The antibiotic micrococcin is a potent inhibitor of growth and protein synthesis in the malaria parasite

To quest new targets of Plasmodium parasite and their potential inhibitors to combat antimalarial drug resistance

Malaria remains a global health challenge with significant mortality and morbidity annually, with resistant parasite strains complicating treatment efforts. There is an acute need for novel antimalarial drugs that can put a stop to the future public health crisis caused by the multi-drug resistance strains of the Plasmodium parasite. However, the discovery of these new components is very challenging in the context of the generation of multi-drug resistance properties of malaria. The novel drugs also need to have several properties involving enhanced therapeutic prospects, successful treatment capabilities, and novel mechanisms of action that will forestall the resistance. To successfully achieve this aim researchers are trying to focus on exploring promising malaria targets. Various approaches have been made for the development of drugs for malaria including the remodelling of existing drugs and the development of novel inhibitors which acts on new targets. Advancement in the study provides more information on the biology of parasites and the new targets which help in the development of novel drugs. The present review focuses on the study of novel targets of malaria parasites and subsequent inhibitors of those particular targets. Some of these targets include malarial protease, various transporter proteins, enzymes involved in the synthesis of DNA, and nucleic acids like dihydroorotate dehydrogenase, dihydrofolate reductase, apicoplast and dihydropteroate synthase. Other potential targets are also included in this review such as isoprenoid biosynthesis, farnesyl transferase of parasite, P. falciparum translational elongation factor 2, and phosphatidyl inositol 4 kinase. These promising targets have also been summed up along with their corresponding inhibitors for combating multi-drug resistance malaria.

Heterologous Synthesis and Characterization of Thiocillin IV

Micrococcin P1 and P2 are thiopeptides with a wide range of biological functions including antibacterial and antimalarial activities. We previously demonstrated optimized enzymatic sequences for the exclusive and scalable biosynthesis of micrococcin P2. Thiocillin IV is predicted to be the congener of O-methylated micrococcin P2, but the exact structure has not been elucidated. In this study, we report the first scalable biosynthesis and full structural characterization of thiocillin IV, a 26-membered thiopeptide. This was achieved by generating a recombinant plasmid by inserting tclO, a gene encoding an O-methyltransferase, and genes responsible for micrococcin P2 production and incorporating them into a Bacillus strain. With the incorporation of precursor peptide genes and optimal culture conditions, production reached 2.4 mg/L of culture. The purified thiocillin IV structure was identified as O-methylated micrococcin P2 at the 8-Thr position, and its promising biological activity toward various Gram-positive pathogens was observed. This study provides tclO-mediated site-selective methylation and opens a biotechnological opportunity to produce selective thiopeptides.

Micrococcus spp. as a promising source for drug discovery: A review

Historically, bacteria of the phylum, Actinobacteria have been a very prominent source of bioactive compounds for drug discovery. Among the actinobacterial genera, Micrococcus has not generally been prioritized in the search for novel drugs. The bacteria in this genus are known to have very small genomes (generally < 3 Mb). Actinobacteria with small genomes seldom contain the well-characterized biosynthetic gene clusters such as those encoding polyketide synthases and nonribosomal peptide synthetases that current genome mining algorithms are optimized to detect. Nevertheless, there are many reports of substantial pharmaceutically relevant bioactivity of Micrococcus extracts. On the other hand, there are remarkably few descriptions of fully characterized and structurally elucidated bioactive compounds from Micrococcus spp. This review provides a comprehensive summary of the bioactivity of Micrococcus spp. that encompasses antibacterial, antifungal, cytotoxic, antioxidant, and anti-inflammatory activities. This review uncovers the considerable biosynthetic potential of this genus and highlights the need for a re-examination of these bioactive strains, with a particular emphasis on marine isolates, because of their potent bioactivity and high potential for encoding unique molecular scaffolds.

Geninthiocins E and F, two new cyclic thiopeptides with antiviral activities from soil-derived Streptomyces sp. CPCC 200267 using OSMAC strategy

On the basis of the one strain-many compounds (OSMAC) strategy, two new cyclic thiopeptides, geninthiocins E and F, together with four known geninthiocin derivatives, geninthiocins A, B, C, and val-geninthiocin were isolated from Streptomyces sp. CPCC 200267. Their structures and absolute configurations were elucidated by extensive spectroscopic analyses and Marfey's method. Geninthiocin E (1), val-geninthiocin (3), geninthiocin A (4), and geninthiocin B (5) exhibited significant anti-influenza A virus activities with the IC50 values of 28.7, 15.3, 7.3, and 18.3 μM, respectively. Compounds 3 and 4 showed moderate antibacterial activities against Staphylococcus aureus.

Antimicrobial peptides: natural or synthetic defense peptides against HBV and HCV infections

According to the literature, treatment of HCV and HBV infections faces challenges due to problems such as the emergence of drug-resistant mutants, the high cost of treatment, and the side effects of current antiviral therapy. Antimicrobial peptides (AMPs), a group of small peptides, are a part of the immune system and are considered as an alternative treatment for microbial infections. These peptides are water-soluble with amphiphilic (hydrophilic and hydrophobic surfaces) characteristics. AMPs are produced by a wide range of organisms including both prokaryotic and eukaryotic cells. The antiviral mechanisms of AMPs include inhibiting virus entry, inhibiting intracellular virus replication, inhibiting intracellular viral packaging, and inducing immune responses. In addition, AMPs are a new generation of antiviral biomolecules that have very low toxicity for human host cells, particularly liver cell lines. AMPs can be considered as one of the most important strategies for developing new adjuvant drugs in the treatment of HBV and HCV infections. In the present study, several groups of AMPs (with a net positive charge) such as Human cathelicidin, Claudin-1, Defensins, Hepcidin, Lactoferrin, Casein, Plectasin, Micrococcin P1, Scorpion venom, and Synthetic peptides were reviewed with antiviral properties against HBV and HCV.

Bacteriocins Revitalize Non-Effective Penicillin G to Overcome Methicillin-Resistant Staphylococcus pseudintermedius

The rise of antibiotic-resistant bacteria is among the biggest challenges in human and veterinary medicine. One of the major factors that contributes to resistance is use of frontline clinical antibiotics in veterinary practices. To avoid this problem, searching for antimicrobials aimed at veterinary applications is becoming especially important. Thiopeptide micrococcin P1 and leaderless peptide EntEJ97s are two different bacteriocins that are very active against many gram-positive bacteria; however, sensitive bacteria can rapidly develop resistance towards those bacteriocins. To overcome this problem, we searched for synergy between those bacteriocins and conventional antibiotics against methicillin-resistant Staphylococcus pseudintermedius (MRSP): a common pathogen in animal skin infections. The two bacteriocins acted synergistically with each other and with penicillin G against MRSP clinical isolates in both planktonic and biofilm assays; they also prevented resistance development. The therapeutic potential was further validated in a murine skin infection model that showed that a combination of micrococcin P1, EntEJ97s and penicillin G reduced cell-forming units of MRSP by 2-log10 CFU/g. Taken together, our data show that a combination of bacteriocins with conventional antibiotics can not only prevent resistance development but also pave the way to revitalize some old, less useful antibiotics, such as penicillin, which by itself has no effect on methicillin-resistant pathogens.

Mechanism of Action of Ribosomally Synthesized and Post-Translationally Modified Peptides

Ribosomally synthesized and post-translationally modified peptides (RiPPs) are a natural product class that has undergone significant expansion due to the rapid growth in genome sequencing data and recognition that they are made by biosynthetic pathways that share many characteristic features. Their mode of actions cover a wide range of biological processes and include binding to membranes, receptors, enzymes, lipids, RNA, and metals as well as use as cofactors and signaling molecules. This review covers the currently known modes of action (MOA) of RiPPs. In turn, the mechanisms by which these molecules interact with their natural targets provide a rich set of molecular paradigms that can be used for the design or evolution of new or improved activities given the relative ease of engineering RiPPs. In this review, coverage is limited to RiPPs originating from bacteria.

Antimalarial Natural Products

Natural products have made a crucial and unique contribution to human health, and this is especially true in the case of malaria, where the natural products quinine and artemisinin and their derivatives and analogues, have saved millions of lives. The need for new drugs to treat malaria is still urgent, since the most dangerous malaria parasite, Plasmodium falciparum, has become resistant to quinine and most of its derivatives and is becoming resistant to artemisinin and its derivatives. This volume begins with a short history of malaria and follows this with a summary of its biology. It then traces the fascinating history of the discovery of quinine for malaria treatment and then describes quinine's biosynthesis, its mechanism of action, and its clinical use, concluding with a discussion of synthetic antimalarial agents based on quinine's structure. The volume then covers the discovery of artemisinin and its development as the source of the most effective current antimalarial drug, including summaries of its synthesis and biosynthesis, its mechanism of action, and its clinical use and resistance. A short discussion of other clinically used antimalarial natural products leads to a detailed treatment of other natural products with significant antiplasmodial activity, classified by compound type. Although the search for new antimalarial natural products from Nature's combinatorial library is challenging, it is very likely to yield new antimalarial drugs. The chapter thus ends by identifying over ten natural products with development potential as clinical antimalarial agents.

The bacterial thiopeptide thiostrepton. An update of its mode of action, pharmacological properties and applications

The bacterial thiopeptide thiostrepton (TS) is used as a veterinary medicine to treat bacterial infections. TS is a protein translation inhibitor, essentially active against Gram-positive bacteria and some Gram-negative bacteria. In procaryotes, TS abrogates binding of GTPase elongation factors to the 70S ribosome, by altering the structure of rRNA-L11 protein complexes. TS exerts also antimalarial effects by disrupting protein synthesis in the apicoplast genome of Plasmodium falciparum. Interestingly, the drug targets both the infectious pathogen (bacteria or parasite) and host cell, by inducing endoplasmic reticulum stress-mediated autophagy which contributes to enhance the host cell defense. In addition, TS has been characterized as a potent chemical inhibitor of the oncogenic transcription factor FoxM1, frequently overexpressed in cancers or other diseases. The capacity of TS to crosslink FoxM1, and a few other proteins such as peroxiredoxin 3 (PRX3) and the 19S proteasome, contributes to the anticancer effects of the thiopeptide. The anticancer activities of TS evidenced using diverse tumor cell lines, in vivo models and drug combinations are reviewed here, together with the implicated targets and mechanisms. The difficulty to formulate TS is a drag on the pharmaceutical development of the natural product. However, the design of hemisynthetic analogues and the use of micellar drug delivery systems should facilitate a broader utilization of the compound in human and veterinary medicines. This review shed light on the many pharmacological properties of TS, with the objective to promote its use as a pharmacological tool and medicinal product.

Host-dependent heterologous expression of berninamycin gene cluster leads to linear thiopeptide antibiotics

Berninamycins are a class of thiopeptide antibiotics with potent activity against Gram-positive bacteria. Heterologous expression of the berninamycin (ber) biosynthetic gene cluster from marine-derived Streptomyces sp. SCSIO 11878 in different terrestrial model Streptomyces hosts led to the production of berninamycins A (1) and B (2) in Streptomyces lividans SBT18 and Streptomyces coelicolor M1154, while two new linearized berninamycins J (3) and K (4) were obtained in Streptomyces albus J1074. Their structures were elucidated by detailed interpretation of NMR data and Marfey's method. Bioactivity assays showed that the linear thiopeptides 3 and 4 were less potent than 1 and 2 in antibacterial activity. This work indicates that undefined host-dependent enzymes might be responsible for generating the linear thiopeptides 3 and 4 in S. albus J1074.

Bacterial natural products in the fight against mosquito-transmitted tropical diseases

Covering: up to 2019 Secondary metabolites of microbial origin have long been acknowledged as medically relevant, but their full potential remains largely unexploited. Of the countless natural compounds discovered thus far, only 5-10% have been isolated from microorganisms. At the same time, while whole-genome sequencing has demonstrated that bacteria and fungi often encode natural products, only a few genera have yet been mined for new compounds. This review explores the contributions of bacterial natural products to combatting infection by malaria parasites, filarial worms, and arboviruses such as dengue, Zika, Chikungunya, and West Nile. It highlights how molecules isolated from microorganisms ranging from marine cyanobacteria to mosquito endosymbionts can be exploited as antimicrobials and antivirals. Pursuit of this mostly untapped source of chemical entities will potentially result in new interventions against these tropical diseases, which are urgently needed to combat the increase in the incidence of resistance.

Staphylococcins: an update on antimicrobial peptides produced by staphylococci and their diverse potential applications

Staphylococcins are antimicrobial peptides or proteins produced by staphylococci. They can be separated into different classes, depending on their amino acid composition, structural complexity, and steps involved in their production. In this review, an overview of the current knowledge on staphylococcins will be presented with emphasis on the information collected in the last decade, including a brief description of new peptides. Most staphylococcins characterized to date are either lantibiotics or linear class II bacteriocins. Recently, gene clusters coding for production of circular bacteriocins, sactipeptides, and thiopeptides have been mined from the genome of staphylococcal isolates. In contrast to class II bacteriocins, lantibiotics, sactipeptides, and thiopeptides undergo post-translational modifications that can be quite extensive, depending on the peptide. Few staphylococcins inhibit only some staphylococcal species, but most of them have proven to target pathogens belonging to different genera and involved in a variety of infectious diseases of clinical or agronomic importance. Therefore, these peptides exhibit potential application as anti-infective drugs in different areas. This review will also cover this diverse and remarkable potential. To be commercialized, however, staphylococcin production should be cost-effective and result in high bacteriocin yields, which are not generally achieved from the culture supernatant of their native producers. Such low yields make their production quite costly and not suitable at large industrial scale. Efforts already made to overcome this limitation, minimizing costs and time of production of some staphylococcins and employing either chemical synthesis or in vivo biosynthesis, will be addressed in this review as well. KEY POINTS: • Staphylococci produce a variety of antimicrobial peptides known as staphylococcins. • Most staphylococcins are post-translationally modified peptides. • Staphylococcins exhibit potential biotechnological applications. Graphical abstract.

The Plasmodium falciparum cytoplasmic translation apparatus: a promising therapeutic target not yet exploited by clinically approved anti-malarials

BACKGROUND

The continued spectre of resistance to existing anti-malarials necessitates the pursuit of novel targets and mechanisms of action for drug development. One class of promising targets consists of the 80S ribosome and its associated components comprising the parasite translational apparatus. Development of translation-targeting therapeutics requires a greater understanding of protein synthesis and its regulation in the malaria parasite. Research in this area has been limited by the lack of appropriate experimental methods, particularly a direct measure of parasite translation.

METHODS

An in vitro method directly measuring translation in whole-cell extracts from the malaria parasite Plasmodium falciparum, the PfIVT assay, and a historically-utilized indirect measure of translation, S35-radiolabel incorporation, were compared utilizing a large panel of known translation inhibitors as well as anti-malarial drugs.

RESULTS

Here, an extensive pharmacologic assessment of the PfIVT assay is presented, using a wide range of known inhibitors demonstrating its utility for studying activity of both ribosomal and non-ribosomal elements directly involved in translation. Further, the superiority of this assay over a historically utilized indirect measure of translation, S35-radiolabel incorporation, is demonstrated. Additionally, the PfIVT assay is utilized to investigate a panel of clinically approved anti-malarial drugs, many with unknown or unclear mechanisms of action, and show that none inhibit translation, reaffirming Plasmodium translation to be a viable alternative drug target. Within this set, mefloquine is unambiguously found to lack translation inhibition activity, despite having been recently mischaracterized as a ribosomal inhibitor.

CONCLUSIONS

This work exploits a direct and reproducible assay for measuring P. falciparum translation, demonstrating its value in the continued study of protein synthesis in malaria and its inhibition as a drug target.

Antimicrobial, anticoagulant, and cytotoxic evaluation of multidrug resistance of new 1,4-dihydropyridine derivatives

A new series of 1,4-dihydropyridine derivatives (2a–h, 3a–e, and 4a–e) were systematically designed and synthesized via ultrasound irradiation methods with easy work-up and good yields. Compounds structures were confirmed by IR, ¹H NMR, ¹³C NMR, and mass spectra. The synthesized compounds were screened for both antimicrobial and anticoagulant activities. Compound 2e (MIC: 0.25 μg/mL) was highly active against Escherichia coli and compound 2c (MIC: 0.5 μg/mL) was also highly active against Pseudomonas aeruginosa compared with ciprofloxacin. (MIC: 1 μg/mL) The antifungal activity of 2c (MIC: 0.5 μg/mL) against Candida albicans was high relative to that of clotrimazole (MIC: 1 μg/mL). Anticoagulant activity was determined by activated partial thromboplastin time (APTT) and prothrombin time (PT) coagulation assays. Compound 4-(4-hydroxyphenyl)-2,6-dimethyl-N³,N⁵-bis(5-phenyl-1,3,4-thiadiazol-2-yl)-1,4-dihydropyridine-3,5-dicarboxamide 3d (>1000 s in APTT assays) was highly active in anticoagulant screening compared with the reference of heparin.

Cytotoxicity was evaluated using HepG2 (liver), HeLa (cervical), and MCF-7 (breast) cancer cell lines, with high toxicities observed for 2c (GI₅₀ = 0.02 μm) against HeLa cell line and 2e (GI₅₀ = 0.03 μm) equipotant against MCF-7 cell line. Therefore, the compounds 2e, 2c and 3d can serve as lead molecules for the development of new classes of antimicrobial and anticoagulant agent.

YcaO-Dependent Posttranslational Amide Activation: Biosynthesis, Structure, and Function

With advances in sequencing technology, uncharacterized proteins and domains of unknown function (DUFs) are rapidly accumulating in sequence databases and offer an opportunity to discover new protein chemistry and reaction mechanisms. The focus of this review, the formerly enigmatic YcaO superfamily (DUF181), has been found to catalyze a unique phosphorylation of a ribosomal peptide backbone amide upon attack by different nucleophiles. Established nucleophiles are the side chains of Cys, Ser, and Thr which gives rise to azoline/azole biosynthesis in ribosomally synthesized and posttranslationally modified peptide (RiPP) natural products. However, much remains unknown about the potential for YcaO proteins to collaborate with other nucleophiles. Recent work suggests potential in forming thioamides, macroamidines, and possibly additional post-translational modifications. This review covers all knowledge through mid-2016 regarding the biosynthetic gene clusters (BGCs), natural products, functions, mechanisms, and applications of YcaO proteins and outlines likely future research directions for this protein superfamily.

Synthesis, in vitro β-glucuronidase inhibitory activity and in silico studies of novel (E)-4-Aryl-2-(2-(pyren-1-ylmethylene)hydrazinyl)thiazoles

Current research is based on the synthesis of novel (E)-4-aryl-2-(2-(pyren-1-ylmethylene)hydrazinyl)thiazole derivatives (3-15) by adopting two steps route. First step was the condensation between the pyrene-1-carbaldehyde (1) with the thiosemicarbazide to afford pyrene-1-thiosemicarbazone intermediate (2). While in second step, cyclization between the intermediate (2) and phenacyl bromide derivatives or 2-bromo ethyl acetate was carried out. Synthetic derivatives were structurally characterized by spectroscopic techniques such as EI-MS, ¹H NMR and ¹³C NMR. Stereochemistry of the iminic double bond was confirmed by NOESY analysis. All pure compounds 2-15 were subjected for in vitro β-glucuronidase inhibitory activity. All molecules were exhibited excellent inhibition in the range of IC₅₀=3.10±0.10-40.10±0.90μM and found to be even more potent than the standard d-saccharic acid 1,4-lactone (IC₅₀=48.38±1.05μM). Molecular docking studies were carried out to verify the structure-activity relationship. A good correlation was perceived between the docking study and biological evaluation of active compounds.

Antibiotics in malaria therapy: which antibiotics except tetracyclines and macrolides may be used against malaria?

Malaria, a parasite vector-borne disease, is one of the most significant health threats in tropical regions, despite the availability of individual chemoprophylaxis. Malaria chemoprophylaxis and chemotherapy remain a major area of research, and new drug molecules are constantly being developed before drug-resistant parasites strains emerge. The use of anti-malarial drugs is challenged by contra-indications, the level of resistance of Plasmodium falciparum in endemic areas, clinical tolerance and financial cost. New therapeutic approaches are currently needed to fight against this disease. Some antibiotics that have shown potential effects on malaria parasite have been recently studied in vitro or in vivo intensively. Two families, tetracyclines and macrolides and their derivatives have been particularly studied in recent years. However, other less well-known have been tested or are being used for malaria treatment. Some of these belong to older families, such as quinolones, co-trimoxazole or fusidic acid, while others are new drug molecules such as tigecycline. These emerging antibiotics could be used to prevent malaria in the future. In this review, the authors overview the use of antibiotics for malaria treatment.

Micrococcin P1, a naturally occurring macrocyclic peptide inhibiting hepatitis C virus entry in a pan-genotypic manner

Hepatitis C virus (HCV) is considered a major public health concern worldwide. Despite recent advances in curing chronic hepatitis C, unmet medical needs still remain, especially due to the high economic burden of therapies. Accordingly, our study aimed to identify affordable novel HCV inhibitors by screening of natural product compound libraries. We identified micrococcin P1, a macrocyclic peptide antibiotic, inhibiting HCV entry in a pan-genotypic manner with an EC50 range of 0.1-0.5 μM. Micrococcin P1 interfered with HCV entry at an attachment step. Furthermore, micrococcin P1 efficiently inhibited HCV spread by blocking cell-free infection as well as cell-to-cell transmission, without affecting the secretion of infectious virions. Interestingly, the putative molecular target of micrococcin P1 is glycoprotein E2 (IIe-630-Thr), as revealed by selection for viral drug resistance. In addition, micrococcin P1 inhibited sofosbuvir-resistant HCV strains and showed synergy in combination with selected HCV drugs, suggesting an alternative treatment paradigm for patients. In conclusion, we identified micrococcin P1 as specifically inhibiting entry of all HCV genotypes and demonstrated that micrococcin P1 potentially could add value to therapies in combination with current HCV interventions.

Cyclisation mechanisms in the biosynthesis of ribosomally synthesised and post-translationally modified peptides

Ribosomally synthesised and post-translationally modified peptides (RiPPs) are a large class of natural products that are remarkably chemically diverse given an intrinsic requirement to be assembled from proteinogenic amino acids. The vast chemical space occupied by RiPPs means that they possess a wide variety of biological activities, and the class includes antibiotics, co-factors, signalling molecules, anticancer and anti-HIV compounds, and toxins. A considerable amount of RiPP chemical diversity is generated from cyclisation reactions, and the current mechanistic understanding of these reactions will be discussed here. These cyclisations involve a diverse array of chemical reactions, including 1,4-nucleophilic additions, [4 + 2] cycloadditions, ATP-dependent heterocyclisation to form thiazolines or oxazolines, and radical-mediated reactions between unactivated carbons. Future prospects for RiPP pathway discovery and characterisation will also be highlighted.

Saturation mutagenesis of TsrA Ala4 unveils a highly mutable residue of thiostrepton A

Thiopeptides are post-translationally processed macrocyclic peptide metabolites, characterized by extensive backbone and side chain modifications that include a six-membered nitrogeneous ring, thiazol(in)e/oxazol(in)e rings, and dehydrated amino acid residues. Thiostrepton A, one of the more structurally complex and well-studied thiopeptides, contains a second macrocycle bearing a quinaldic acid moiety. Antibacterial, antimalarial, and anticancer properties have been described for thiostrepton A and other thiopeptides, although the molecular details for binding the cellular target in each case are not fully elaborated. We previously demonstrated that a mutation of the TsrA core peptide, Ala4Gly, supported the successful production of the corresponding thiostrepton variant. To more thoroughly probe the thiostrepton biosynthetic machinery's tolerance toward structural variation at the fourth position of the TsrA core peptide, we report here the saturation mutagenesis of this residue using a fosmid-dependent biosynthetic engineering method and the isolation of 16 thiostrepton analogues. Several types of side chain substitutions at the fourth position of TsrA, including those that introduce polar or branched hydrophobic residues are accepted, albeit with varied preferences. In contrast, proline and amino acid residues inherently charged at physiological pH are not well-tolerated at the queried site by the thiostrepton biosynthetic system. These newly generated thiostrepton analogues were assessed for their antibacterial activities and abilities to inhibit the proteolytic functions of the eukaryotic 20S proteasome. We demonstrate that the identity of the fourth amino acid residue in the thiostrepton scaffold is not critical for either ribosome or proteasome inhibition.

In vitro antimalarial activity of novel semisynthetic nocathiacin I antibiotics

Presently, the arsenal of antimalarial drugs is limited and needs to be replenished. We evaluated the potential antimalarial activity of two water-soluble derivatives of nocathiacin (BMS461996 and BMS411886) against the asexual blood stages of Plasmodium falciparum. Nocathiacins are a thiazolyl peptide group of antibiotics, are structurally related to thiostrepton, have potent activity against a wide spectrum of multidrug-resistant Gram-positive bacteria, and inhibit protein synthesis. The in vitro growth inhibition assay was done using three laboratory strains of P. falciparum displaying various levels of chloroquine (CQ) susceptibility. Our results indicate that BMS461996 has potent antimalarial activity and inhibits parasite growth with mean 50% inhibitory concentrations (IC50s) of 51.55 nM for P. falciparum 3D7 (CQ susceptible), 85.67 nM for P. falciparum Dd2 (accelerated resistance to multiple drugs [ARMD]), and 99.44 nM for P. falciparum K1 (resistant to CQ, pyrimethamine, and sulfadoxine). Similar results at approximately 7-fold higher IC50s were obtained with BMS411886 than with BMS461996. We also tested the effect of BMS491996 on gametocytes; our results show that at a 20-fold excess of the mean IC50, gametocytes were deformed with a pyknotic nucleus and growth of stage I to IV gametocytes was arrested. This preliminary study shows a significant potential for nocathiacin analogues to be developed as antimalarial drug candidates and to warrant further investigation.

Molecular structure, vibrational and electronic properties of 4-Phenyl-3H-1,3-thiazol-2-ol using density functional theory and comparison of drug efficacy of keto and enol forms by QSAR analysis

4-Phenyl-3H-1,3-thiazol-2-ol can exist in two tautomeric forms - keto and enol. Comprehensive investigation of molecular geometry and electronic structure in ground as well as in the first excited state of 4-Phenyl-3H-1,3-thiazol-2-ol (enol) has been carried out. To determine lowest-energy molecular conformation of the title molecule, the selected torsion angles were varied in steps of 10° and molecular energy profile was calculated from -180° to +180°. Experimental FT-IR and FT-Raman spectra of title compound were compared with the spectral data obtained by DFT/B3LYP method. Dipole moment, polarizability, first static hyperpolarizability and molecular electrostatic potential surface map have been calculated to get a better insight of the properties of title molecule. Natural bond orbital (NBO) analysis has been done to study the stability of the molecule arising from charge delocalization. UV-Vis spectrum of the title compound was also recorded and electronic properties such as frontier orbitals and band gap energies were calculated by TD-DFT approach. To compare the drug efficacy of enolic and keto forms, QSAR properties of both forms have also been computed and discussed.

Characterization of a novel plasmid-borne thiopeptide gene cluster in Staphylococcus epidermidis strain 115

Thiopeptides are small (12- to 17-amino-acid), heavily modified peptides of bacterial origin. This antibiotic family, with more than 100 known members, is characterized by the presence of sulfur-containing heterocyclic rings and dehydrated residues within a macrocyclic peptide structure. Thiopeptides, including micrococcin P1, have garnered significant attention in recent years for their potent antimicrobial activity against bacteria, fungi, and even protozoa. Micrococcin P1 is known to target the ribosome; however, like those of other thiopeptides, its biosynthesis and mechanisms of self-immunity are poorly characterized. We have discovered an isolate of Staphylococcus epidermidis harboring the genes for thiopeptide production and self-protection on a 24-kb plasmid. Here we report the characterization of this plasmid, identify the antimicrobial peptide that it encodes, and provide evidence of a target replacement-mediated mechanism of self-immunity.

Heterologous expression of the thiopeptide antibiotic GE2270 from Planobispora rosea ATCC 53733 in Streptomyces coelicolor requires deletion of ribosomal genes from the expression construct

GE2270 is a thiopeptide antibiotic generated by extensive posttranslational modifications of a ribosomally generated precursor peptide. Thiopeptides are especially active against Gram-positive bacteria, including methicillin resistant Staphylococcus aureus (MRSA). In this study the GE2270 biosynthetic gene cluster (pbt) from Planobispora rosea ATCC 53733 was successfully expressed in the heterologous host strain Streptomyces coelicolor M1146. Notably, exconjugants containing the pbt gene cluster could only be obtained after deletion of the major part of the ribosomal genes flanking the gene cluster. This is a striking example that genes belonging to primary metabolism can prevent the successful conjugative transfer of DNA from phylogenetic distant species and thus complicate heterologous expression of secondary metabolite gene clusters. GE2270 production in the heterologous producer strain increased after introduction of the constitutive ermE* promoter upstream of the GE2270 resistance gene tuf from P. rosea. Insertion of the inducible tcp830 promoter resulted in inducible GE2270 production. When the regulatory gene pbtR was deleted, the resulting strain ceased to produce GE2270, suggesting an essential role of PbtR as a putative transcriptional activator of GE2270 expression.

Ribosomally synthesized and post-translationally modified peptide natural products: overview and recommendations for a universal nomenclature

This review presents recommended nomenclature for the biosynthesis of ribosomally synthesized and post-translationally modified peptides (RiPPs), a rapidly growing class of natural products. The current knowledge regarding the biosynthesis of the >20 distinct compound classes is also reviewed, and commonalities are discussed.

Synthesis and antimicrobial activity of amido linked pyrrolyl and pyrazolyl-oxazoles, thiazoles and imidazoles

A new class of amido linked bis heterocycles viz., pyrrolyl/pyrazolyl-oxazoles, thiazoles and imidazoles were prepared by 1,3-dipolar cycloaddition of TosMIC and diazomethane to the respective cinnamamide derivatives and screened for antimicrobial activity. The chlorosubstituted imidazolyl cinnamamide (6c) is the most potential antimicrobial agent as it displayed strong antibacterial activity against Bacillus subtilis and antifungal activity against Penicillium chrysogenum.

Thiostrepton and derivatives exhibit antimalarial and gametocytocidal activity by dually targeting parasite proteasome and apicoplast

Ribosome-targeting antibiotics exert their antimalarial activity on the apicoplast of the malaria parasite, an organelle of prokaryote origin having essential metabolic functions. These antibiotics typically cause a delayed-death phenotype, which manifests in parasite killing during the second replication cycle following administration. As an exception, treatment with the antibiotic thiostrepton results in an immediate killing. We recently demonstrated that thiostrepton and its derivatives interfere with the eukaryotic proteasome, a multimeric protease complex that is important for the degradation of ubiquitinated proteins. Here, we report that the thiostrepton-based compounds are active against chloroquine-sensitive and -resistant Plasmodium falciparum, where they rapidly eliminate parasites before DNA replication. The minor parasite fraction that escapes the fast killing of the first replication cycle is arrested in the schizont stage of the following cycle, displaying a delayed-death phenotype. Thiostrepton further exhibits gametocytocidal activity by eliminating gametocytes, the sexual precursor cells that are crucial for parasite transmission to the mosquito. Compound treatment results in an accumulation of ubiquitinated proteins in the blood stages, indicating an effect on the parasite proteasome. In accordance with these findings, expression profiling revealed that the proteasome is present in the nucleus and cytoplasm of trophozoites, schizonts, and gametocytes. In conclusion, thiostrepton derivatives represent promising candidates for malaria therapy by dually acting on two independent targets, the parasite proteasome and the apicoplast, with the capacity to eliminate both intraerythrocytic asexual and transmission stages of the parasite.

Isolation and characterization of the gene cluster for biosynthesis of the thiopeptide antibiotic TP-1161

Recently, we isolated a new thiopeptide antibiotic, TP-1161, from the fermentation broth of a marine actinomycete typed as a member of the genus Nocardiopsis. Here we report the identification, isolation, and analysis of the TP-1161 biosynthetic gene cluster from this species. The gene cluster was identified by mining a draft genome sequence using the predicted structural peptide sequence of TP-1161. Functional assignment of a ∼16-kb genomic region revealed 13 open reading frames proposed to constitute the TP-1161 biosynthetic locus. While the typical core set of thiopeptide modification enzymes contains one cyclodehydratase/dehydrogenase pair, paralogous genes predicted to encode additional cyclodehydratases and dehydrogenases were identified. Although attempts at heterologous expression of the TP-1161 gene cluster in Streptomyces coelicolor failed, its identity was confirmed through the targeted gene inactivation in the original host.

Production of a new thiopeptide antibiotic, TP-1161, by a marine Nocardiopsis species

Twenty-seven marine sediment- and sponge-derived actinomycetes with a preference for or dependence on seawater for growth were classified at the genus level using molecular taxonomy. Their potential to produce bioactive secondary metabolites was analyzed by PCR screening for genes involved in polyketide and nonribosomal peptide antibiotic synthesis. Using microwell cultures, conditions for the production of antibacterial and antifungal compounds were identified for 15 of the 27 isolates subjected to this screening. Nine of the 15 active extracts were also active against multiresistant gram-positive bacterial and/or fungal indicator organisms, including vancomycin-resistant Enterococcus faecium and multidrug-resistant Candida albicans. Activity-guided fractionation of fermentation extracts of isolate TFS65-07, showing strong antibacterial activity and classified as a Nocardiopsis species, allowed the identification and purification of the active compound. Structure elucidation revealed this compound to be a new thiopeptide antibiotic with a rare aminoacetone moiety. The in vitro antibacterial activity of this thiopeptide, designated TP-1161, against a panel of bacterial strains was determined.

The A-Z of bacterial translation inhibitors

Protein synthesis is one of the major targets in the cell for antibiotics. This review endeavors to provide a comprehensive "post-ribosome structure" A-Z of the huge diversity of antibiotics that target the bacterial translation apparatus, with an emphasis on correlating the vast wealth of biochemical data with more recently available ribosome structures, in order to understand function. The binding site, mechanism of action, and modes of resistance for 26 different classes of protein synthesis inhibitors are presented, ranging from ABT-773 to Zyvox. In addition to improving our understanding of the process of translation, insight into the mechanism of action of antibiotics is essential to the development of novel and more effective antimicrobial agents to combat emerging bacterial resistance to many clinically-relevant drugs.

Recent advances in thiopeptide antibiotic biosynthesis

Thiopeptides, or thiazolylpeptides, are a family of highly modified peptide antibiotics first discovered several decades ago. Dozens of thiopeptides have since been identified, but, until recently, the biosynthetic genes responsible for their production remained elusive. The biosynthetic systems for a handful of thiopeptide metabolites were identified in the first portion of 2009. The surprising finding that these metabolites arise from the enzymatic tailoring of a simple, linear, ribosomally-synthesized precursor peptide led to a renewed appreciation of the architectural complexity accessible by posttranslational modification. This recent progress toward understanding thiopeptide antibiotic biosynthesis benefits the discovery of novel thiopeptides by either directed screening techniques or by mining available microbial genome sequences. Furthermore, access to the biosynthetic machinery now opens an avenue to the biosynthetic engineering of thiopeptide analogs. This Highlight discusses the genetic and biochemical insights revealed by these initial reports of the biosynthetic gene clusters for thiopeptide metabolites.

Diversity of antibiotic-active bacteria associated with the brown alga Laminaria saccharina from the Baltic Sea

Bacteria associated with the marine macroalga Laminaria saccharina, collected from the Kiel Fjord (Baltic Sea, Germany), were isolated and tested for antimicrobial activity. From a total of 210 isolates, 103 strains inhibited the growth of at least one microorganism from the test panel including Gram-negative and Gram-positive bacteria as well as a yeast. Most common profiles were the inhibition of Bacillus subtilis only (30%), B. subtilis and Staphylococcus lentus (25%), and B. subtilis, S. lentus, and Candida albicans (11%). In summary, the antibiotic-active isolates covered 15 different activity patterns suggesting various modes of action. On the basis of 16S rRNA gene sequence similarities >99%, 45 phylotypes were defined, which were classified into 21 genera belonging to Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria. Phylogenetic analysis of 16S rRNA gene sequences revealed that four isolates possibly represent novel species or even genera. In conclusion, L. saccharina represents a promising source for the isolation of new bacterial taxa and antimicrobially active bacteria.

Anti-Toxoplasma gondii activity of GAS in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

The sarcotesta of Ginkgo biloba is a Chinese herbal medicine used for treating toxoplasmosis, a serious disease requiring treatment with antibiotics that can have serious side effects.

AIM OF THE STUDY

To investigate the anti-Toxoplasmagondii activity of ginkgolic acids (GAs) isolated from the Ginkgo biloba sarcotesta in Toxoplasmagondii-infected human foreskin fibroblast (HFF) cells in vitro.

MATERIALS AND METHODS

The safe concentration of GAs for HFF cells was determined by methyl thiazolyl tetrazolium (MTT) cell proliferation assay. The presence of Toxoplasmagondii was measured by [3H]-thymine deoxyriboside ([3H]-TdR) and [3H]-leucine ([3H]-Leu) incorporation, as well as Giemsa staining. The positive control was the commonly used and highly effective antibiotic azithromycin.

RESULTS

Light microscopy revealed that most HFF cells were infected after 4h of exposure to Toxoplasmagondii. After 48 h of exposure to either GAs or azithromycin, Toxoplasmagondii DNA and protein synthesis were minimal, there were no visible parasites in HFF cells, and the HFF cells had no significant morphological changes.

CONCLUSIONS

These results demonstrate that GAs have significant anti-Toxoplasma activity with low toxicity to HFF cells, suggesting that GAs could be an alternative treatment for toxoplasmosis.

Apicoplast translation, transcription and genome replication: targets for antimalarial antibiotics

Several antibiotics possess antimalarial properties, although the mechanisms by which they kill malaria parasites have been poorly understood. Recent data suggest that the target for multiple antimalarial antibiotics is the apicoplast, a chloroplast-like organelle of uncertain function. Translation inhibitors (such as tetracyclines, clindamycin and macrolides) and gyrase inhibitors (such as ciprofloxacin) cause modest antimalarial effects initially but are much more potent against the progeny of treated parasites. These progeny inherit nonfunctional apicoplasts, suggesting that blocking production of apicoplast proteins causes the 'delayed-death effect'. Interestingly, the antibiotics thiostrepton and rifampin are fast acting and might target additional processes outside the apicoplast.