Molecular mechanism of statin-mediated LOX-1 inhibition

Statins are largely used in clinics in the treatment of patients with cardiovascular diseases for their effect on lowering circulating cholesterol. Lectin-like oxidized low-density lipoprotein (LOX-1), the primary receptor for ox-LDL, plays a central role in the pathogenesis of atherosclerosis and cardiovascular disorders. We have recently shown that chronic exposure of cells to lovastatin disrupts LOX-1 receptor cluster distribution in plasma membranes, leading to a marked loss of LOX-1 function. Here we investigated the molecular mechanism of statin-mediated LOX-1 inhibition and we demonstrate that all tested statins are able to displace the binding of fluorescent ox-LDL to LOX-1 by a direct interaction with LOX-1 receptors in a cell-based binding assay. Molecular docking simulations confirm the interaction and indicate that statins completely fill the hydrophobic tunnel that crosses the C-type lectin-like (CTLD) recognition domain of LOX-1. Classical molecular dynamics simulation technique applied to the LOX-1 CTLD, considered in the entire receptor structure with or without a statin ligand inside the tunnel, indicates that the presence of a ligand largely increases the dimer stability. Electrophoretic separation and western blot confirm that different statins binding stabilize the dimer assembly of LOX-1 receptors in vivo. The simulative and experimental results allow us to propose a CTLD clamp motion, which enables the receptor-substrate coupling. These findings reveal a novel and significant functional effect of statins.     

Dopamine D1 receptor agonist and D2 receptor antagonist effects of the natural product (-)-stepholidine: molecular modeling and dynamics simulations

(-)-Stepholidine (SPD), an active ingredient of the Chinese herb Stephania, is the first compound found to have dual function as a dopamine receptor D1 agonist and D2 antagonist. Insights into dynamical behaviors of D1 and D2 receptors and their interaction modes with SPD are crucial in understanding the structural and functional characteristics of dopamine receptors. In this study a computational approach, integrating protein structure prediction, automated molecular docking, and molecular dynamics simulations were employed to investigate the dual action mechanism of SPD on the D1 and D2 receptors, with the eventual aim to develop new drugs for treating diseases affecting the central nervous system such as schizophrenia. The dynamics simulations revealed the surface features of the electrostatic potentials and the conformational "open-closed" process of the binding entrances of two dopamine receptors. Potential binding conformations of D1 and D2 receptors were obtained, and the D1-SPD and D2-SPD complexes were generated, which are in good agreement with most of experimental data. The D1-SPD structure shows that the K-167_EL-2-E-302_EL-3 (EL-2: extracellular loop 2; EL-3: extracellular loop 3) salt bridge plays an important role for both the conformational change of the extracellular domain and the binding of SPD. Based on our modeling and simulations, we proposed a mechanism of the dual action of SPD and a subsequent signal transduction model. Further mutagenesis and biophysical experiments are needed to test and improve our proposed dual action mechanism of SPD and signal transduction model.     

Molecular modeling and molecular dynamics simulation studies of Delta-Notch complex

Notch is a single-pass transmembrane receptor protein which is composed of a short extracellular region, a single-pass transmembrane domain and a small intracellular region. Notch ligand like Delta, member of the DSL protein family, is also single-pass transmembrane protein. It has been demonstrated that of the 36 EGF repeats of Notch, 11th and 12th are sufficient to mediate interactions with Delta. Crystal structure of mammalian Notch extracellular ligand binding domain contains 11 and 12 EGF-like repeats. Here a portion of the Delta protein of Drosophila, known to interact with Notch extracellular domain (ECD) has been modeled using homology modeling. The structure of the Delta-Notch complex was subsequently modeled by protein docking method using GRAMM. MD simulations of the modeled structures were performed. The structure for Delta-Notch complex has been proposed based on interaction energy parameter and planarity studies.     

Ligand binding to anti-cancer target CD44 investigated by molecular simulations

CD44 is a cell-surface glycoprotein and receptor for hyaluronan, one of the major components of the tumor extracellular matrix. There is evidence that the interaction between CD44 and hyaluronan promotes breast cancer metastasis. Recently, the molecule F-19848A was shown to inhibit hyaluronan binding to receptor CD44 in a cell-based assay. In this study, we investigated the mechanism and energetics of F-19848A binding to CD44 using molecular simulation. Using the molecular mechanics/Poisson Boltzmann surface area (MM-PBSA) method, we obtained the binding free energy and inhibition constant of the complex. The van der Waals (vdW) interaction and the extended portion of F-19848A play key roles in the binding affinity. We screened natural products from a traditional Chinese medicine database to search for CD44 inhibitors. From combining pharmaceutical requirements with docking and molecular dynamics simulations, we found ten compounds that are potentially better or equal to the F-19848A ligand at binding to CD44 receptor. Therefore, we have identified new candidates of CD44 inhibitors, based on molecular simulation, which may be effective small molecules for the therapy of breast cancer.     

Prediction on the binding domain between human interleukin-6 and its receptor

Based on the spatial conformations of human interleukin-6 (hIL-6) derived from nuclear magnetic resonance analysis and human interleukin-6 receptor (hIL-6R) modeled with homology modeling method using human growth hormone receptor as template, the interaction between hIL-6 and its receptor (hIL-6R) is studied with docking program according to the surface electrostatic potential analysis and spatial conformation complement. The stable region structure composed of hIL-6 and hIL-6R is obtained on the basis of molecular mechanism optimization and molecular dynamics simulation. The binding domain between hIL-6 and hIL-6R is predicted theoretically. Furthermore, the especial binding sites that influence the interaction between hIL-6 and hIL-6R are confirmed. The results lay a theoretical foundation for confirming the active regions of hIL-6 and designing novel antagonist with computer-guided techniques.     

3D modeling and characterization of the human CD115 monoclonal antibody H27K15 epitope and design of a chimeric CD115 target

The humanized monoclonal antibody H27K15 specifically targets human CD115, a type III tyrosine kinase receptor involved in multiple cancers and inflammatory diseases. Binding of H27K15 to hCD115 expressing cells inhibits the functional effect of colony-stimulating factor-1 (CSF-1), in a non-competitive manner. Both homology modeling and docking programs were used here to model the human CD115 extracellular domains, the H27K15 variable region and their interaction. The resulting predicted H27K15 epitope includes mainly the D1 domain in the N-terminal extracellular region of CD115 and some residues of the D2 domain. Sequence alignment with the non-binding murine CD115, enzyme-linked immunosorbent assay, nuclear magnetic resonance spectroscopy and affinity measurements by quartz crystal microbalance revealed critical residues of this epitope that are essential for H27K15 binding. A combination of computational simulations and biochemical experiments led to the design of a chimeric CD115 carrying the human epitope of H27K15 in a murine CD115 backbone that is able to bind both H27K15 as well as the murine ligands CSF-1 and IL-34. These results provide new possibilities to minutely study the functional effects of H27K15 in a transgenic mouse that would express this chimeric molecule.     

Insight into molecular interactions between two PB1 domains

Specific protein-protein interactions play crucial roles in the regulation of any biological process. Recently, a new protein-protein interaction domain termed PB1 (Phox and Bem1) was identified, which is conserved throughout evolution and present in diverse proteins functioning in signal transduction, cell polarity and survival. Here, we investigated the structure and molecular interactions of the PB1 heterodimer complex composed of the PB1 domains of the yeast proteins Bem1 and Cdc24. A structural model of the Cdc24 PB1 was built by homology modeling and molecular dynamics simulations, and experimentally validated by 15N nuclear Overhauser effect spectroscopy (NOESY)-heteronuclear single quantum coherence (HSQC) analysis. Residues at the interface of the complex for both proteins were identified by NMR titration experiments. A model of the heterodimer was obtained by docking of the two PB1 domains with HADDOCK, which applies ambiguous interaction restraints on residues at the interface to drive the docking procedure. The refined model was validated by site-directed mutagenesis on both Bem1 and Cdc24. Finally, the docking was repeated from the newly published NMR structure of Cdc24, allowing us to assess the performance of homology-based docking. Our results provide insight into the molecular structure of the Bem1-Cdc24 PB1-mediated heterodimer, which allowed identification of critical residues at the binding interface.     

Structural biology of human CD81, a receptor for hepatitis C virus

Human CD81, which is belonged to tetraspanin family, has been previously identified as a receptor for the hepatitis C virus envelope E 2 glycoprotein. The crystal structure of the human CD81 long extracellular domain, binding site for E 2 glycoprotein, is presented here at 1.6 A resolution. The tertiary structure of CD81-LEL, which is composed of five alpha-helices, is resemble for a mushroom-shaped molecules (stalk and head subdomains) and forms a dimer in the crystallographic asymmetric unit. The two disulfide bridges, which are conserved all the tetraspanin and are necessary for CD 81-HCV interaction, are stabilizing the conformation of the head domain. This head domain is solvent exposed surface region and is locating the amino acid residues which are essential for the E 2 binding. The hydrophobic cluster in this head domain may suggest that the presence of a docking site for a low complementary surface cavity in the partner E 2 glycoprotein. We proposed that the dimer structure may be important in the interactions of HCV E 2 glycoprotein and also the viral protein may occur in dimeric aggregation on the HCV envelope. This common structural motif of the tetraspanin provides the first insight onto the mechanism of HCV binding to human cell and may be targets for structure-based antiviral drug.     

Prediction on the binding domain between human interleukin-6 and its receptor

Based on the spatial conformations of human interleukin-6 (hlL-6) derived from nuclear magnetic resonance analysis and human interleukin-6 receptor (hlL-6R) modeled with homology modeling method using human growth hormone receptor as template, the interaction between hlL-6 and its receptor (hIL-6R) is studied with docking program according to the surface electrostatic potential analysis and spatial conformation complement. The stable region structure composed of hlL-6 and hlL-6R is obtained on the basis of molecular mechanism optimization and molecular dynamics simulation. The binding domain between hIL-6 and hIL-6R is predicted theoretically. Furthermore, the especial binding sites that influence the interaction between hlL-6 and hlL-6R are confirmed. The results lay a theoretical foundation for confirming the active regions of hlL-6 and designing novel antagonist with computer-guided techniques.     

3D modeling and characterization of the human CD115 monoclonal antibody H27K15 epitope and design of a chimeric CD115 target

The humanized monoclonal antibody H27K15 specifically targets human CD115, a type III tyrosine kinase receptor involved in multiple cancers and inflammatory diseases. Binding of H27K15 to hCD115 expressing cells inhibits the functional effect of colony-stimulating factor-1 (CSF-1), in a non-competitive manner. Both homology modeling and docking programs were used here to model the human CD115 extracellular domains, the H27K15 variable region and their interaction. The resulting predicted H27K15 epitope includes mainly the D1 domain in the N-terminal extracellular region of CD115 and some residues of the D2 domain. Sequence alignment with the non-binding murine CD115, enzyme-linked immunosorbent assay, nuclear magnetic resonance spectroscopy and affinity measurements by quartz crystal microbalance revealed critical residues of this epitope that are essential for H27K15 binding. A combination of computational simulations and biochemical experiments led to the design of a chimeric CD115 carrying the human epitope of H27K15 in a murine CD115 backbone that is able to bind both H27K15 as well as the murine ligands CSF-1 and IL-34. These results provide new possibilities to minutely study the functional effects of H27K15 in a transgenic mouse that would express this chimeric molecule.     

基于网络药理学、分子对接和实验验证探讨朱茯苓用于失眠的作用机制

为探讨朱茯苓治疗失眠的可能作用机制,通过TCMSP、BAT-MAN、TCMID和STITCH数据库以及文献挖掘筛选朱茯苓的活性成分及潜在靶点,利用TTD、OMIM、GeneCards和CTD数据库获取失眠类疾病的相关靶点,采用Cytoscape软件和String数据库构建活性成分-靶点网络和靶点蛋白相互作用网络,通过BioGPS数据库进行靶点的器官定位,基于David数据库进行GO功能和KEGG通路的富集分析,利用Autodock_vina软件进行活性成分和核心靶点的分子对接验证,最后通过免疫印迹法(Western blot)验证朱茯苓对γ-氨基丁酸(GABA)的两种受体蛋白α1亚基基因GABRA1和γ2亚基基因GABRG2的影响。最终筛选得到朱茯苓活性成分33种,潜在靶点267个,与失眠的交集靶点36个,多作用于脑、心脏等器官;分子对接结果显示GABRA1、GABRG2两个靶点能够与活性成分自发结合并借助氢键等分子间作用力形成较为稳定的构象;富集分析共获得189个GO条目和24条KEGG通路,主要涉及GABA信号通路、5-羟色胺(5-HT)信号通路等;Western blot实验证明朱茯苓能够增强小鼠脑内GABRA1和GABRG2蛋白的表达。通过网络药理学、分子对接和Western blot实验验证,发现朱茯苓可能通过多成分、多靶点、多途径的协同作用发挥镇静安神的作用,为深入进行朱茯苓治疗失眠的作用机制研究提供新思路和新方法。     

Novel insights into the dynamics behavior of glucagon-like peptide-1 receptor with its small molecule agonists

Abstract

The glucagon-like peptide-1 receptor (GLP-1R) is a well-known target of therapeutics industries for the treatment of various metabolic diseases like type 2 diabetes and obesity. The structural–functional relationships of small molecule agonists and GLP-1R are yet to be understood. Therefore, an attempt was made on structurally known GLP-1R agonists (Compound 1, Compound 2, Compound A, Compound B, and (S)-8) to study their interaction with the extracellular domain of GLP-1R. In this study, we explored the dynamics, intrinsic stability, and binding mechanisms of these molecules through computational modeling, docking, molecular dynamics (MD) simulations and molecular mechanics Poisson–Boltzmann surface area (MM/PBSA) binding free energy estimation. Molecular docking study depicted that hydrophobic interaction (pi–pi stacking) plays a crucial role in maintaining the stability of the complex, which was also supported by intermolecular analysis from MD simulation study. Principal component analysis suggested that the terminal ends along with the turns/loops connecting adjacent helix and strands exhibit a comparatively higher movement of main chain atoms in most of the complexes. MM/PBSA binding free energy study revealed that non-polar solvation (van der Waals and electrostatic) energy subsidizes significantly to the total binding energy, and the polar solvation energy opposes the binding agonists to GLP-1R. Overall, we provide structural features information about GLP-1R complexes that would be conducive for the discovery of new GLP-1R agonists in the future for the treatment of various metabolic diseases.

Communicated by Ramaswamy H. Sarma     

Quenching of fluorescence by meclizine,a probe study for structural and conformational changes in human serum albumin

The goal of this study was to investigate the interactions between meclizine (MEC) and human serum albumin (HSA) under physiological conditions by different spectroscopies and molecular modeling technique. The drug, MEC quenched the intrinsic fluorescence of HSA and the analysis of the results revealed that static quenching mechanism. The binding of MEC quenches the HSA fluorescence; stoichiometry was 1:1 interaction. Thermodynamic quantities were calculated at different temperatures suggested that hydrophobic and van der Waals interaction with HSA–MEC. The molecular distance, r, between donor and acceptor was estimated according to Forster’s theory of non-radiation energy transfer. CD and FT-IR studies confirm changes of secondary structure of HSA. Molecular docking studies validate MEC molecule interact to HSA in sub domain IIA.     

Direct measurements of heterotypic adhesion between the cell surface proteins CD2 and CD48

Direct force measurements were used to investigate the molecular mechanism of heterophilic adhesion between the murine T-cell adhesion glycoprotein CD2 and its ligand CD48. From the distance dependence of the protein-protein interaction potential, we demonstrate directly that the full-length extracellular domains adhere in a head-to-head orientation. The absence of long-range electrostatic protein-protein attraction further indicates that the salt bridges between the binding surfaces only influence the interaction at short range. Despite the loss of a stabilizing disulfide bond in domain 1 (D1) of CD2, adhesive failure occurs abruptly with no evidence of partial protein unfolding during detachment. Finally, these measurements between extended membrane surfaces directly confirm that the low-affinity CD2-CD48 bond generates weak adhesion and that lateral receptor mobility is required for the development of appreciable adhesion. This is the first direct measurement of the range and magnitude of the forces governing heterotypic adhesion mediated by cell surface proteins. These results both verified the head-to-head CD2-CD48 docking alignment and demonstrated the ability to elucidate the structure-function relationships of adhesion proteins from the measured distance dependence of their interaction potentials.     

Molecular recognitions in the MAP kinase cascades

The mitogen-activated protein kinase (MAPK) cascades play a pivotal role in many aspects of cellular functions, and are evolutionarily conserved from yeast to mammals. In mammals, there are four subfamily members in the MAPKs. Each MAPK has its own activators, substrates and inactivators. In order to achieve normal cellular functions, the MAPK cascades should transduce signals with high efficiency and fidelity. However, the molecular basis for the mechanism underlying the specific reactions in the MAPK cascades has not been fully understood. The MAPKs form a globular structure without a distinct domain specific for protein-protein interactions. Recent studies revealed two mechanisms regulating the signalling, the docking interaction and the scaffolding. The docking interaction is achieved through the common docking domain (the CD domain) on MAPKs, and is different from a transient enzyme-substrate interaction through the active centre of the enzymes. Almost all the MAPK-interacting molecules have a conserved motif interacting with the CD domain. The scaffolding usually utilizes a third molecule to tether several components of the MAPK cascades. Both of them are thought to regulate the enzymatic specificity and efficiency.     

Identification of invariant chain CD74 as a functional receptor of tissue inhibitor of metalloproteinases-1 (TIMP-1)

Multifunctionality of tissue inhibitor of metalloproteinases-1 (TIMP-1) comprising antiproteolytic as well as cytokinic activity has been attributed to its N-terminal and C-terminal domains, respectively. The molecular basis of the emerging proinflammatory cytokinic activity of TIMP-1 is still not completely understood. The cytokine receptor invariant chain (CD74) is involved in many inflammation-associated diseases and is highly expressed by immune cells. CD74 triggers zeta chain–associated protein kinase-70 (ZAP-70) signaling–associated activation upon interaction with its only known ligand, the macrophage migration inhibitory factor. Here, we demonstrate TIMP-1–CD74 interaction by coimmunoprecipitation and confocal microscopy in cells engineered to overexpress CD74. In silico docking in HADDOCK predicted regions of the N-terminal domain of TIMP-1 (N-TIMP-1) to interact with CD74. This was experimentally confirmed by confocal microscopy demonstrating that recombinant N-TIMP-1 lacking the entire C-terminal domain was sufficient to bind CD74. Interaction of TIMP-1 with endogenously expressed CD74 was demonstrated in the Namalwa B lymphoma cell line by dot blot binding assays as well as confocal microscopy. Functionally, we demonstrated that TIMP-1–CD74 interaction triggered intracellular ZAP-70 activation. N-TIMP-1 was sufficient to induce ZAP-70 activation and interference with the cytokine-binding site of CD74 using a synthetic peptide–abrogated TIMP-1-mediated ZAP-70 activation. Altogether, we here identified CD74 as a receptor and mediator of cytokinic TIMP-1 activity and revealed TIMP-1 as moonlighting protein harboring both cytokinic and antiproteolytic activity within its N-terminal domain. Recognition of this functional TIMP-1–CD74 interaction may shed new light on clinical attempts to therapeutically target ligand-induced CD74 activity in cancer and other inflammatory diseases.     

Molecular modeling of the three-dimensional structure of GLP-1R and its interactions with several agonists

Glucagon-like peptide-1 receptor (GLP-1R) is a promising molecular target for developing drugs treating type 2 diabetes. We have predicted the complete three-dimensional structure of GLP-1R and the binding modes of several GLP-1R agonists, including GLP-1, Boc5, and Cpd1, through a combination of homology modeling, molecular docking, and long-time molecular dynamics simulation on a lipid bilayer. Our model can reasonably interpret the results of a number of mutation experiments regarding GLP-1R as well as the successful modification to GLP-1 by Liraglutide. Our model is also validated by a recently revealed crystal structure of the extracellular domain of GLP-1R. An activation mechanism of GLP-1R agonists is proposed based on the principal component analysis and normal mode analysis on our predicted GLP-1R structure. Before the complete structure of GLP-1R is determined through experimental means, our model may serve as a valuable reference for characterizing the interactions between GLP-1R and its agonists. Figure Comparison of our predicted model of rGLP-1R (left) with the recently revealed crystal structure of hGLP-1R (right)     

Structure prediction of GPCRs using piecewise homologs and application to the human CCR5 chemokine receptor: validation through agonist and antagonist docking

This article describes the construction and validation of a three-dimensional model of the human CC chemokine receptor 5 (CCR5) receptor using multiple homology modeling. A new methodology is presented where we built each secondary structural model of the protein separately from distantly related homologs of known structure. The reliability of our approach for G-protein coupled receptors was assessed through the building of the human C-X-C chemokine receptor type 4 (CXCR4) receptor of known crystal structure. The models are refined using molecular dynamics simulations and energy minimizations using CHARMM, a classical force field for proteins. Finally, docking models of both the natural agonists and the antagonists of the receptors CCR5 and CXCR4 are proposed. This study explores the possible binding process of ligands to the receptor cavity of chemokine receptors at molecular and atomic levels. We proposed few crucial residues in receptors binding to agonist/antagonist for further validation through experimental analysis. In particular, our study provides better understanding of the blockage mechanism of the chemokine receptors CCR5 and CXCR4, and may help the identification of new lead compounds for drug development in HIV infection, inflammatory diseases, and cancer metastasis.     

Conformational and molecular interaction studies of glucagon-like peptide-2 with its N-terminal extracellular receptor domain

Glucagon-like peptide-2 (GLP-2) is a therapeutic target used in the treatment of short bowel syndrome. In this paper, we present the three dimensional solution structure of GLP-2 peptide determined using nuclear magnetic resonance (NMR) and molecular modelling. The GLP-2 adopts an α-helical conformation similar to that of secretin family of hormones. In order to understand the molecular details governing the ligand binding and receptor activation, macromolecular docking studies were performed between the N-terminal extracellular domain of GLP-2 receptor and the GLP-2 hormone using a data driven docking program.     

Molecular docking study of the interactions between the thioesterase domain of human fatty acid synthase and its ligands

Human fatty acid synthase (hFAS) thioesterase domain (TE) is an attractive drug target to treat obesity and cancer. On the basis of the recently published crystal structure of TE domain of hFAS, we performed molecular surface analysis and docking study to characterize the molecular interactions between the enzyme and its various ligands. Surface analysis identified the ligand-binding pocket of TE domain that encompasses the catalytic triad of Ser2308, His2481, Asp2338. Docking of palmitate, the main biological product of hFAS, into this pocket revealed the ligand-binding mode, in which the hydrophobic interactions are the dominant driving forces. The catalytic mechanism of TE domain can also be well explained based on the generated TE-palmitate complex structure. Moreover, the comparison of the binding modes of five fatty acids with chain lengths ranging from 12 to 20 carbons confirmed that the ligand binding pocket of TE domain is a decisive factor in chain length specificity. In addition, docking of two known TE inhibitors, c75 and orlistat revealed the pharmacophore of these hFAS TE inhibitors, which will prove useful in structure-based drug design against this important target.