Homology modeling of GLUT4, an insulin regulated facilitated glucose transporter and docking studies with ATP and its inhibitors

The novel family of Warbicin® compounds inhibits glucose uptake both in yeast and human cells and restrains cancer cell proliferation

Many cancer cells share with yeast a preference for fermentation over respiration, which is associated with overactive glucose uptake and breakdown, a phenomenon called the Warburg effect in cancer cells. The yeast tps1Δ mutant shows even more pronounced hyperactive glucose uptake and phosphorylation causing glycolysis to stall at GAPDH, initiation of apoptosis through overactivation of Ras and absence of growth on glucose. The goal of the present work was to use the yeast tps1Δ strain to screen for novel compounds that would preferentially inhibit overactive glucose influx into glycolysis, while maintaining basal glucose catabolism. This is based on the assumption that the overactive glucose catabolism of the tps1Δ strain might have a similar molecular cause as the Warburg effect in cancer cells. We have isolated Warbicin ® A as a compound restoring growth on glucose of the yeast tps1Δ mutant, showed that it inhibits the proliferation of cancer cells and isolated structural analogs by screening directly for cancer cell inhibition. The Warbicin ® compounds are the first drugs that inhibit glucose uptake by both yeast Hxt and mammalian GLUT carriers. Specific concentrations did not evoke any major toxicity in mice but increase the amount of adipose tissue likely due to reduced systemic glucose uptake. Surprisingly, Warbicin ® A inhibition of yeast sugar uptake depends on sugar phosphorylation, suggesting transport-associated phosphorylation as a target. In vivo and in vitro evidence confirms physical interaction between yeast Hxt7 and hexokinase. We suggest that reversible transport-associated phosphorylation by hexokinase controls the rate of glucose uptake through hydrolysis of the inhibitory ATP molecule in the cytosolic domain of glucose carriers and that in yeast tps1Δ cells and cancer cells reversibility is compromised, causing constitutively hyperactive glucose uptake and phosphorylation. Based on their chemical structure and properties, we suggest that Warbicin ® compounds replace the inhibitory ATP molecule in the cytosolic domain of the glucose carriers, preventing hexokinase to cause hyperactive glucose uptake and catabolism.

In vitro and computational studies on the antiglycation activity of compounds isolated from antidiabetic Tetracera alnifolia stem bark

The continuous search for new compounds in natural-based plants is a promising strategy for the prevention of diseases. This work examined antiglycation activity compounds isolated from the antidiabetic extract of T. alnifolia stem bark via in vitro and computational [molecular dynamics (MD)] approach. Phytochemical investigation of ethyl acetate fraction and the application of spectroscopic methods led to the isolation and elucidation of 3 compounds: quercetin (1), kaempferol (2), and gallic acid (3). Compounds 1, 2 and 3 were then screened for antioxidant and antiglycation activities. Results show that the ethanol extract of T. alnifolia demonstrated good antioxidant activity compared to the standard gallic acid. There was a significant reduction in fasting blood glucose level progressively in diabetic rats, for 21 days compared to diabetic control. Consequently, the antiglycation activity of ethyl acetate fraction had the highest antiglycation activities, followed by dichloromethane (DCM) fraction. Compounds isolated from ethyl acetate fraction, exhibited the highest antiglycation effect for kaempferol followed by quercetin, while gallic acid had the least antiglycation effect. The root mean square of deviation (RMSD) and MM/GBSA energies obtained from molecular dynamics agree with the in vitro antiglycation activity with the sequence of structural stability in the order; kaempferol > quercetin > gallic acid. Therefore, findings from these results suggest that compounds isolated from T. alnifolia possess antiglycation activity.Communicated by Ramaswamy H. Sarma.

N6-methyladenosine Demethylase FTO Induces the Dysfunctions of Ovarian Granulosa Cells by Upregulating Flotillin 2

Polycystic ovarian syndrome (PCOS) is often accompanied by overweight/obesity and insulin resistance. The dysfunctions of ovarian granulosa cells (GCs) are closely linked with the pathogenesis of PCOS. Fat mass and obesity-associated gene (FTO), an N6-methyladenosine (m6A) demethylase, has been reported to be implicated in the risks and insulin resistance of PCOS. However, the roles of FTO in the development of GCs along with its m6A-related regulatory mechanisms are poorly defined. Cell proliferative ability was detected by MTT assay. Cell apoptotic rate was measured via flow cytometry. Insulin resistance was assessed by GLUT4 transport potential. The mRNA and protein levels of FTO and flotillin 2 (FLOT2) were determined by RT-qPCR and western blot assays, respectively. FLOT2 was screened out to be a potential FTO target through differential expression analysis for the GSE95728 dataset and target prediction analysis by POSTAR2 and STARBASE databases. The interaction between FTO and FLOT2 was analyzed by RNA immunoprecipitation (RIP) assay. The effect of FTO upregulation on FLOT2 m6A level was measured by methylated RIP (meRIP) assay. FLOT2 mRNA stability was examined by actinomycin D assay. FTO overexpression facilitated cell proliferation, hindered cell apoptosis, and induced insulin resistance in GCs. FTO promoted FLOT2 expression by reducing m6A level on FLOT2 mRNA and increasing FLOT2 mRNA stability. FLOT2 loss weakened the effects of FTO overexpression on cell proliferation/apoptosis and insulin resistance in GCs. FTO induced the dysfunctions of GCs by upregulating FLOT2, suggesting that FTO/FLOT2 might play a role in the pathophysiology of PCOS.

Methylation and Acetylation Enhanced the Antidiabetic Activity of Some Selected Flavonoids: In Vitro, Molecular Modelling and Structure Activity Relationship-Based Study

Flavonoids have been reported to exert antihyperglycemic effects and have potential to enhance the current therapy options against type 2 diabetes mellitus. However, the structure activity relationships (SAR) studies of flavonoids against this disease have not been thoroughly comprehended. Hence, in the present study, 14 structurally related flavonoids viz. wogonin, techtochrysin, norwogonin, isoscutellarein, hypolaetin, kaempferol, quercetin, methyl ether of wogonin, acetate of wogonin, acetate of norwogonin, 8-hydroxy-7-methoxyflavone, chrysin, (+)-catechin and (-)-epicatechin were taken into account for in vitro antidiabetic evaluation. Cell viability of RIN-5F pancreatic cells and 3T3-L1 pre-adipocyte cells was initially tested, then an insulin secretion assay of RIN-5F as well as adipogenesis and glucose uptake measurements of adipocyte were investigated. Subsequently, protein expressions study through adipokines measurement (leptin, adiponectin, TNF-α, RBP-4) via enzyme-linked immunosorbent assay (ELISA) kit, Western blotting analysis against GLUT4 and C/EBP-α as well as molecular docking against GLUT1 were analyzed. The results from cell culture antidiabetic assays (insulin secretion, adipogenesis, and glucose uptake), protein expressions and molecular docking pointed that the methoxy group at position C-8 is responsible for antidiabetic property of selected flavonoids via glucose uptake mechanism indicated by up regulation of GLUT4 and C/EBP-α expressions. The mechanism could be enhanced by the addition of an acetate group at C-5 and C-7 of the flavone skeleton.

Molecular aspects of glucose homeostasis in skeletal muscle--A focus on the molecular mechanisms of insulin resistance

Among all the varied actions of insulin, regulation of glucose homeostasis is the most critical and intensively studied. With the availability of glucose from nutrient metabolism, insulin action in muscle results in increased glucose disposal via uptake from the circulation and storage of excess, thereby maintaining euglycemia. This major action of insulin is executed by redistribution of the glucose transporter protein, GLUT4 from intracellular storage sites to the plasma membrane and storage of glucose in the form of glycogen which also involves modulation of actin dynamics that govern trafficking of all the signal proteins of insulin signal transduction. The cellular mechanisms responsible for these trafficking events and the defects associated with insulin resistance are largely enigmatic, and this review provides a consolidated overview of the various molecular mechanisms involved in insulin-dependent glucose homeostasis in skeletal muscle, as insulin resistance at this major peripheral site impacts whole body glucose homeostasis.

Insulin sensitization via partial agonism of PPARγ and glucose uptake through translocation and activation of GLUT4 in PI3K/p-Akt signaling pathway by embelin in type 2 diabetic rats

BACKGROUND

The present study was aimed at isolating an antidiabetic molecule from a herbal source and assessing its mechanism of action.

METHODS

Embelin, isolated from Embelia ribes Burm. (Myrsinaceae) fruit, was evaluated for its potential to regulate insulin resistance, alter β-cell dysfunction and modulate key markers involved in insulin sensitivity and glucose transport using high-fat diet (HFD) fed-streptozotocin (STZ) (40mg/kg)-induced type 2 diabetic rats. Molecular-dockings were performed to investigate the binding modes of embelin into PPARγ, PI3K, p-Akt and GLUT4 active sites.

RESULTS

Embelin (50mg/kg b wt.) reduced body weight gain, blood glucose and plasma insulin in treated diabetic rats. It further modulated the altered lipid profiles and antioxidant enzymes with cytoprotective action on β-cell. Embelin significantly increased the PPARγ expression in epididymal adipose tissue compared to diabetic control group; it also inhibited adipogenic activity; it mildly activated PPARγ levels in the liver and skeletal muscle. It also regulated insulin mediated glucose uptake in epididymal adipose tissue through translocation and activation of GLUT4 in PI3K/p-Akt signaling cascade. Embelin bound to PPARγ; it disclosed stable binding affinities to the active sites of PI3K, p-Akt and GLUT4.

CONCLUSIONS

These findings show that embelin could improve adipose tissue insulin sensitivity without increasing weight gain, enhance glycemic control, protect β-cell from damage and maintain glucose homeostasis in adipose tissue.

GENERAL SIGNIFICANCE

Embelin can be used in the prevention and treatment of type 2 diabetes mellitus caused due to obesity.

Biological evaluation and interaction of a newly designed anti-cancer Pd(II) complex and human serum albumin

The pharmacokinetics and pharmacodynamics of any drug will depend, largely, on the interaction that has with human serum albumin (HSA), the most abundant plasma protein. The interaction between newly synthesized Pd(II) complexe, 2,2'-bipyridin Butylglycinato Pd(II) nitrate, an anti-tumor component, with HSA was studied at different temperatures by fluorescence, far UV circular dichroism (CD), UV-visible spectrophotometry and theoretical approaches. The Pd(II) complex has a strong ability to quench the intrinsic fluorescence of HSA through a dynamic quenching procedure. The binding parameters and thermodynamic parameters, including δH°, δS° and δG° were calculated by fluorescence quenching method, indicated that hydrophobic forces play a major role in the interaction of Pd(II) complex with HSA. Based on Autodock, FRET (fluorescence resonance energy transfer) and fluorescence quenching data, it may be concluded that one of the binding sites in the complex of HSA is near the only one Trp of HSA (Trp214) in sub domain IIA of the protein. Far-UV-CD results indicated that Pd(II)-complex induced increase in the α-helical content of the protein. The anti-tumor property of the synthesized Pd(II) complex was studied by testing it on human tumor cell line K562. The 50% cytotoxic concentration (Cc₅₀) of complex was determined using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. Also, fluorescence staining with DAPI (4,6-diamidino-2-phenylindole) revealed some typical nuclear changes that are characteristic of apoptosis which is induced at Cc₅₀ concentration of Pd(II) complex in K562 cell line after 24 h incubation. Our results suggest that Pd(II) complex is a promising anti-proliferative agent and should execute its biological effects by inducing apoptosis.

Molecular dynamics and docking studies on cardiac troponin C

Cardiac troponin C (cTnC) is the Ca²⁺ dependent switch for contraction in heart muscle making it a potential target for drug research in the therapy of heart failure. Calcium binding on Troponin C (TnC) triggers a series of conformational changes exposing a hydrophobic pocket in the N-domain of TnC (cNTnC), which leads to force generation. Mutations and acidic pH have been related to altering the sensitivity of TnC affecting the efficiency of the heart. Bepridil, identified as a calcium sensitizer to TnC, has been experimentally found to bind to the N-domain pocket of TnC but with negative cooperativity. Screening and de novo design were carried out using LUDI and AUTOLUDI programs in this work to identify and design potential ligands that can bind to the hydrophobic pocket of TnC. Two docking centers and multiple searching radii including 5 Å, 5.5 Å, 6 Å, 6.5 Å, 7.0 Å and 7.5 Å were used in LUDI to screen the ZINC database. Based on the LUDI docking results, 8 molecules were identified from the database with good potential to bind into the binding pocket and they were used as template molecules to generate a series of new molecules by AUTOLUDI design. Out of all the newly-designed molecules, 14 new ligands were recognized to be potential ligands that can bind and fit well into the binding pocket. These molecules can be used as starting molecules to develop TnC ligands. The binding stability and binding affinity of these molecules to the protein was further analyzed by molecular dynamics simulations. The results show that the binding energies, interactions and complex stabilities of 6 ligands are comparable to or better than bepridil.

Biphasic association of T7 RNA polymerase and a nucleotide analogue, cibacron blue as a model to understand the role of initiating nucleotide in the mechanism of enzyme action

T7 RNA polymerase (T7 RNAP) is an enzyme that utilizes ribonucleotides to synthesize the nascent RNA chain in a template-dependent manner. Here we have studied the interaction of T7 RNAP with cibacron blue, an anthraquinone monochlorotriazine dye, its effect on the function of the enzyme and the probable mode of binding of the dye. We have used difference absorption spectroscopy and isothermal titration calorimetry to show that the dye binds T7 RNAP in a biphasic manner. The first phase of the binding is characterized by inactivation of the enzyme. The second binding site overlaps with the common substrate-binding site of the enzyme. We have carried out docking experiment to map the binding site of the dye in the promoter bound protein. Competitive displacement of the dye from the high affinity site by labeled GTP and isothermal titration calorimetry of high affinity GTP bound enzyme with the dye suggests a strong correlation between the high affinity dye binding and the high affinity GTP binding in T7 RNAP reported earlier from our laboratory.

In search of allosteric modulators of a7-nAChR by solvent density guided virtual screening

Nicotinic acetylcholine receptors (nAChR) are pentameric ligand gated ion channels whose activity can be modulated by endogenous neurotransmitters as well as by synthetic ligands that bind the same or distinct sites from the natural ligand. The subtype of α7 nAChR has been considered as a potenial therapeutic target for Alzheimer's disease, schizophrenia and other neurological and psychiatric disorders. Here we have developed a homology model of α7 nAChR based on two high resolution crystal structures with Brookhaven Protein Data Bank (PDB) codes 2QC1 and 2WN9 for threading on one monomer and then for building a pentamer, respectively. A number of small molecule binding sites are identified using Pocket Finder (J. An, M. Tortov, and R. Abagyan, Molecular & Cellular Proteomics, 4.6, 752-761 (2005)) of Internal Coordinate Mechanics (ICM). Remarkably, these computer-identified sites match perfectly with ordered solvent densities found in the high-resolution crystal structure of α1 nAChR, suggesting that the surface cavities in the α7 nAChR model are likely binding sites of small molecules. A high throughput virtual screening by flexible ligand docking of 5008 small molecule compounds was performed at three potential allosteric modulator (AM) binding sites of α7 nAChR using Molsoft ICM software (R. Abagyan, M. Tortov and D. Kuznetsov, J Comput Chem 15, 488-506, (1994)). Some experimentally verified allosteric modulators of α7 like CCMI comp-6, LY 7082101, 5-HI, TQS, PNU-120596, genistein, and NS-1738 ranked among top 100 compounds, while the rest of the compounds in the list could guide further search for new allosteric modulators.

Screening from the world's largest TCM database against H1N1 virus

The swine influenza virus (H1N1) 2009 pandemic highlights the importance of having effective anti-viral strategies. Recently, oseltamivir (Tamiflu) resistant influenza viruses are identified; which further emphasizes the urgency in developing new antiviral agents. In influenza virus replication cycle, viral surface glycoprotein, hemagglutinin, is responsible for viral entry into host cells. Hence, a potentially effective antiviral strategy is to inhibit viral entry mechanism. To develop novel antiviral agent that inhibits viral entry, we analyzed 20,000 traditional Chinese medicine (TCM) ingredients in hemagglutinin subtype H1 sialic acid binding site found on H1N1 virus. We then performed molecular dynamics simulations to investigate receptor-ligand interaction of the candidates obtained from docking. Here, we report three TCM derivatives that have high binding affinities to H1 sialic acid binding site residues based on structure-based calculations. The top three derivatives, xylopine_2, rosmaricine_14 and rosmaricine_15, all have an amine group that interact with Glu83 and a pyridinium group that interact with Asp103. Molecular dynamics simulations show that these derivatives form strong hydrogen bonding with Glu83 but interact transiently with Asp103. We therefore suggest that an enhanced hemagglutinin inhibitor, based on our scaffold, should be designed to bind both Glu83 and Asp103 with high affinity.

Elucidation of the glucose transport pathway in glucose transporter 4 via steered molecular dynamics simulations

BACKGROUND

GLUT4 is a predominant insulin regulated glucose transporter expressed in major glucose disposal tissues such as adipocytes and muscles. Under the unstimulated state, GLUT4 resides within intracellular vesicles. Various stimuli such as insulin translocate this protein to the plasma membrane for glucose transport. In the absence of a crystal structure for GLUT4, very little is known about the mechanism of glucose transport by this protein. Earlier we proposed a homology model for GLUT4 and performed a conventional molecular dynamics study revealing the conformational rearrangements during glucose and ATP binding. However, this study could not explain the transport of glucose through the permeation tunnel.

METHODOLOGY/PRINCIPAL FINDINGS

To elucidate the molecular mechanism of glucose transport and its energetic, a steered molecular dynamics study (SMD) was used. Glucose was pulled from the extracellular end of GLUT4 to the cytoplasm along the pathway using constant velocity pulling method. We identified several key residues within the tunnel that interact directly with either the backbone ring or the hydroxyl groups of glucose. A rotation of glucose molecule was seen near the sugar binding site facilitating the sugar recognition process at the QLS binding site.

CONCLUSIONS/SIGNIFICANCE

This study proposes a possible glucose transport pathway and aids the identification of several residues that make direct interactions with glucose during glucose transport. Mutational studies are required to further validate the observation made in this study.

The key residues of active sites on the catalytic fragment for paclitaxel interacting with poly (ADP-ribose) polymerase

Poly(ADP-ribose) polymerase (PARP) is regarded as a target protein for paclitaxel (PTX) to bind. An important issue is to identify the key residues as active sites for PTX interacting with PARP, which will help to understand the potential drug activity of PTX against cancer cells. Using docking method and MD simulation, we have constructed a refined structure of PTX docked on the catalytic function domain of PARP (PDB code: 1A26). The residues Glu327(988), Tyr246(907), Lys242(903), His165(826), Asp105(766), Gln102(763) and Gln98(759) in PARP are identified as potential sites involved in interaction with PTX according to binding energy (E(b)) between PTX and single residue calculated with B3LYP/6-31G(d,p). These residues form an active binding pocket located on the surface of the catalytic fragment, possibly interacting with the required groups of PTX leading to its activity against cancer cells. It is noted that most of the active sites make conatct with the "southern hemisphere" of PTX except for one residue, Tyr246(907), which interacts with the "northern hemisphere" of PTX. The conformation of PTX in complex with the catalytic fragment is observed as being T-shaped, similar to that complexed with β-tubulin. The total Eb of -269.9 kJ/mol represents the potent interaction between PTX and the catalytic fragment, implying that PTX can readily bind to the active pocket. The tight association of PTX with the catalytic fragment would inhibit PARP activation, suggesting a potential application of PTX as an effective antineoplastic agent.

A novel OmpY porin from Yersinia pseudotuberculosis: structure, channel-forming activity and trimer thermal stability

A novel OmpY porin was predicted based on the Yersinia pseudotuberculosis genome analysis. Whereas it has the different genomic annotation such as "outer membrane protein N" (ABS46310.1) in str. IP 31758 or "outer membrane protein C2, porin" (YP_070481.1) in str. IP32953, it might be warranted to rename the OmpN/OmpC2 to OmpY, "outer membrane protein Y", where letter "Y" pertained to Yersinia. Both phylogenetic analysis and genomic localization clearly support that the OmpY porin belongs to a new group of general bacterial porins. The recombinant OmpY protein with its signal sequence was overexpressed in porin-deficient Escherichia coli strain. The mature rOmpY was shown to insert into outer membrane as a trimer. The OmpY porin, isolated from the outer membrane, was studied employing spectroscopic, electrophoretic and bilayer lipid membranes techniques. The far UV CD spectrum of rOmpY was essentially identical to that of Y. pseudotuberculosis OmpF. The near UV CD spectrum of rOmpY was weaker and smoother than that of OmpF. The rOmpY single-channel conductance was 180 ± 20 pS in 0.1 M NaCl and was lower than that of the OmpF porin. As was shown by electrophoretic and bilayer lipid membrane experiments, the rOmpY trimers were less thermostable than the OmpF trimers. The porins differed in the trimer-monomer transition temperature by about 20°C. The three-dimensional structural models of the Y. pseudotuberculosis OmpY and OmpF trimers were generated and the intra- and intermonomeric interactions stabilizing the porins were investigated. The difference in the thermal stability of OmpY and OmpF trimers was established to correlate with the difference in intermonomeric polar contacts.

Potent inhibitor design against H1N1 swine influenza: structure-based and molecular dynamics analysis for M2 inhibitors from traditional Chinese medicine database

The rapid spread of influenza virus subtype H1N1 poses a great threat to million lives worldwide. To search for new anti-influenza compounds, we performed molecular docking and molecular dynamics simulation to identify potential traditional Chinese medicine (TCM) constituents that could block influenza M2 channel activity. Quinic acid, genipin, syringic acid, cucurbitine, fagarine, and methyl isoferulate all have extremely well docking results as compared to control amantadine. Further de novo drug design suggests that derivatives of genipin and methyl isoferulate could have enhanced binding affinity towards M2 channel. Selected molecular dynamics simulations of M2-derivative complexes show stable hydrogen bond interactions between the derivatives and M2 residues, Ser10 and Ala9. To our best knowledge, this is the first study on the anti-viral activity of the above listed TCM compounds.

SMpred: a support vector machine approach to identify structural motifs in protein structure without using evolutionary information

Knowledge of three dimensional structure is essential to understand the function of a protein. Although the overall fold is made from the whole details of its sequence, a small group of residues, often called as structural motifs, play a crucial role in determining the protein fold and its stability. Identification of such structural motifs requires sufficient number of sequence and structural homologs to define conservation and evolutionary information. Unfortunately, there are many structures in the protein structure databases have no homologous structures or sequences. In this work, we report an SVM method, SMpred, to identify structural motifs from single protein structure without using sequence and structural homologs. SMpred method was trained and tested using 132 proteins domains containing 581 motifs. SMpred method achieved 78.79% accuracy with 79.06% sensitivity and 78.53% specificity. The performance of SMpred was evaluated with MegaMotifBase using 188 proteins containing 1161 motifs. Out of 1161 motifs, SMpred correctly identified 1503 structural motifs reported in MegaMotifBase. Further, we showed that SMpred is useful approach for the length deviant superfamilies and single member superfamilies. This result suggests the usefulness of our approach for facilitating the identification of structural motifs in protein structure in the absence of sequence and structural homologs. The dataset and executable for the SMpred algorithm is available at http://www3.ntu.edu.sg/home/EPNSugan/index_files/SMpred.htm.

Anti-infectious bronchitis virus (IBV) activity of 1,8-cineole: effect on nucleocapsid (N) protein

In the present study, anti-IBV (infectious bronchitis virus) activity of 1,8-cineole was studied by MTT assay, as well as docking and molecular dynamic (MD) simulations. The CC50 of 1,8-cineole was above 10 mM. And the maximum noncytotoxic concentration (TD0) of 1,8-cineole was determined to be 3.90 ± 0.22 mM, which was much higher than that of ribavirin (0.78 ± 0.15 mM). 1,8-cineole could inhibit IBV with an IC(50) of 0.61 mM. MTT assay showed that the inhibition of IBV by 1, 8-cineole appears to occur moderately before entering the cell but much strongly after penetration of the virus into the cell. In silico simulations indicated that the binding site of 1,8-cineole was located at the N terminus of phosphorylated nucleocapsid (N) protein, with interaction energy equaling -40.33 kcal mol(-1). The residues TyrA92, ProA134, PheA137, AspA138 and TyrA140 had important roles during the binding process and are fully or partially conserved in various IBV strains. Based on spatial and energetic criteria, 1,8-cineole interfered with the binding between RNA and IBV N-protein. Results presented here may suggest that 1,8-cineole possesses anti-IBV properties, and therefore is a potential source of anti-IBV ingredients for the pharmaceutical industry.

Molecular dynamics simulation studies of GLUT4: substrate-free and substrate-induced dynamics and ATP-mediated glucose transport inhibition

Background

Glucose transporter 4 (GLUT4) is an insulin facilitated glucose transporter that plays an important role in maintaining blood glucose homeostasis. GLUT4 is sequestered into intracellular vesicles in unstimulated cells and translocated to the plasma membrane by various stimuli. Understanding the structural details of GLUT4 will provide insights into the mechanism of glucose transport and its regulation. To date, a crystal structure for GLUT4 is not available. However, earlier work from our laboratory proposed a well validated homology model for GLUT4 based on the experimental data available on GLUT1 and the crystal structure data obtained from the glycerol 3-phosphate transporter.

Methodology/Principal Findings

In the present study, the dynamic behavior of GLUT4 in a membrane environment was analyzed using three forms of GLUT4 (apo, substrate and ATP-substrate bound states). Apo form simulation analysis revealed an extracellular open conformation of GLUT4 in the membrane favoring easy exofacial binding of substrate. Simulation studies with the substrate bound form proposed a stable state of GLUT4 with glucose, which can be a substrate-occluded state of the transporter. Principal component analysis suggested a clockwise movement for the domains in the apo form, whereas ATP substrate-bound form induced an anti-clockwise rotation. Simulation studies suggested distinct conformational changes for the GLUT4 domains in the ATP substrate-bound form and favor a constricted behavior for the transport channel. Various inter-domain hydrogen bonds and switching of a salt-bridge network from E345-R350-E409 to E345-R169-E409 contributed to this ATP-mediated channel constriction favoring substrate occlusion and prevention of its release into cytoplasm. These data are consistent with the biochemical studies, suggesting an inhibitory role for ATP in GLUT-mediated glucose transport.

Conclusions/Significance

In the absence of a crystal structure for any glucose transporter, this study provides mechanistic details of the conformational changes in GLUT4 induced by substrate and its regulator.

A novel strategy for designing the selective PPAR agonist by the "sum of activity" model

Peroxisome proliferator-activated receptors alpha, delta and gamma are a collection of ligand-activated transcription factors crucial in lipid and glucose homeostasis. The involvement of these receptors in lipid metabolism makes them perfect therapeutic target for treating obesity and stroke. In this study, 'sum of activity' model was employed to design multi-target agonists. We used a new strategy to design agonists that fit both alpha and delta but not gamma, to avoid side effect. The CoMFA and CoMSIA models were used to explore the pharmacophore features by constructing three individual models: (a) alpha-model, (b) delta-model and (c) gamma-model, and two sum models: (d) alpha, delta- model, and (e) alpha, delta and gamma-model. The CoMFA model yielded a significant cross validation value, q(2), of 0.729 and non-cross validation value, r(2), of 0.933 in the alpha, delta-model. The CoMSIA studies yielded the best predictive models with q(2) of 0.622 in A+S and with r(2) of 0.911 in the alpha, delta-model. Finally, we proposed that distinct features shown in models (a), (b), (d) but not (c) and (e) should be accounted in designing weight-controlling drugs.

Virtual screening and drug design for PDE-5 receptor from traditional Chinese medicine database

Erectile dysfunction (ED) is a sexual disorder mainly caused by decrease in cellular concentration of cyclic guanosine monophosphate (cGMP), which is degraded by phosphodiesterase type-5 (PDE-5). As a potent therapeutic target, inhibitors such as Viagra , Cialis, and Levitra have already been developed to target PDE-5 for treating ED; traditional Chinese medicine, Epimedium sagittatum, also has shown prominent results as well. To developed new PDE-5 inhibitors, we performed a virtual screening of traditional Chinese medicine (TCM) database and docking analyses to identify candidates. Known PDE-5 inhibitors were used to construct a three dimensional quantitative structure-activity relationship (3D QSAR) model by HypoGen program. From docking analyses, isochlorogenic acid b was identified as the most potential inhibitory compound. De novo evolution designed 47 derivatives. Of the 47 derivatives, seven were able to map into the pharmacophore model, and these seven compounds were suggested to be the most promising leads for inhibiting PDE-5. An analysis of the hydrogen bond interactions formed between the docked ligands and PDE-5 identified ASN662, SER663 and GLN817 as the most frequently interacting residues. A total of eight novel leading compounds were identified to have favorable interaction with PDE-5. These compounds all had hydrogen bond interactions with three key residues that could be further investigated for understanding of PDE-5 and ligands interaction.

Gallic acid induces GLUT4 translocation and glucose uptake activity in 3T3-L1 cells

GLUT4, a 12 transmembrane protein, plays a major role in insulin mediated glucose transport in muscle and adipocytes. For glucose transport, the GLUT4 protein needs to be translocated to the plasma membrane from the intracellular pool and it is possible that certain compounds may be able to enhance this process. In the present work, we have shown that gallic acid can increase GLUT4 translocation and glucose uptake activity in an Akt-independent but wortmannin-sensitive manner. Further analysis suggested the role of atypical protein kinase Czeta/lambda in gallic acid mediated GLUT4 translocation and glucose uptake.