Structural basis of malaria transmission blockade by a monoclonal antibody to gamete fusogen HAP2

HAP2 is a transmembrane gamete fusogen found in multiple eukaryotic kingdoms and is structurally homologous to viral class II fusogens. Studies in Plasmodium have suggested that HAP2 is an attractive target for vaccines that block transmission of malaria. HAP2 has three extracellular domains, arranged in the order D2, D1, and D3. Here, we report monoclonal antibodies against the D3 fragment of Plasmodium berghei HAP2 and crystal structures of D3 in complex with Fab fragments of two of these antibodies, one of which blocks fertilization of Plasmodium berghei in vitro and transmission of malaria in mosquitoes. We also show how this Fab binds the complete HAP2 ectodomain with electron microscopy. The two antibodies cross-react with HAP2 among multiple plasmodial species. Our characterization of the Plasmodium D3 structure, HAP2 ectodomain architecture, and mechanism of inhibition provide insights for the development of a vaccine to block malaria transmission.

Inhibition of LPMOs by Fermented Persimmon Juice

Fermented persimmon juice, Kakishibu, has traditionally been used for wood and paper protection. This protective effect stems at least partially from inhibition of microbial cellulose degrading enzymes. The inhibitory effect of Kakishibu on lytic polysaccharide monooxygenases (LPMOs) and on a cocktail of cellulose hydrolases was studied, using three different cellulosic substrates. Dose dependent inhibition of LPMO activity by a commercial Kakishibu product was assessed for the well-characterized LPMO from Thermoascus aurantiacus TaAA9A, and the inhibitory effect was confirmed on five additional microbial LPMOs. The model tannin compound, tannic acid exhibited a similar inhibitory effect on TaAA9A as Kakishibu. It was further shown that both polyethylene glycol and tannase can alleviate the inhibitory effect of Kakishibu and tannic acid, indicating a likely mechanism of inhibition caused by unspecific tannin–protein interactions.

In vivo and in vitro prospection of the anti-ophidic properties exercised by the extracts of Jacaranda decurrens L.

The research and development of alternative treatments for snakebites (e.g., medicinal plants) is necessary due to the high costs of the existing ones. The effects of the aqueous extracts from Jacaranda decurrens leaves, roots, and xylopodium were analyzed upon the venom-induced (Bothrops spp. and Crotalus spp.) systemic and local toxicity. The extracts were able to partially inhibit the phospholipase activity of the venoms from Bothrops jararacussu and Crotalus durissus terrificus. The myotoxic, edema-inducing, coagulant, and hemorrhagic activities were also inhibited. The SDS-PAGE showed that the venom proteins were intact after their incubation with the extracts. This suggests that the possible mechanism of inhibition is not related to the degradation of the protein but rather to their binding to specific sites of the enzymes. The extracts significantly prolonged the survival time of animals in the lethality assay performed with Crotalus durissus terrificus venom and its toxin (crotoxin). The anti-ophidic activity of medicinal plants may aid in the management of snakebites in distant locations by reducing the victim’s local effects and time to heal.

Screening for Activity Against AMPA Receptors Among Anticonvulsants—Focus on Phenytoin

The interest in AMPA receptors as a target for epilepsy treatment increased substantially after the approval of perampanel, a negative AMPA receptor allosteric antagonist, for the treatment of partial-onset seizures and generalized tonic-clonic seizures. Here we performed a screening for activity against native calcium-permeable AMPA receptors (CP-AMPARs) and calcium-impermeable AMPA receptors (CI-AMPARs) among different anticonvulsants using the whole-cell patch-clamp method on isolated Wistar rat brain neurons. Lamotrigine, topiramate, levetiracetam, felbamate, carbamazepine, tiagabin, vigabatrin, zonisamide, and gabapentin in 100-µM concentration were practically inactive against both major subtypes of AMPARs, while phenytoin reversibly inhibited them with IC50 of 30 ± 4 μM and 250 ± 60 µM for CI-AMPARs and CP-AMPARs, respectively. The action of phenytoin on CI-AMPARs was attenuated in experiments with high agonist concentrations, in the presence of cyclothiazide and at pH 9.0. Features of phenytoin action matched those of the CI-AMPARs pore blocker pentobarbital, being different from classical competitive inhibitors, negative allosteric inhibitors, and CP-AMPARs selective channel blockers. Close 3D similarity between phenytoin and pentobarbital also suggests a common binding site in the pore and mechanism of inhibition. The main target for phenytoin in the brain, which is believed to underlie its anticonvulsant properties, are voltage-gated sodium channels. Here we have shown for the first time that phenytoin inhibits CI-AMPARs with similar potency. Thus, AMPAR inhibition by phenytoin may contribute to its anticonvulsant properties as well as its side effects.

In silico study of lutein as anti-HER-2 receptors in breast cancer treatment

Human Epidermal Receptor-2 (HER-2) overexpression is implicated in breast cancer progression; thus, HER-2 is widely used as the target of anticancer therapy. Lapatinib is a drug widely used to inhibit the HER-2 receptor and tyrosine kinase; however, it develops drug resistance. Lutein is promising to be developed as breast cancer therapy. This study aims to determine the mechanism of inhibition of HER-2 receptor overexpression by lutein in silico. Molecular docking was carried out by optimizing the lutein and lapatinib, preparing of protein target HER-2 (PDB ID 3PP0), validating of molecular docking protocol, and docking of lutein and lapatinib on HER-2. The study resulted in the binding energy of -12.37 kcal/mol, while the binding energy of the native ligand and lapatinib to HER-2 was -10.43 kcal/mol and -12.25 kcal/mol, respectively. The binding energy showed that lutein has potential as breast anticancer suggested from the stronger affinity to HER2.

Identifying the Mechanism of Action of Bioactive 1,2-Cyclopropyl Carbohydrates

<p>Cyclopropanes and carbohydrates have long been used in the field of drug development. Previous work has shown that 1,2-cyclopropyl carbohydrates display bioactivity in both HeLa cancer cell lines¹ and in yeast² with a tentatively proposed mechanism of inhibition occurring through an enzymatic cyclopropane ring opening reaction and subsequent formation of a covalent bond with a target enzyme.² A small library of 1,2-cyclopropyl carbohydrate derivatives were synthesised based on known pharmacophores to examine further the potential mechanism of inhibition of such compounds and confirm the occurrence of enzyme-catalysed cyclopropane ring-opening reactions. Initial synthetic efforts were focused on the synthesis of the 1,2-dichlorocyclopropyl carbohydrate 23, which, through the optimisation of an essential C-6 detritylation reaction, was achieved in moderate yields of 32% over 7 steps. Following this, the ethoxycarbonyl substituted 1,2-cyclopropyl carbohydrate 54 was synthesised over 7 steps in a 22% yield through a rhodium acetate-catalysed addition of ethyl diazoacetate (49) to the glucal substrate 40. It was envisioned that if enzymatic cyclopropane ring-opening was occurring to form a C-7 carbanion, this would in turn be stabilised through the potential enolate formation of 54. Use of N,N-ditosylhydrazine in the synthesis of propargyl diazoacetate (58) followed by a rhodium acetate-catalysed cyclopropanation of 58 with substrate 40 resulted in the successful synthesis of 61 over 7 steps in a total yield of 9%. The incorporation of the propargyl substituent in 61 was introduced as a molecular probe in an attempt to isolate the target protein through an affinity purification procedure. The bioactivity of the propargyl derivative 61 was consistent with the synthesised compounds 23 and 54. It was proposed that these compounds undergo an enzymatic cyclopropane ring opening reaction accompanied with a clear diastereoselective preference for the α-stereoisomer of the cyclopropane ring, consistent with a target-based activation of the compounds. Chemical genetic analysis of the resulting bioactive compounds was undertaken using a deletion mutant array of Saccharomyces cerevisiae to elucidate a potential mechanism of action. Analysis of the results showed that, of the 4800 homozygous deletion strains tested in the high-throughput screens, a total of 122 strains were found following validation to sensitise and 68 to give resistance against 23 and 54. These sensitive and resistant mutants were subjected to a validation assay. Following validation, genes whose deletion led to sensitivity or resistance were then subjected to gene ontology term enrichment analysis which showed enrichment in the cytosolic ribosome, SNARE complex and SNAP receptor activity for resistant strains and enrichment in endoplasmic reticulum and endomembrane systems was found for the sensitive strain. Genes whose deletion sensitised to both compounds showed strong enrichment in cellular protein localisation, intra-golgi vesicale-mediated transport and the endomembrane system. Target identification and isolation were attempted through an affinity purification procedure using compound 61 and an azide-modified agarose resin. However, this was without success, either through inaccessibility of the alkyne of the target probe or because the target resides in the membrane-associated fraction which was discarded prior to treatment with the probe. This study suggests that the 1,2-cyclopropyl carbohydrates synthesised function through a cyclopropane ring-opening reaction, assisted by an enzymatic nucleophile. Chemical genetic analysis showed that the target of these compounds is involved in protein transport and protein localisation most likely relating to the vesicle tethering. Although many aspects of this work still need further investigation, either through the synthesis of new 1,2-cyclopropyl carbohydrates to increase bioactivity and better understand the enzymatic target, or through further biological procedures to better understand the mechanism of action, the use of 1,2-cyclopropyl carbohydrates as a potential pharmaceuticals or probes of protein trafficking shows much promise.</p>

Sulfate adenylyl transferase kinetics and mechanisms of metabolic inhibitors of microbial sulfate respiration

Sulfate analog oxyanions that function as selective metabolic inhibitors of dissimilatory sulfate reducing microorganisms (SRM) are widely used in ecological studies and industrial applications. As such, it is important to understand the mode of action and mechanisms of tolerance or adaptation to these compounds. Different oxyanions vary widely in their inhibitory potency and mechanism of inhibition, but current evidence suggests that the sulfate adenylyl transferase/ATP sulfurylase (Sat) enzyme is an important target. We heterologously expressed and purified the Sat from the model SRM, Desulfovibrio alaskensis G20. With this enzyme we determined the turnover kinetics (kcat, KM) for alternative substrates (molybdate, selenate, arsenate, monofluorophosphate, and chromate) and inhibition constants (KI) for competitive inhibitors (perchlorate, chlorate, and nitrate). These measurements enable the first quantitative comparisons of these compounds as substrates or inhibitors of a purified Sat from a respiratory sulfate reducer. We compare predicted half-maximal inhibitory concentrations (IC50) based on Sat kinetics with measured IC50 values against D. alaskensis G20 growth and discuss our results in light of known mechanisms of sensitivity or resistance to oxyanions. This analysis helps with the interpretation of recent adaptive laboratory evolution studies and illustrates the value of interpreting gene–microbe–environment interactions through the lens of enzyme kinetics.

Structural basis of main proteases of coronavirus bound to drug candidate PF-07321332

The high mutation rate of COVID-19 and the prevalence of multiple variants strongly support the need for pharmacological options to complement vaccine strategies. One region that appears highly conserved among different genus of coronaviruses is the substrate binding site of the main protease (Mpro or 3CLpro), making it an attractive target for the development of broad-spectrum drugs for multiple coronaviruses. PF-07321332 developed by Pfizer is the first orally administered inhibitor targeting the main protease of SARS-CoV-2, which also has shown potency against other coronaviruses. Here we report three crystal structures of main protease of SARS-CoV-2, SARS-CoV and MERS-CoV bound to the inhibitor PF-07321332. The structures reveal a ligand-binding site that is conserved among SARS-CoV-2, SARS-CoV and MERS-CoV, providing insights into the mechanism of inhibition of viral replication. The long and narrow cavity in the cleft between domains I and II of main protease harbors multiple inhibitor binding sites, where PF-07321332 occupies subsites S1, S2 and S4 and appears more restricted compared with other inhibitors. A detailed analysis of these structures illuminated key structural determinants essential for inhibition and elucidated the binding mode of action of main proteases from different coronaviruses. Given the importance of main protease for the treatment of SARS-CoV-2 infection, insights derived from this study should accelerate the design of safer and more effective antivirals.