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Benzothiophene derivatives like benzothiophene sulphonamides, biphenyls, or carboxyls have been synthesized and have found wide pharmacological usage. Here we report, bromo-benzothiophene carboxamide derivatives as potent, slow tight binding inhibitors of Plasmodium enoyl-acyl carrier protein (ACP) reductase (PfENR). 3-Bromo- N-(4-fluorobenzyl)-benzo[b]thiophene-2-carboxamide (compound 6) is the most potent inhibitor with an IC50 of 115 nM for purified PfENR. The inhibition constant ( Ki) of compound 6 was 18 nM with respect to the cofactor and 91 nM with respect to crotonoyl-CoA. These inhibitors showed competitive kinetics with cofactor and uncompetitive kinetics with the substrate. Thus, these compounds hold promise for the development of potent antimalarials. © 2011 IUBMB IUBMB Life, 63(12): 1101-1110, 2011 [ABSTRACT FROM AUTHOR]

Abstract: Epigallocatechin gallate (EGCG) is known to have numerous pharmacological properties. In the present study, we have shown that EGCG inhibits enoyl–acyl carrier protein reductase of Plasmodium falciparum (PfENR) by following a two-step, slow, tight-binding inhibition mechanism. The association/isomerization rate constant (k 5) of the reversible and loose PfENR–EGCG binary complex to a tight [PfENR–EGCG]∗ or EI∗ complex was calculated to be 4.0×10−2 s−1. The low dissociation rate constant (k 6) of the [PfENR–EGCG]∗ complex confirms the tight-binding nature of EGCG. EGCG inhibited PfENR with the overall inhibition constant (K i ∗) of 7.0±0.8nM. Further, we also studied the effect of triclosan on the inhibitory activity of EGCG. Triclosan lowered the k 6 of the EI∗ complex by 100 times, lowering the overall K i ∗ of EGCG to 97.5±12.5 pM. The results support EGCG as a promising candidate for the development of tea catechin based antimalarial drugs. [Copyright &y& Elsevier]

Acyl Carrier Protein (ACP) from the malaria parasite, Plasmodium falciparum (PfACP) in its holo form is found to exist in two conformational states in solution. Unique 3D solution structures of holo-PfACP have been determined for both equilibrium conformations, using high-resolution NMR methods. Twenty high-resolution solution structures for each of the two forms of holo-PfACP have been determined on the basis of 1226 and 1218 unambiguously assigned NOEs (including NOEs between 4‰-phosphopantetheine prosthetic group (4‰-PP) and protein), 55 backbone dihedral angles and 26 hydrogen bonds. The atomic rmsd values of the determined structures of two equilibrium forms, about the mean coordinates of the backbone and heavy atoms, are 0.48 ± 0.09 and 0.92 ± 0.10 and 0.49 ± 0.08 and 0.97 ± 0.11 Å, respectively. The interaction of 4‰-PP with the polypeptide backbone is reported here for the first time for any of the ACPs. The structures of holo-PfACP consist of three well-defined helices that are tightly packed. The structured regions of the molecule are stabilized by extensive hydrophobic interactions. The difference between the two forms arises from a reorientation of the 4‰-PP group. The enthalpy difference between the two forms, although small, implies that a conformational switch is essential for the activation of holo-ACP. Sequence and structures of holo-PfACP have been compared with those of the ACPs from type I and type II fatty acid biosynthesis pathways (FAS), in particular with the ACP from rat and the butyryl-ACP from E. coli. The PfACP structure, thus determined has several novel features hitherto not seen in other ACPs. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure of β-hydroxyacyl acyl carrier protein dehydratase of Plasmodium falciparum (PfFabZ) has been determined at a resolution of 2.4Å. PfFabZ has been found to exist as a homodimer (d-PfFabZ) in the crystals of the present study in contrast to the reported hexameric form (h-PfFabZ) which is a trimer of dimers crystallized in a different condition. The catalytic sites of this enzyme are located in deep narrow tunnel-shaped pockets formed at the dimer interface. A histidine residue from one subunit of the dimer and a glutamate residue from the other subunit lining the tunnel form the catalytic dyad in the reported crystal structures. While the position of glutamate remains unaltered in the crystal structure of d-PfFabZ compared to that in h-PfFabZ, the histidine residue takes up an entirely different conformation and moves away from the tunnel leading to a His-Phe cis–trans peptide flip at the histidine residue. In addition, a loop in the vicinity has been observed to undergo a similar flip at a Tyr–Pro peptide bond. These alterations not only prevent the formation of a hexamer but also distort the active site geometry resulting in a dimeric form of FabZ that is incapable of substrate binding. The dimeric state and an altered catalytic site architecture make d-PfFabZ distinctly different from the FabZ structures described so far. Dynamic light scattering and size exclusion chromatographic studies clearly indicate a pH-related switching of the dimers to active hexamers. [Copyright &y& Elsevier]

Abstract: Acyl carrier protein (ACP) plays a central role in fatty acid biosynthesis by transferring the acyl groups from one enzyme to another for the completion of the fatty acid synthesis cycle. Holo-ACP is the obligatory substrate for the synthesis of acyl-ACPs which act as the carrier and donor for various metabolic reactions. Despite its interactions with numerous proteins in the cell, its mode of interaction is poorly understood. Here, we report the over-expression of PfACP in minimal medium solely in its holo form and in high yield. Expression in minimal media provides a means to isotopically label PfACP for high resolution multi-nuclear and multi-dimensional NMR studies. Indeed, the proton–nitrogen correlated NMR spectrum exhibits very high chemical shift dispersion and resolution. We also show that holo-PfACP thus expressed is amenable to acylation reactions using Escherichia coli acyl-ACP synthetase as well as by standard chemical methods. [Copyright &y& Elsevier]

Presents letters to the editor discussing nuclear magnetic resonance assignments of peptide complex and holo-acyl carrier protein from malaria parasite Plasmodium falciparum. Discussion on Bcl-2 family of proteins; Role of peptides derived from the BH3 domains of pro-apoptotic Bcl-2 family members; Function of acyl carrier proteins in fatty acid biosynthesis.