Dark Matter

Gallbladder metagenome involves a wide range of unidentified sequences comprising the so-called metagenomic dark matter. Therefore, this study aimed to characterise three gallbladder metagenomes and a fosmid library with an emphasis on metagenomic dark matter fraction. For this purpose, a novel data analysis strategy based on the combination of remote homology and molecular modelling has been proposed. According to the results obtained, several protein functional domains were annotated in the metagenomic dark matter fraction including acetyltransferases, outer membrane transporter proteins, membrane assembly factors, DNA repair and recombination proteins and response regulator phosphatases. In addition, one deacetylase involved in mycothiol biosynthesis was found in the metagenomic dark matter fraction of the fosmid library. This enzyme may exert a protective effect in Actinobacteria against bile components exposure, in agreement with the presence of multiple antibiotic and multidrug resistance genes. Potential mechanisms of action of this novel deacetylase were elucidated by molecular simulations, highlighting the role of histidine and aspartic acid residues. Computational pipelines presented in this work may be of special interest to discover novel microbial enzymes which had not been previously characterised.

Stereoselective α-glycosylation of C(6)-hydroxyl myo-inositols via nickel catalysis-application to the synthesis of GPI anchor pseudo-oligosaccharides

Glycosylphosphatidyl inositol (GPI) anchors play a key role in many eukaryotic biological pathways. Stereoselective synthesis of GPI anchor analogues have proven to be critical for probing the biosynthesis, structure, and biological properties of these compounds. Challenges that have emerged from these efforts include the preparation of the selectively protected myo-inositol building blocks and the stereoselective construction of glucosamine α-linked myo-inositol containing pseudodisaccharide units. Herein, we describe the effectiveness of the cationic nickel(II) catalyst, Ni(4-F-PhCN)4(OTf)2, at promoting selective formation of 1,2-cis-2-amino glycosidic bonds between the C(2)-N-substituted benzylideneamino trihaloacetimidate donors and C(6)-hydroxyl myo-inositol acceptors. This catalytic coupling process allows rapid access to pseudosaccharides of GPI anchors in good yields and with excellent levels of α-selectivity (α:β=10:1-20:1). In stark contrast, activation of trichloroacetimidate donors containing the C(2)-N-substituted benzylidene group with TMSOTf and BF3(.)OEt2 provided the desired pseudodisaccharides as a 1:1 mixture of α- and β-isomers.

Pantothenamides are potent, on-target inhibitors of Plasmodium falciparum growth when serum pantetheinase is inactivated

Growth of the virulent human malaria parasite Plasmodium falciparum is dependent on an extracellular supply of pantothenate (vitamin B(5)) and is susceptible to inhibition by pantothenate analogues that hinder pantothenate utilization. In this study, on the hunt for pantothenate analogues with increased potency relative to those reported previously, we screened a series of pantothenamides (amide analogues of pantothenate) against P. falciparum and show for the first time that analogues of this type possess antiplasmodial activity. Although the active pantothenamides in this series exhibit only modest potency under standard in vitro culture conditions, we show that the potency of pantothenamides is selectively enhanced when the parasite culture medium is pre-incubated at 37°C for a prolonged period. We present evidence that this finding is linked to the presence in Albumax II (a serum-substitute routinely used for in vitro cultivation of P. falciparum) of pantetheinase activity: the activity of an enzyme that hydrolyzes the pantothenate metabolite pantetheine, for which pantothenamides also serve as substrates. Pantetheinase activity, and thereby pantothenamide degradation, is reduced following incubation of Albumax II-containing culture medium for a prolonged period at 37°C, revealing the true, sub-micromolar potency of pantothenamides. Importantly we show that the potent antiplasmodial effect of pantothenamides is attenuated with pantothenate, consistent with the compounds inhibiting parasite proliferation specifically by inhibiting pantothenate and/or CoA utilization. Additionally, we show that the pantothenamides interact with P. falciparum pantothenate kinase, the first enzyme involved in converting pantothenate to coenzyme A. This is the first demonstration of on-target antiplasmodial pantothenate analogues with sub-micromolar potency, and highlights the potential of pantetheinase-resistant pantothenamides as antimalarial agents.

Nickel-catalyzed α-glycosylation of C(1)-hydroxyl D-myo-inositol: a formal synthesis of mycothiol

Formal synthesis of mycothiol has been developed via nickel-catalyzed α-glycosylation of the C(1)-hydroxyl group of D-myo-inositols with C(2)-N-substituted benzylideneamino N-phenyl trifluoroacetimidate donors. The pseudo-oligosaccharides were obtained in good yield and with excellent α-selectivity. Removal of the C(2)-N-2-trifluoromethylphenyl-benzylidene group under mild conditions provides a pseudo-disaccharide, completing the formal synthesis of mycothiol.