G-protein kenetli reseptörlerin aktivasyon mekanizmalarının çok boyutlu modelleme yöntemleri ile incelenmesi

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2015Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 2015G-Protein kenetli reseptörler (GPCR) biyolojik membranlardaki sinyal iletiminde önemli bir rol oynayan membran proteinlerinin büyük bir bölümünü oluştururlar. Ticari olarak satılmakta olan ilaçların yaklaşık % 50'sinin hedef yapılarıdır. Son yıllarda moleküler biyoloji ve hesaplamalı kimya alanındaki gelişmeler yeni ilaçların daha iyi tasarımına yeni yollar açmaktadır. Moleküler biyoloji alanında GPCR'ların aktif ya da aktif olmayan haldeki kristal yapılarının bulunması, modelleme çalışmalarının daha güvenilir başlangıç yapılarıyla başlatılabilmesine olanak sağlamaktadır. Hesaplamalı kimya alanındaki yeni yöntemler ve bilgisayar teknolojisindeki hızlı ilerlemeler protein-protein ve protein-ilaç etkileşimlerinin kuantum mekanik ve istatistik mekanik olarak moleküler düzeyde çok boyutlu olarak incelenmesinde ve istenilen özellikteki ilaçların önerilmesinde önemli bir rol oynamaktadır. Bu tezde, yukarıda bahsedilen gelişmelerin ve yeni yöntemlerin ışığı altında GPCR'ların etkime mekanizmaları aydınlatılmaya çalışılarak, GPCR'ları hedef alan, yan etkileri en aza indirilmiş ya da yok edilmiş yeni ilaçların önerilmesi hedeflenmiştir. İlaç- protein etkileşimlerinin ve etkime mekanizmalarının hassas olarak ve pek çok yöntemin bir arada kullanıldığı bir yaklaşımla incelendiği bu çalışma farklı bölümlerden oluşmuşmaktadır. Özellikle GPCR ailesinden 3 farklı proteinle ( Dopamin D2, Kemokin tip 5 ve κ-opioid) bilgisayar ortamında yapılan çalışmalar 4 ayrı bölümde detaylı olarak incelenmiştir:G-Protein Coupled Receptors (GPCRs) constitute the largest class of membrane proteins involved in signal transduction across the biological membranes. They are essential targets for cell signaling and are of great commercial interest to the pharmaceutical industry. They make up ~50% of clinically marketed drugs and ~25% of top-selling drugs targeting this receptor family. Recent advances made in molecular biology and computational chemistry open new avenues in designing novel therapeutic compounds. Molecular biology has provided the crystal structures of several GPCRs in active and inactive states, which can be used as accurate templates in modeling studies. Computational chemistry offers a range of simulation, multi-scale modeling and virtual screening tools for definition and analysis of protein-ligand, protein-protein interactions. Development of new techniques on statistical methods and free energy simulations helps to predict novel optimal ligands. In this thesis, our aim is to use all these advances by developing an integrated approach for better understanding of activation mechanisms of GPCRs, which will help to rationalize the ligand screening process and facilitate design of new therapeutic compounds for these targets. Defining the activation mechanisms and atomistic determinants of ligand binding to GPCR targets would allow greater safety in human life. The thesis includes four chapters in which various binding interaction mechanisms based on solved and unsolved GPCR crystal structures are studied in detail. Specifically, activation mechanisms of Dopamine D2, Chemokine receptor type 5 and κ-opioid type GPCRs are elucidated using different in-silico approaches as explained below:DoktoraPh.D

Atomistic molecular dynamics simulations of typical and atypical antipsychotic drugs at the dopamine D2 receptor (D2R) elucidates their inhibition mechanism

<p>Dopamine D2 receptor (D2R) plays a pivotal role in nervous systems. Its dysfunction leads to the schizophrenia, Parkinson’s diseases and drug addiction. Since the crystal structure of the D2R was not solved yet, discovering of potent and highly selective anti-psychotic drugs carry challenges for different neurodegenerative diseases. In the current study, we modeled the three-dimensional (3D) structure of the D2R based on a recently crystallized structure of the dopamine D3 receptor. These two receptors share a high amino acid sequence homology (>70%). The interaction of the modeled receptor with well-known atypical and typical anti-psychotic drugs and the inhibition mechanisms of drugs at the catalytic domain were studied via atomistic molecular dynamics simulations. Our results revealed that, class-I and class-II forms of atypical and typical D2R antagonists follow different pathways in the inhibition of the D2Rs.</p

Discovery of Klotho peptide antagonists against Wnt3 and Wnt3a target proteins using combination of protein engineering, protein–protein docking, peptide docking and molecular dynamics simulations

The Klotho is known as lifespan enhancing protein involved in antagonizing the effect of Wnt proteins. Wnt proteins are stem cell regulators, and uninterrupted exposure of Wnt proteins to the cell can cause stem and progenitor cell senescence, which may lead to aging. Keeping in mind the importance of Klotho in Wnt signaling, in silico approaches have been applied to study the important interactions between Klotho and Wnt3 and Wnt3a (wingless-type mouse mammary tumor virus (MMTV) integration site family members 3 and 3a). The main aim of the study is to identify important residues of the Klotho that help in designing peptides which can act as Wnt antagonists. For this aim, a protein engineering study is performed for Klotho, Wnt3 and Wnt3a. During the theoretical analysis of homology models, unexpected role of number of disulfide bonds and secondary structure elements has been witnessed in case of Wnt3 and Wnt3a proteins. Different in silico experiments were carried out to observe the effect of correct number of disulfide bonds on 3D protein models. For this aim, total of 10 molecular dynamics (MD) simulations were carried out for each system. Based on the protein–protein docking simulations of selected protein models of Klotho with Wnt3 and Wnt3a, different peptides derived from Klotho have been designed. Wnt3 and Wnt3a proteins have three important domains: Index finger, N-terminal domain and a patch of ∼10 residues on the solvent exposed surface of palm domain. Protein–peptide docking of designed peptides of Klotho against three important domains of palmitoylated Wnt3 and Wnt3a yields encouraging results and leads better understanding of the Wnt protein inhibition by proposed Klotho peptides. Further in vitro studies can be carried out to verify effects of novel designed peptides as Wnt antagonists

7-Acetoxyhorminone from <i>Salvia multicaulis</i> Vahl. as Promising Inhibitor of 3-Hydroxy-3-methylglutaryl Coenzyme A (HMG-CoA) Reductase

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase is a key enzyme involved in cholesterol biosynthesis and one of the most important targets for the treatment of hypercholesterolemia. A limited number of studies on the HMG-CoA reductase inhibitory potential of natural products are available. Thus, in the current study, we aimed to test the HMG-CoA reductase inhibitory capacity of extracts from the roots and aerial parts of Salvia multicaulis Vahl., through activity-guided isolation. Our findings revealed that the root extract prepared with dichloromethane–acetone (1:1) showed the highest inhibition (71.97 ± 0.37%) at 100 µg/mL. The extract was then initially fractionated by column chromatography and the obtained fractions were monitored by thin layer chromatography. Fractions which were similar to each other were combined and a total of 15 fractions were obtained. Further conventional chromatographic studies were carried out on the active fractions. Based on these fractions, 10 known compounds, comprising 9 terpenes and 1 steroid derivative in total, were isolated and their structures were verified by a combination of IT-TOF-MS, and 1D and 2D NMR techniques. According to the enzyme inhibition data of the identified compounds, 7-acetoxyhorminone exerted the highest inhibition (84.15 ± 0.10%, IC50 = 63.6 ± 1.21 µg/mL). The molecular docking experiments on 7-acetoxyhorminone and horminone indicated that both compounds strongly bind to the active site of the enzyme

Virtual screening of small molecules databases for discovery of novel PARP-1 inhibitors: combination of in silico

Poly(ADP-ribose) polymerase-1 (PARP-1) enzyme has critical roles in DNA replication repair and recombination. Thus, PARP-1 inhibitors play an important role in the cancer therapy. In the current study, we have performed combination of in silico and in vitro studies in order to discover novel inhibitors against PARP-1 target. Structure-based virtual screening was carried out for an available small molecules database. A total of 257,951 ligands from Otava database were screened at the binding pocket of PARP-1 using high-throughput virtual screening techniques. Filtered structures based on predicted binding energy results were then used in more sophisticated molecular docking simulations (i.e. Glide/standard precision, Glide/XP, induced fit docking - IFD, and quantum mechanics polarized ligand docking - QPLD). Potential high binding affinity compounds that are predicted by molecular simulations were then tested by in vitro methods. Computationally proposed compounds as PARP-1 inhibitors (Otava Compound Codes: 7111620047 and 7119980926) were confirmed by in vitro studies. In vitro results showed that compounds 7111620047 and 7119980926 have IC50 values of 0.56 and 63M against PARP-1 target, respectively. The molecular mechanism analysis, free energy perturbation calculations using long multiple molecular dynamics simulations for the discovered compounds which showed high binding affinity against PARP-1 enzyme, as well as structure-based pharmacophore development (E-pharmacophore) studies were also studied

Synthesis, Anticholinesterase Activity and Molecular Modeling Studies of Novel Carvacrol Substituted Amide Derivatives

In the present study, 23 novel carvacrol derivatives involving the amide moiety as a linker between the alkyl chains and/or the heterocycle nucleus were synthesized and tested in vitro as acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitors. 2-(5-Isopropyl-2-methylphenoxy)-N-(quinolin-8-yl)acetamide (5v) revealed the highest inhibition properties against AChE and BuChE with the IC50 values of 1.93 and 0.05 µM, respectively. The blood–brain barrier (BBB) permeability of the potent inhibitor (5v) was also assessed by the widely used parallel artificial membrane permeability assay (PAMPA-BBB). The results showed that 5v is capable of crossing the BBB. Pharmacokinetic and toxicity profiles of the studied molecule predictions were investigated by MetaCore/MetaDrug comprehensive systems biology analysis suite. Bioactive conformations of the synthesized molecules, their predicted binding energies as well as structural and dynamical profiles of molecules at the binding pockets of AChE and BuChE targets were also investigated using different docking algorithms and molecular dynamics (MD) simulations. Communicated by Ramaswamy H. Sarma</p

Virtual screening of small molecules databases for discovery of novel PARP-1 inhibitors: combination of in silico and in vitro studies

Poly(ADP-ribose) polymerase-1 (PARP-1) enzyme has critical roles in DNA replication repair and recombination. Thus, PARP-1 inhibitors play an important role in the cancer therapy. In the current study, we have performed combination of in silico and in vitro studies in order to discover novel inhibitors against PARP-1 target. Structure-based virtual screening was carried out for an available small molecules database. A total of 257,951 ligands from Otava database were screened at the binding pocket of PARP-1 using high-throughput virtual screening techniques. Filtered structures based on predicted binding energy results were then used in more sophisticated molecular docking simulations (i.e. Glide/standard precision, Glide/XP, induced fit docking - IFD, and quantum mechanics polarized ligand docking - QPLD). Potential high binding affinity compounds that are predicted by molecular simulations were then tested by in vitro methods. Computationally proposed compounds as PARP-1 inhibitors (Otava Compound Codes: 7111620047 and 7119980926) were confirmed by in vitro studies. In vitro results showed that compounds 7111620047 and 7119980926 have IC50 values of 0.56 and 63M against PARP-1 target, respectively. The molecular mechanism analysis, free energy perturbation calculations using long multiple molecular dynamics simulations for the discovered compounds which showed high binding affinity against PARP-1 enzyme, as well as structure-based pharmacophore development (E-pharmacophore) studies were also studied