Accurate calculation of affinity changes to the close state of influenza A M2 transmembrane domain in response to subtle structural changes of adamantyl amines using free energy perturbation methods in different lipid bilayers.

Experimental binding free energies of 27 adamantyl amines against the influenza M2(22-46) WT tetramer, in its closed form at pH 8, were measured by ITC in DPC micelles. The measured Kd's range is ~44 while the antiviral potencies (IC50) range is ~750 with a good correlation between binding free energies computed with Kd and IC50 values (r = 0.76). We explored with MD simulations (ff19sb, CHARMM36m) the binding profile of complexes with strong, moderate and weak binders embedded in DMPC, DPPC, POPC or a viral mimetic membrane and using different experimental starting structures of M2. To predict accurately differences in binding free energy in response to subtle changes in the structure of the ligands, we performed 18 alchemical perturbative single topology FEP/MD NPT simulations (OPLS2005) using the BAR estimator (Desmond software) and 20 dual topology calculations TI/MD NVT simulations (ff19sb) using the MBAR estimator (Amber software) for adamantyl amines in complex with M2(22-46) WT in DMPC, DPPC, POPC. We observed that both methods with all lipids show a very good correlation between the experimental and calculated relative binding free energies (r = 0.77-0.87, mue = 0.36-0.92 kcal mol-1) with the highest performance achieved with TI/MBAR and lowest performance with FEP/BAR in DMPC bilayers. When antiviral potencies are used instead of the Kd values for computing the experimental binding free energies we obtained also good performance with both FEP/BAR (r = 0.83, mue = 0.75 kcal mol-1) and TI/MBAR (r = 0.69, mue = 0.77 kcal mol-1).

Hydrolytic Activity of Mitochondrial F1FO-ATP Synthase as a Target for Myocardial Ischemia-Reperfusion Injury: Discovery and In Vitro and In Vivo Evaluation of Novel Inhibitors.

F1FO-ATP synthase is the mitochondrial complex responsible for ATP production. During myocardial ischemia, it reverses its activity, hydrolyzing ATP and leading to energetic deficit and cardiac injury. We aimed to discover novel inhibitors of ATP hydrolysis, accessing the druggability of the target within ischemia(I)/reperfusion(R) injury. New molecular scaffolds were revealed using ligand-based virtual screening methods. Fifty-five compounds were tested on isolated murine heart mitochondria and H9c2 cells for their inhibitory activity. A pyrazolo[3,4-c]pyridine hit structure was identified and optimized in a hit-to-lead process synthesizing nine novel derivatives. Three derivatives significantly inhibited ATP hydrolysis in vitro, while in vivo, they reduced myocardial infarct size (IS). The novel compound 31 was the most effective in reducing IS, validating that inhibition of F1FO-ATP hydrolytic activity can serve as a target for cardioprotection during ischemia. Further examination of signaling pathways revealed that the cardioprotection mechanism is related to the increased ATP content in the ischemic myocardium and increased phosphorylation of PKA and phospholamban, leading to the reduction of apoptosis.

Structure-Based Lead Optimization of Enterovirus D68 2A Protease Inhibitors.

Enterovirus D68 (EV-D68) virus is a nonpolio enterovirus that typically causes respiratory illness and, in severe cases, can lead to paralysis and death in children. There is currently no vaccine or antiviral for EV-D68. We previously discovered the viral 2A protease (2Apro) as a viable antiviral drug target and identified telaprevir as a 2Apro inhibitor. 2Apro is a viral cysteine protease that cleaves the viral VP1-2A polyprotein junction. In this study, we report the X-ray crystal structures of EV-D68 2Apro, wild-type, and the C107A mutant and the structure-based lead optimization of telaprevir. Guided by the X-ray crystal structure, we predicted the binding pose of telaprevir in 2Apro using molecular dynamics simulations. We then utilized this model to inform structure-based optimization of the telaprevir's reactive warhead and P1-P4 substitutions. These efforts led to the discovery of 2Apro inhibitors with improved antiviral activity than telaprevir. These compounds represent promising lead compounds for further development as EV-D68 antivirals.

Uracil/H+ Symport by FurE Refines Aspects of the Rocking-bundle Mechanism of APC-type Transporters.

Transporters mediate the uptake of solutes, metabolites and drugs across the cell membrane. The eukaryotic FurE nucleobase/H+ symporter of Aspergillus nidulans has been used as a model protein to address structure-function relationships in the APC transporter superfamily, members of which are characterized by the LeuT-fold and seem to operate by the so-called 'rocking-bundle' mechanism. In this study, we reveal the binding mode, translocation and release pathway of uracil/H+ by FurE using path collective variable, funnel metadynamics and rational mutational analysis. Our study reveals a stepwise, induced-fit, mechanism of ordered sequential transport of proton and uracil, which in turn suggests that FurE, functions as a multi-step gated pore, rather than employing 'rocking' of compact domains, as often proposed for APC transporters. Finally, our work supports that specific residues of the cytoplasmic N-tail are involved in substrate translocation, in line with their essentiality for FurE function.

Synthesis and Biological Evaluation of Resveratrol Methoxy Derivatives.

Resveratrol, a naturally occurring stilbene, exhibits numerous beneficial health effects. Various studies have demonstrated its diverse biological actions, including anti-oxidant, anti-inflammatory, and anti-platelet properties, thereby supporting its potential for cardio protection, neuroprotection, and anti-cancer activity. However, a significant limitation of resveratrol is its weak bioavailability. To overcome this challenge, multiple research groups have investigated the synthesis of new resveratrol derivatives to enhance bioavailability and pharmacological activities. Nevertheless, there are limited data on the effects of resveratrol derivatives on platelet function. Therefore, the objective of this study was to synthesize resveratrol methoxy derivatives and evaluate their anti-platelet and anti-proliferative activity. Platelet-rich plasma (PRP) obtained from healthy volunteers was utilized to assess the derivatives' ability to inhibit platelet aggregation induced by platelet activating factor (PAF), adenosine diphosphate (ADP), and thrombin receptor activating peptide (TRAP). Additionally, the derivatives' anti-tumor activity was evaluated against the proliferation of PC-3 and HCT116 cells. The results revealed that some methoxy derivatives of resveratrol exhibited comparable or even superior anti-platelet activity compared to the original compound. The most potent derivative was the 4'-methoxy derivative, which demonstrated approximately 2.5 orders of magnitude higher anti-platelet activity against TRAP-induced platelet aggregation, indicating its potential as an anti-platelet agent. Concerning in silico studies, the 4'-methyl group of 4'-methoxy derivative is oriented similarly to the fluorophenyl-pyridyl group of Vorapaxar, buried in a hydrophobic cavity. In terms of their anti-tumor activity, 3-MRESV exhibited the highest potency in PC-3 cells, while 3,4'-DMRESV and TMRESV showed the greatest efficacy in HCT116 cells. In conclusion, methoxy derivatives of resveratrol possess similar or improved anti-platelet and anti-cancer effects, thereby holding potential as bioactive compounds in various pathological conditions.

Contribution of Deep Learning in the Investigation of Possible Dual LOX-3 Inhibitors/DPPH Scavengers: The Case of Recently Synthesized Compounds.

Even though non-steroidal anti-inflammatory drugs are the most effective treatment for inflammatory conditions, they have been linked to negative side effects. A promising approach to mitigating potential risks, is the development of new compounds able to combine anti-inflammatory with antioxidant activity to enhance activity and reduce toxicity. The implication of reactive oxygen species in inflammatory conditions has been extensively studied, based on the pro-inflammatory properties of generated free radicals. Drugs with dual activity (i.e., inhibiting inflammation related enzymes, e.g., LOX-3 and scavenging free radicals, e.g., DPPH) could find various therapeutic applications, such as in cardiovascular or neurodegenerating disorders. The challenge we embarked on using deep learning was the creation of appropriate classification and regression models to discriminate pharmacological activity and selectivity as well as to discover future compounds with dual activity prior to synthesis. An accurate filter algorithm was established, based on knowledge from compounds already evaluated in vitro, that can separate compounds with low, moderate or high activity. In this study, we constructed a customized highly effective one dimensional convolutional neural network (CONV1D), with accuracy scores up to 95.2%, that was able to identify dual active compounds, being LOX-3 inhibitors and DPPH scavengers, as an indication of simultaneous anti-inflammatory and antioxidant activity. Additionally, we created a highly accurate regression model that predicted the exact value of effectiveness of a set of recently synthesized compounds with anti-inflammatory activity, scoring a root mean square error value of 0.8. Eventually, we succeeded in observing the manner in which those newly synthesized compounds differentiate from each other, regarding a specific pharmacological target, using deep learning algorithms.

Development of Stilbenoid and Chalconoid Analogues as Potent Tyrosinase Modulators and Antioxidant Agents.

A number of stilbenoid and chalconoid derivatives were prepared by straightforward methods, and their ability to modulate tyrosinase activity and to scavenge free radicals were evaluated in vitro. The cell-free in vitro evaluation revealed two diarylpropanes, 24 and 25, as potent tyrosinase inhibitors, whereas diarylpropenoic acids seemed to enhance the enzymatic activity. An in silico evaluation of the binding affinity of the selected compounds with the crystal structure of tyrosinase was also conducted in order to obtain better insight into the mechanism. Representative synthetic compounds with inhibitory and activating properties were further evaluated in melanoma cell lines B16F1 and B16F10 for their ability to moderate tyrosinase activity and affect melanin production. Dihydrostilbene analogues I and II, exhibited a stronger anti-melanogenic effect than kojic acid through the inhibition of cellular tyrosinase activity and melanin formation, while diarylpropanoic acid 44 proved to be a potent melanogenic factor, inducing cellular tyrosinase activity and melanin formation. Moreover, the antioxidant evaluation disclosed two analogues (29 and 11) with significant free-radical-scavenging activity (12.4 and 20.3 µM), which were 10- and 6-fold more potent than ascorbic acid (122.1 µΜ), respectively.

Investigation of Tumor Cells and Receptor-Ligand Simulation Models for the Development of PET Imaging Probes Targeting PSMA and GRPR and a Possible Crosstalk between the Two Receptors.

Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) have both been used in nuclear medicine as targets for molecular imaging and therapy of prostate (PCa) and breast cancer (BCa). Three bioconjugate probes, the PSMA specific: [68Ga]Ga-1, ((HBED-CC)-Ahx-Lys-NH-CO-NH Glu or PSMA-11), the GRPR specific: [68Ga]Ga-2, ((HBED-CC)-4-amino-1-carboxymethyl piperidine-[D-Phe6, Sta13]BN(6-14), a bombesin (BN) analogue), and 3 (the BN analogue: 4-amino-1-carboxymethyl piperidine-[(R)-Phe6, Sta13]BN(6-14) connected with the fluorescent dye, BDP-FL), were synthesized and tested in vitro with PCa and BCa cell lines, more specifically, with PCa cells, PC-3 and LNCaP, with BCa cells, T47D, MDA-MB-231, and with the in-house created PSMA-overexpressing PC-3(PSMA), T47D(PSMA), and MDA-MB-231(PSMA). In addition, biomolecular simulations were conducted on the association of 1 and 2 with PSMA and GRPR. The PSMA overexpression resulted in an increase of cell-bound radioligand [68Ga]Ga-1 (PSMA) for PCa and BCa cells and also of [68Ga]Ga-2 (GRPR), especially in those cell lines already expressing GRPR. The results were confirmed by fluorescence-activated cell sorting with a PE-labeled PSMA-specific antibody and the fluorescence tracer 3. The docking calculations and molecular dynamics simulations showed how 1 enters the PSMA funnel region and how pharmacophore Glu-urea-Lys interacts with the arginine patch, the S1', and S1 subpockets by forming hydrogen and van der Waals bonds. The chelating moiety of 1, that is, HBED-CC, forms additional stabilizing hydrogen bonding and van der Waals interactions in the arene-binding site. Ligand 2 is diving into the GRPR transmembrane (TM) helical cavity, thereby forming hydrogen bonds through its amidated end, water-mediated hydrogen bonds, and π-π interactions. Our results provide valuable information regarding the molecular mechanisms involved in the interactions of 1 and 2 with PSMA and GRPR, which might be useful for the diagnostic imaging and therapy of PCa and BCa.

Discovery of SARS-CoV-2 Papain-like Protease Inhibitors through a Combination of High-Throughput Screening and a FlipGFP-Based Reporter Assay.

The papain-like protease (PLpro) of SARS-CoV-2 is a validated antiviral drug target. Through a fluorescence resonance energy transfer-based high-throughput screening and subsequent lead optimization, we identified several PLpro inhibitors including Jun9-72-2 and Jun9-75-4 with improved enzymatic inhibition and antiviral activity compared to GRL0617, which was reported as a SARS-CoV PLpro inhibitor. Significantly, we developed a cell-based FlipGFP assay that can be applied to predict the cellular antiviral activity of PLpro inhibitors in the BSL-2 setting. X-ray crystal structure of PLpro in complex with GRL0617 showed that binding of GRL0617 to SARS-CoV-2 induced a conformational change in the BL2 loop to a more closed conformation. Molecular dynamics simulations showed that Jun9-72-2 and Jun9-75-4 engaged in more extensive interactions than GRL0617. Overall, the PLpro inhibitors identified in this study represent promising candidates for further development as SARS-CoV-2 antivirals, and the FlipGFP-PLpro assay is a suitable surrogate for screening PLpro inhibitors in the BSL-2 setting.

Design of Multifaceted Antioxidants: Shifting towards Anti-Inflammatory and Antihyperlipidemic Activity.

Oxidative stress and inflammation are two conditions that coexist in many multifactorial diseases such as atherosclerosis and neurodegeneration. Thus, the design of multifunctional compounds that can concurrently tackle two or more therapeutic targets is an appealing approach. In this study, the basic NSAID structure was fused with the antioxidant moieties 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHB), its reduced alcohol 3,5-di-tert-butyl- 4-hydroxybenzyl alcohol (BHBA), or 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox), a hydrophilic analogue of α-tocopherol. Machine learning algorithms were utilized to validate the potential dual effect (anti-inflammatory and antioxidant) of the designed analogues. Derivatives 1-17 were synthesized by known esterification methods, with good to excellent yields, and were pharmacologically evaluated both in vitro and in vivo for their antioxidant and anti-inflammatory activity, whereas selected compounds were also tested in an in vivo hyperlipidemia protocol. Furthermore, the activity/binding affinity of the new compounds for lipoxygenase-3 (LOX-3) was studied not only in vitro but also via molecular docking simulations. Experimental results demonstrated that the antioxidant and anti-inflammatory activities of the new fused molecules were increased compared to the parent molecules, while molecular docking simulations validated the improved activity and revealed the binding mode of the most potent inhibitors. The purpose of their design was justified by providing a potentially safer and more efficient therapeutic approach for multifactorial diseases.

Ochraceopyronide, a Rare α-Pyrone-C-lyxofuranoside from a Soil-Derived Fungus Aspergillus ochraceopetaliformis.

The fungal strain was isolated from a soil sample collected in Giza province, Egypt, and was identified as Aspergillus ochraceopetaliformis based on phenotypic and genotypic data. The ethyl acetate extract of the fungal strain exhibited promising activity levels against several pathogenic test organisms and through a series of 1H NMR guided chromatographic separations, a new α-pyrone-C-lyxofuranoside (1) along with four known compounds (2-5) were isolated. The planar structure of the new metabolite was elucidated by detailed analysis of its 1D/2D NMR and HRMS/IR/UV spectroscopic data, while the relative configuration of the sugar moiety was determined by a combined study of NOESY and coupling constants data, with the aid of theoretical calculations. The structures of the known compounds-isolated for the first time from A. ochraceopetaliformis-were established by comparison of their spectroscopic data with those in the literature. All isolated fungal metabolites were evaluated for their antibacterial and antifungal activities against six Gram-positive and Gram-negative bacteria as well as against three human pathogenic fungi.

Multi-objective optimization methods in novel drug design.

Introduction: In multi-objective drug design, optimization gains importance, being upgraded to a discipline that attracts its own research. Current strategies are broadly classified into single - objective optimization (SOO) and multi-objective optimization (MOO).Areas covered: Starting with SOO and the ways used to incorporate multiple criteria into it, the present review focuses on MOO techniques, their comparison, advantages, and restrictions. Pareto analysis and the concept of dominance stand in the core of MOO. The Pareto front, Pareto ranking, and limitations of Pareto-based methods, due to high dimensions and data uncertainty, are outlined. Desirability functions and the weighted sum approaches are described as stand-alone techniques to transform the MOO problem to SOO or in combination with pareto analysis and evolutionary algorithms. Representative applications in different drug research areas are also discussed.Expert opinion: Despite their limitations, the use of combined MOO techniques, as well as being complementary to SOO or in conjunction with artificial intelligence, contributes dramatically to efficient drug design, assisting decisions and increasing success probabilities. For multi-target drug design, optimization is supported by network approaches, while applicability of MOO to other fields like drug technology or biological complexity opens new perspectives in the interrelated fields of medicinal chemistry and molecular biology.

Design, synthesis, and biological evaluation of new raloxifene analogues of improved antagonist activity and endometrial safety.

Raloxifene agonism of estrogen receptor (ER) in post-menopausal endometrium is not negligible. Based on a rational drug design workflow, we synthesized 14 analogues of raloxifene bearing a polar group in the aromatic ring of the basic side chain (BSC) and/or changes in the bulkiness of the BSC amino group. Analogues with a polar BSC aromatic ring and amino group substituents of increasing volume displayed increasing ER antagonism in Ishikawa cells. Analogues with cyclohexylaminoethoxy (13a) or adamantylaminoethoxy BSC (13b) lacking a polar aromatic ring displayed high ER-binding affinity and ER antagonism in Ishikawa cells higher than raloxifene and similar to fulvestrant (ICI182,780). The endometrial surface epithelium of immature female CD1 mice injected with 13b was comparable to that of vehicle-treated mice, while that of mice treated with estradiol, raloxifene or 13b in combination with estradiol was hyperplastic. These findings indicate that raloxifene analogues with a bulky BSC amino group could provide for higher endometrial safety treatment of the menopausal syndrome.

Adiponectin Signaling and Impaired GTPase Rab5 Expression in Adipocytes of Adolescents with Obesity.

INTRODUCTION: Abnormalities in adipose tissue AdipoR1; adaptor protein, phosphotyrosine interaction, PH domain, and leucine zipper containing 1 (APPL1); GTPase Rab5; adiponectin; leptin; and visfatin in adults with obesity have been associated with metabolic disturbances. OBJECTIVE: The objective of this study was to examine whether pediatric obesity disrupts elements of the adiponectin signaling pathway and GTPase Rab5 in adipose tissue. METHODS: Primary adipocyte cultures of subcutaneous abdominal tissue were obtained from 96 lean and 66 children and adolescents with obesity (AO). AdipoR1, APPL1, and GTPase Rab5 mRNA levels were measured by RT-PCR and their protein content by Western immunoblotting. Serum total and high-molecular-weight adiponectin, leptin, leptin soluble receptor (sOB-R), and visfatin were measured by ELISA. RESULTS: The mRNA expression and protein content of AdipoR1 and APPL1 did not differ significantly with obesity, age, or puberty. However, GTPase Rab5 protein was increased in the adipocytes of younger prepubertal children with obesity but decreased in AO. Leptin was increased in AO compared to lean adolescents (AL) and in older prepubertal lean (OPL) children and AL compared to younger prepubertal lean and obese children. sOB-R was higher in OPL children and in the AL and AO. Serum visfatin was increased in the younger prepubertal children and AO. CONCLUSIONS: In contrast to adults, obesity did not change the expression of AdipoR1 and APPL1 in cultured adipocytes from biopsies of subcutaneous abdominal adipose tissue of children and adolescents. Similar to adipose tissue studies in adults with obesity and metabolic dysfunction, the AO in our study showed reduced adipocyte GTPase Rab5 expression.

Investigation of the Drug Resistance Mechanism of M2-S31N Channel Blockers through Biomolecular Simulations and Viral Passage Experiments.

Recent efforts in drug development against influenza A virus (IAV) M2 proton channel S31N mutant resulted in conjugates of amantadine linked with aryl head heterocycles. To understand the mechanism of drug resistance, we chose a representative M2-S31N inhibitor, compound 3, as a chemical probe to identify resistant mutants. To increase the possibility of identifying novel resistant mutants, serial viral passage experiments were performed with multiple strains of H1N1 and H3N2 viruses in different cell lines. This approach not only identified M2 mutations around the drug-binding site, including the pore-lining residues (V27A, V27F, N31S, and G34E) and an interhelical residue (I32N), but also a new allosteric mutation (R45H), in addition to L46P previously identified, located at the C-terminus of M2 that is more than 10 Å away from the drug-binding site. The effects of each mutation were next investigated using electrophysiology, recombinant viruses, and molecular dynamics (MD) simulations. The reduced sensitivity in channel blockage correlated with increased drug resistance in antiviral assays using recombinant viruses. The MD simulations show that the V27A, V27F, G34E, and R45H mutations increase the diameter and hydration state of the pore in complex with compound 3. The Molecular Mechanics Generalized Born (MM-GBSA) calculations result in more positive binding free energies for the complexes of resistant M2 (V27A, V27F, G34E, R45H) with compound 3 compared to the stable complexes (S31N and I32N). Overall, this is the first systematic study of the drug resistance mechanism of M2-S31N channel blockers using multiple viruses in different cell lines.

Biological Evaluation and In Silico Study of Benzoic Acid Derivatives from Bjerkandera adusta Targeting Proteostasis Network Modules.

Abstract: A main cellular functional module that becomes dysfunctional during aging is the proteostasis network. In the present study, we show that benzoic acid derivatives isolated from Bjerkandera adusta promote the activity of the two main protein degradation systems, namely the ubiquitin-proteasome (UPP) and especially the autophagy-lysosome pathway (ALP) in human foreskin fibroblasts. Our findings were further supported by in silico studies, where all compounds were found to be putative binders of both cathepsins B and L. Among them, compound 3 (3-chloro-4-methoxybenzoic acid) showed the most potent interaction with both enzymes, which justifies the strong activation of cathepsins B and L (467.3 ± 3.9%) on cell-based assays. Considering that the activity of both the UPP and ALP pathways decreases with aging, our results suggest that the hydroxybenzoic acid scaffold could be considered as a promising candidate for the development of novel modulators of the proteostasis network, and likely of anti-aging agents.

X-ray Crystal Structures of the Influenza M2 Proton Channel Drug-Resistant V27A Mutant Bound to a Spiro-Adamantyl Amine Inhibitor Reveal the Mechanism of Adamantane Resistance.

The V27A mutation confers adamantane resistance on the influenza A matrix 2 (M2) proton channel and is becoming more prevalent in circulating populations of influenza A virus. We have used X-ray crystallography to determine structures of a spiro-adamantyl amine inhibitor bound to M2(22-46) V27A and also to M2(21-61) V27A in the Inwardclosed conformation. The spiro-adamantyl amine binding site is nearly identical for the two crystal structures. Compared to the M2 "wild type" (WT) with valine at position 27, we observe that the channel pore is wider at its N-terminus as a result of the V27A mutation and that this removes V27 side chain hydrophobic interactions that are important for binding of amantadine and rimantadine. The spiro-adamantyl amine inhibitor blocks proton conductance in the WT and V27A mutant channels by shifting its binding site in the pore depending on which residue is present at position 27. Additionally, in the structure of the M2(21-61) V27A construct, the C-terminus of the channel is tightly packed relative to that of the M2(22-46) construct. We observe that residues Asp44, Arg45, and Phe48 face the center of the channel pore and would be well-positioned to interact with protons exiting the M2 channel after passing through the His37 gate. A 300 ns molecular dynamics simulation of the M2(22-46) V27A-spiro-adamantyl amine complex predicts with accuracy the position of the ligands and waters inside the pore in the X-ray crystal structure of the M2(22-46) V27A complex.

Steroid sulfatase inhibiting lanostane triterpenes - Structure activity relationship and in silico insights.

Steroid sulfatase (STS) transforms hormone precursors into active steroids. Thus, it represents a target of intense research regarding hormone-dependent cancers. In this study, three ligand-based pharmacophore models were developed to identify STS inhibitors from natural sources. In a pharmacophore-based virtual screening of a curated molecular TCM database, lanostane-type triterpenes (LTTs) were predicted as STS ligands. Three traditionally used polypores rich in LTTs, i.e., Ganoderma lucidum Karst., Gloeophyllum odoratum Imazeki, and Fomitopsis pinicola Karst., were selected as starting materials. Based on eighteen thereof isolated LTTs a structure activity relationship for this compound class was established with piptolinic acid D (1), pinicolic acid B (2), and ganoderol A (3) being the most pronounced and first natural product STS inhibitors with IC50 values between 10 and 16 µM. Molecular docking studies proposed crucial ligand target interactions and a prediction tool for these natural compounds correlating with experimental findings.

Specific Residues in a Purine Transporter Are Critical for Dimerization, ER Exit, and Function.

Transporters are transmembrane proteins that mediate the selective translocation of solutes across biological membranes. Recently, we have shown that specific interactions with plasma membrane phospholipids are essential for the formation and/or stability of functional dimers of the purine transporter UapA, a prototypic eukaryotic member of the ubiquitous nucleobase ascorbate transporter (NAT) family. Here, we provide strong evidence that distinct interactions of UapA with membrane lipids are essential for ab initio formation of functional dimers in the ER, or ER exit and further subcellular trafficking. Through genetic screens, we identify mutations that restore defects in dimer formation and/or trafficking. Suppressors of defective dimerization restore ab initio formation of UapA dimers in the ER. Most of these suppressors are located in the movable core domain, but also in the core-dimerization interface and in residues of the dimerization domain exposed to lipids. Molecular dynamics suggest that the majority of suppressors stabilize interhelical interactions in the core domain and thus assist the formation of functional UapA dimers. Among suppressors restoring dimerization, a specific mutation, T401P, was also isolated independently as a suppressor restoring trafficking, suggesting that stabilization of the core domain restores function by sustaining structural defects caused by the abolishment of essential interactions with specific lipids. Importantly, the introduction of mutations topologically equivalent to T401P into a rat homolog of UapA, namely rSNBT1, permitted the functional expression of a mammalian NAT in Aspergillus nidulans Thus, our results provide a potential route for the functional expression and manipulation of mammalian transporters in the model Aspergillus system.

Cytosolic N- and C-Termini of the Aspergillus nidulans FurE Transporter Contain Distinct Elements that Regulate by Long-Range Effects Function and Specificity.

FurE, a member of the NCS1 family, is an Aspergillus nidulans transporter specific for uracil, allantoin and uric acid. Recently, we showed that C- or N-terminally truncated FurE versions are blocked for endocytosis and surprisingly show modified substrate specificities. Bifluorescence complementation assays and genetic analyses supported the idea that C- and N-termini interact dynamically and through this interaction regulate selective substrate translocation. Here we functionally dissect and define distinct motifs crucial for endocytosis, transport activity, substrate specificity and folding, in both cytosolic termini of FurE. Subsequently, we obtain novel genetic and in silico evidence indicating that the molecular dynamics of specific N- and C-terminal regions exert long-range effects on the gating mechanism responsible for substrate selection, via pH-dependent interactions with other internal cytosolic loops and membrane lipids. Our work shows that expanded cytoplasmic termini, acquired through evolution mostly in eukaryotic transporters, provide novel specific functional roles.