ABSTRACT. In the wake of the escalating development of resistance to currently available drugs, blocking the vital MEP pathway for isoprenoid biosynthesis in pathogens such as Plasmodia or Mycobacteria offers interesting prospects for inhibiting their growth. Although the natural product retro-hydroxamate fosmidomycin and its homologue FR900098 potently inhibit 1-deoxy-D-xylulose-5-phosphate reductoisomerase (Dxr), a key enzyme in the MEP pathway, their in vivo activity is compromised due to poor absorption and a suboptimal pharmacokinetic profile. In an effort to facilitate cellular uptake, we introduced aryl or aralkyl substituents at the β-position of the hydroxamate analogue of FR900098. While direct addition of a β-aryl moiety resulted in poor inhibition, longer linkers between the carbon backbone and the phenyl ring were generally associated with better binding to the enzymes, as well as activity against P. falciparum.X-ray structures of the parasite Dxr-inhibitor complexes show that the modes of binding of the two classes of compounds are in fact different. When the "shorter" compounds were bound, the active site flap was fully ordered and similar to that observed for the retro-hydroxamates. The "longer" compounds generate a substantially different flap structure, in which a key tryptophan residue is displaced, and the aromatic group of the ligand lies between the tryptophan and the methyl group on the hydroxamate. Although the most promising new Dxr inhibitors lack activity against E. coli and M. smegmatis, they proved to be highly potent inhibitors of Plasmodium falciparum in vitro growth.3

The antimalarial compound fosmidomycin targets DXR, the enzyme that catalyzes the first committed step in the MEP pathway producing the essential isoprenoid precursors, isopentenyl diphosphate and dimethylallyl diphosphate. The MEP pathway is used by a number of pathogens, including Mycobacterium tuberculosis and apicomplexan parasites, and differs from the classical mevalonate pathway that is essential in humans. Using a structure-based approach, we designed a number of analogues of fosmidomycin, including a series that are substituted in both the Cα and the hydroxamate positions. The latter proved to be a stable framework for the design of inhibitors that extend from the polar and cramped (and so not easily druggable) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 substrate-binding site and can, for the first time, bridge the substrate and cofactor binding sites.A number of these compounds are more potent than fosmidomycin in terms of killing Plasmodium falciparum in an in vitro assay; the best has an IC 50 of 40 nM. IntroductionFosmidomycin (1) and its acetyl derivative, , are natural product antibiotics with activity against a number of important pathogens. 1,2 They work by blocking the pathway for biosynthesis of isopentenyl diphosphate and dimethylallyl diphosphate that proceeds via the intermediate 2-C-methyl-D-erythritol 4-phosphate (MEP). This MEP pathway is used in Gramnegative and some Gram-positive bacteria, as well as in plant chloroplasts, algae and apicomplexan protozoa. 3 The enzymes involved are essential to the organisms possessing them, yet completely absent in humans, and they have therefore received considerable attention as potential targets for antimicrobial drug discovery. Fosmidomycin and 2 act by inhibiting the second (and first committed) step in the pathway, 4, 5 in which 1-deoxy-D-xylulose 5-phosphate (DXP) is converted to MEP by the enzyme 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR, also called IspC). A number of major pathogens are dependent upon the MEP pathway, although not all are sensitive to fosmidomycin and its analogues. For example, while both 1 and 2 inhibit the DXRs of the protozoan Plasmodium falciparum (PfDXR) 6 and Mycobacterium tuberculosis (MtDXR), 7-10 the Plasmodium species are sensitive to these antibiotics in vitro and in vivo, 6 but the mycobacteria are not. 11 The use of fosmidomycin as a single-drug treatment for P. falciparum malaria has been hampered by low bioavailability, rapid clearance from the parasite and recrudescent infection, 12 although the compound has been used more successfully in combination with clindamycin. 13 Failure to obtain biological activity against mycobacteria appears to result from poor uptake. 11Page 3 of 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34...

SynopsisEukaryotic cytosolic ACBPs (acyl-CoA-binding proteins) bind acyl-CoA esters and maintain a cytosolic acyl-CoA pool, but the thermodynamics of their protein-lipid interactions and physiological relevance in plants are not well understood. Arabidopsis has three cytosolic ACBPs which have been identified as AtACBP4, AtACBP5 and AtACBP6, and microarray data indicated that all of them are expressed in seeds; AtACBP4 is expressed in early embryogenesis, whereas AtACBP5 is expressed later. ITC (isothermal titration calorimetry) in combination with transgenic Arabidopsis lines were used to investigate the roles of these three ACBPs from Arabidopsis thaliana. The dissociation constants, stoichiometry and enthalpy change of AtACBP interactions with various acyl-CoA esters were determined using ITC. Strong binding of recombinant (r) AtACBP6 with long-chain acyl-CoA (C16-to C18-CoA) esters was observed with dissociation constants in the nanomolar range. However, the affinity of rAtACBP4 and rAtACBP5 to these acyl-CoA esters was much weaker (dissociation constants in the micromolar range), suggesting that they interact with acyl-CoA esters differently from rAtACBP6. When transgenic Arabidopsis expressing AtACBP6pro::GUS was generated, strong GUS (β-glucuronidase) expression in cotyledonary-staged embryos and seedlings prompted us to measure the acylCoA contents of the acbp6 mutant. This mutant accumulated higher levels of C18:1-CoA and C18:1-and C18:2-CoAs in cotyledonary-staged embryos and seedlings, respectively, in comparison with the wild type. The acbp4acbp5acbp6 mutant showed the lightest seed weight and highest sensitivity to abscisic acid during germination, suggesting their physiological functions in seeds.

Scots pine (Pinus sylvestris) secretes a number of small, highly-related, disulfide-rich proteins (Sp-AMPs) in response to challenges with fungal pathogens such as Heterobasidion annosum, although their biological role has been unknown. Here, we examined the expression patterns of these genes, as well as the structure and function of the encoded proteins. Northern blots and quantitative real time PCR showed increased levels of expression that are sustained during the interactions of host trees with pathogens, but not non-pathogens, consistent with a function in conifer tree defenses. Furthermore, the genes were up-regulated after treatment with salicylic acid and an ethylene precursor, 1-aminocyclopropane-1-carboxylic-acid, but neither methyl jasmonate nor H 2 O 2 induced expression, indicating that Sp-AMP gene expression is independent of the jasmonic acid signaling pathways. The cDNA encoding one of the proteins was cloned and expressed in Pichia pastoris. The purified protein had antifungal activity against H. annosum, and caused morphological changes in its hyphae and spores. It was directly shown to bind soluble and insoluble β-(1,3)-glucans, specifically and with high affinity. Furthermore, addition of exogenous glucan is linked to higher levels of Sp-AMP expression in the conifer. Homology modeling and sequence comparisons suggest that a conserved patch on the surface of the globular Sp-AMP is a carbohydrate-binding site that can accommodate approximately four sugar units. We conclude that these proteins belong to a new family of antimicrobial proteins that are likely to act by binding the glucans that are a major component of fungal cell walls.

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Source: ChemMedChem 2016ChemMedChem , 11, 2024 Targeting an aromatic hotspot in Plasmodium falciparum 1-deoxy-D-xylulose xylulose-5-phosphate reductoisomerase with- arylpropyl-analogues of fosmidomycinSanjeewani Sooriyaarachchi, Martijn D.P. Risseeuw, [b] Terese Bergfors, [a] Jenny Pouyez, [c] Cynthia S. Dowd, [d] Louis Maes, [e] Johan Wouters, [c] T. Alwyn Jones, [a] Serge Van Calenbergh *[b] and Sherry L. Mowbray show that all of the new arylpropyl substituents displace a key tryptophan residue of the active-site flap, which had made favorable interactions with 1 and 2. Plasticity of the flap allows substituents to be accommodated in many ways; in most cases, the flap is largely disordered. Compounds can be separated into two classes based on whether the substituent on the aromatic ring is meta or para. Generally, meta-compounds are better inhibitors, and in both classes, smaller size is linked to better potency.

Protein C inhibitor (PCI) is a serpin type of serine protease inhibitor that is found in many tissues and fluids in human, including blood plasma, seminal plasma and urine. This inhibitor displays an unusually broad protease specificity compared with other serpins. Previous studies have shown that the N-glycan(s) and the NH2-terminus affect some blood-related functions of PCI. In this study, we have for the first time determined the N-glycan profile of seminal plasma PCI, by mass spectrometry. The N-glycan structures differed markedly compared with those of both blood-derived and urinary PCI, providing evidence that the N-glycans of PCI are expressed in a tissue-specific manner. The most abundant structure (m/z 2592.9) had a composition of Fuc3Hex5HexNAc4, consistent with a core fucosylated bi-antennary glycan with terminal Lewisx. A major serine protease in semen, prostate specific antigen (PSA), was used to evaluate the effects of N-glycans and the NH2-terminus on a PCI function related to the reproductive tract. Second-order rate constants for PSA inhibition by PCI were 4.3±0.2 and 4.1±0.5 M−1s−1 for the natural full-length PCI and a form lacking six amino acids at the NH2-terminus, respectively, whereas these constants were 4.8±0.1 and 29±7 M−1s−1 for the corresponding PNGase F-treated forms. The 7–8-fold higher rate constants obtained when both the N-glycans and the NH2-terminus had been removed suggest that these structures jointly affect the rate of PSA inhibition, presumably by together hindering conformational changes of PCI required to bind to the catalytic pocket of PSA.