[show abstract][hide abstract] ABSTRACT: The DosR regulon in Mycobacterium tuberculosis is involved in respiration-limiting conditions, its induction is controlled by two histidine kinases, DosS and DosT, and recent experimental evidence indicates DosS senses either molecular oxygen or a redox change. Under aerobic conditions, induction of the DosR regulon by DosS, but not DosT, was observed after the addition of ascorbate, a powerful cytochrome c reductant, demonstrating that DosS responds to a redox signal even in the presence of high oxygen tension. During hypoxic conditions, regulon induction was attenuated by treatment with compounds that occluded electron flow into the menaquinone pool or decreased the size of the menaquinone pool itself. Increased regulon expression during hypoxia was observed when exogenous menaquinone was added, demonstrating that the menaquinone pool is a limiting factor in regulon induction. Taken together, these data demonstrate that a reduced menaquinone pool directly or indirectly triggers induction of the DosR regulon via DosS. Biochemical analysis of menaquinones upon entry into hypoxic/anaerobic conditions demonstrated the disappearance of the unsaturated species and low-level maintenance of the mono-saturated menaquinone. Relative to the unsaturated form, an analog of the saturated form is better able to induce signaling via DosS and rescue inhibition of menaquinone synthesis and is less toxic. The menaquinone pool is central to the electron transport system (ETS) and therefore provides a mechanistic link between the respiratory state of the bacilli and DosS signaling. Although this report demonstrates that DosS responds to a reduced ETS, it does not rule out a role for oxygen in silencing signaling.
Journal of bacteriology 10/2010; 192(24):6447-55. · 3.94 Impact Factor
[show abstract][hide abstract] ABSTRACT: Many pathogenic bacteria utilize the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for the biosynthesis of isopentenyl diphosphate and dimethylallyl diphosphate, two major building blocks of isoprenoid compounds. The fifth enzyme in the MEP pathway, 2-C-methyl-D-erythritol 2,4-cyclodiphosphate (ME-CPP) synthase (IspF), catalyzes the conversion of 4-diphosphocytidyl-2-C-methyl-D-erythritol 2-phosphate (CDP-ME2P) to ME-CPP with a corresponding release of cytidine 5-monophosphate (CMP). Because there is no ortholog of IspF in human cells, IspF is of interest as a potential drug target. However, study of IspF has been hindered by a lack of enantiopure CDP-ME2P. Herein, we report the first, to our knowledge, synthesis of enantiomerically pure CDP-ME2P from commercially available D-arabinose. Cloned, expressed, and purified M. tuberculosis IspF was able to utilize the synthetic CDP-ME2P as a substrate, a result confirmed by mass spectrometry. A convenient, sensitive, in vitro IspF assay was developed by coupling the CMP released during production of ME-CPP to mononucleotide kinase, which can be used for high throughput screening.
[show abstract][hide abstract] ABSTRACT: Many bacterial pathogens utilize the 2-C-methyl-D-erythritol 4-phosphate pathway for biosynthesizing isoprenoid precursors, a pathway that is vital for bacterial survival and absent from human cells, providing a potential source of drug targets. However, the characterization of 4-diphosphocytidyl-2-C-methyl-D-erythritol (CDP-ME) kinase (IspE) has been hindered due to a lack of enantiopure CDP-ME and difficulty in obtaining pure IspE. Here, enantiopure CDP-ME was chemically synthesized and recombinant IspE from bacterial pathogens were purified and characterized. Although gene disruption was not possible in Mycobacterium tuberculosis, IspE is essential in Mycobacterium smegmatis. The biochemical and kinetic characteristics of IspE provide the basis for development of a high throughput screen and structural characterization.
[show abstract][hide abstract] ABSTRACT: Understanding the basis of bacterial persistence in latent infections is critical for eradication of tuberculosis. Analysis of Mycobacterium tuberculosis mRNA expression in an in vitro model of non-replicating persistence indicated that the bacilli require electron transport chain components and ATP synthesis for survival. Additionally, low μM concentrations of aminoalkoxydiphenylmethane derivatives inhibited both the aerobic growth and survival of non-replicating, persistent M. tuberculosis. Metabolic labelling studies and quantification of cellular menaquinone levels suggested that menaquinone synthesis, and consequently electron transport, is the target of the aminoalkoxydiphenylmethane derivatives. This hypothesis is strongly supported by the observations that treatment with these compounds inhibits oxygen consumption and that supplementation of growth medium with exogenous menaquinone rescued both growth and oxygen consumption of treated bacilli. In vitro assays indicate that the aminoalkoxydiphenylmethane derivatives specifically inhibit MenA, an enzyme involved in the synthesis of menaquinone. Thus, the results provide insight into the physiology of mycobacterial persistence and a basis for the development of novel drugs that enhance eradication of persistent bacilli and latent tuberculosis.
[show abstract][hide abstract] ABSTRACT: Enantiomerically pure 2-C-methyl-D-erythritol 4-phosphate 1 (MEP) is synthesized from 1,2-O-isopropylidene-α-D-xylofuranose via facile benzylation in good yield. Subsequently, 1 is used for enzymatic synthesis of 4-diphosphocytidyl-2-C-methyl-D-erythritol 2 (CDP-ME) using 4-diphosphocytidyl-2-C-methyl-D-erythritol synthase (IspD). The chemoenzymatically synthesized 2 can be used as substrate for assay of IspE and for high throughput screening to identify IspE inhibitors.
[show abstract][hide abstract] ABSTRACT: Enantiomerically pure 2-C-methyl-D-erythritol 2,4-cyclodiphosphate 1 (ME-CPP) is synthesized from 1,2-O-isopropylidene-α-D-xylofuranose with facile phosphorylation in good yield. Subsequently, the synthesized enantiomerically pure 1 can be used as a substrate in IspG assays to identify inhibitors that may be developed into antibacterial drug leads.
[show abstract][hide abstract] ABSTRACT: Since utilization of menaquinone in the electron transport system is a characteristic of Gram-positive organisms, the 1,4-dihydroxy-2-naphthoate prenyltransferase (MenA) inhibitors 1a and 2a act as selective antibacterial agents against organisms such as methicillin-resistant Stapylococcus aureus (MRSA), Staphylococcus epidermidis (MRSE), and Mycobacterium spp. Growth of drug-resistant Gram-positive organisms was sensitive to the MenA inhibitors, indicating that menaquinone synthesis is a valid new drug target in Gram-positive organisms.
Journal of Medicinal Chemistry 09/2007; 50(17):3973-5. · 5.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: An efficient chemoenzymatic synthesis of UDP-N-acetylmuramyl-l-alanyl-γ-d-glutamyl-meso-diaminopimelyl-d-alanyl-d-alanine (Park’s nucleotide) is reported. UDP-MurNAc is efficiently synthesized by a minimum number of protecting strategies. One-pot amino acid ligation reactions catalyzed by MurC, D, E, and F enzymes are amenable to scale-up production.
Tetrahedron Letters - TETRAHEDRON LETT. 01/2007; 48(5):799-803.
[show abstract][hide abstract] ABSTRACT: An efficient synthesis of a versatile scaffold 3, anti-2-chloro-3- hydroxy ester can be achieved via a boron mediated diastereofacial anti-aldol reaction of 2-(N-methylbenzyl-N-2,4,6-trimethylbenzyl)-amino-1-phenylpropanol chloroester 1 and the uridyl aldehyde derivative 2. Generation of uridine-amino alcohol-based library is demonstrated by using the scaffold 3.