Molecular modeling studies on HIV-1 Reverse Transcriptase (RT) and Heat shock protein (Hsp) 90 as a potential anti-HIV-1 target.

Masters Degree. University of KwaZulu-Natal, Durban.Human immunodeficiency virus (HIV) infection is the leading cause of death globally. This dissertation addresses two HIV-1 target proteins namely, HIV-1 Reverse Transcriptase (RT) and Heat shock protein (Hsp) 90. More specifically for HIV-1 RT, a case study for the identification of potential inhibitors as anti-HIV agents was carried out. A more refined virtual screening (VS) approach was implemented, which was an improvement on work previously published by our group- “target-bound pharmacophore modeling approach”. This study generated a pharmacophore library based only on highly contributing amino acid residues (HCAAR), instead of arbitrary pharmacophores, most commonly used in the conventional approaches in literature. HCAAR were distinguished based on free binding energy (FBE) contributions, obtained using calculation from molecular dynamics (MD) simulations. Previous approaches have relied on the docking score (DS) to generate energy-based pharmacophore models. However, DS are reportedly unreliable. Thus we present a model for a per-residue energy decomposition (PRED), constructed from MD simulation ensembles generating a more trustworthy pharmacophore model which can be applied in drug discovery workflow. This approach was employed in screening for potential HIV-1 RT inhibitors using the pharmacophoric features of the compound GSK952. The complex was subjected to docking and thereafter MD simulations confirmed the stability of the system. Experimentally determined inhibitors with known HIV-RT inhibitory activity were used to validate the proposed protocol. Two potential hits ZINC46849657 and ZINC54359621 showed a significant potential with regards to FBE. Reported results obtained from this work confirm that this new approach is favourable to the future of drug design process. Hsp90 was recently discovered to play a vital role in HIV-1 replication. Thus has emerged, as a promising target for anti-HIV-1 drugs. The molecular mechanism of Hsp90 is poorly understood, thus the second study was aimed to address this issue and provide a clear insight to the inhibition mechanism of Hsp90. Reasonable continuous MD simulations were employed for both unbound and bound Hsp90 conformations, to understand the dimerization and inhibition mechanisms. Results demonstrated that coumermycin A1 (C-A1), a newly discovered Hsp90 inhibitor, binds at the CTD dimer of Hsp90 and lead to a significant separation between orthogonally opposed residues, such as Arg591.B, Lys594.A, Ser663.A, Thr653.B, Ala665.A, Thr649.B, Leu646.B and Asn669A. A Large difference in magnitudes was observed in the radius of gyration (Rg), per-residue fluctuation, root-mean-square deviation (RMSD) and root-mean-square fluctuation (RMSF) confirming a completely more flexible state for the unbound conformation associated with dimerization. Whereas, a less globally correlated motion in the case of the bound conformer of Hsp90 approved a reduction of the dimeric process. This undoubtedly underlines the inhibition process due to ligand binding. The detailed dynamic analyses of Hsp90 presented herein are believed to give a greater insight and understanding to the function and mechanisms of inhibition of Hsp90. The report on the inhibitor-binding mode would also be of great assistance in the design of prospective inhibitors against Hsp90 as potential HIV target

Probing Retroviral and Retrotransposon Genome Structures: The “SHAPE” of Things to Come

Understanding the nuances of RNA structure as they pertain to biological function remains a formidable challenge for retrovirus research and development of RNA-based therapeutics, an area of particular importance with respect to combating HIV infection. Although a variety of chemical and enzymatic RNA probing techniques have been successfully employed for more than 30 years, they primarily interrogate small (100–500 nt) RNAs that have been removed from their biological context, potentially eliminating long-range tertiary interactions (such as kissing loops and pseudoknots) that may play a critical regulatory role. Selective 2′ hydroxyl acylation analyzed by primer extension (SHAPE), pioneered recently by Merino and colleagues, represents a facile, user-friendly technology capable of interrogating RNA structure with a single reagent and, combined with automated capillary electrophoresis, can analyze an entire 10,000-nucleotide RNA genome in a matter of weeks. Despite these obvious advantages, SHAPE essentially provides a nucleotide “connectivity map,” conversion of which into a 3-D structure requires a variety of complementary approaches. This paper summarizes contributions from SHAPE towards our understanding of the structure of retroviral genomes, modifications to which technology that have been developed to address some of its limitations, and future challenges

Ribozymes: the characteristics and properties of catalytic RNAs

Ribozymes, or catalytic RNAs, were discovered a little more than 15 years ago. They are found in the organelles of plants and lower eukaryotes, in amphibians, in prokaryotes, in bacteriophages, and in viroids and satellite viruses that infect plants. An example is also known of a ribozyme in hepatitis delta virus, a serious human pathogen. Additional ribozymes are bound to be found in the future, and it is tempting to regard the RNA component(s) of various ribonucleoprotein complexes as the catalytic engine, while the proteins serve as mere scaffolding - an unheard-of notion 15 years ago! In nature, ribozymes are involved in the processing of RNA precursors. However, all the characterized ribozymes have been converted, with some clever engineering, into RNA enzymes that can cleave or modify targeted RNAs (or even DNAs) without becoming altered themselves. While their success in vitro is unquestioned, ribozymes are increasingly used in vivo as valuable tools for studying and regulating gene expression. This review is intended as a brief introduction to the characteristics of the different identified ribozymes and their propertie

G-quadruplex DNA aptamers and their ligands: Structure, function and application

Highly specific and tight-binding nucleic acid aptamers have been selected against a variety of molecular targets for over 20 years. A significant proportion of these oligonucleotides display G-quadruplex structures, particularly for DNA aptamers, that enable molecular recognition of their ligands. G-quadruplex structures couple a common scaffold to varying loop motifs that act in target recognition. Here, we review DNA G-quadruplex aptamers and their ligands from a structural and functional perspective. We compare the diversity of DNA G-quadruplex aptamers selected against multiple ligand targets, and consider structure with a particular focus on dissecting the thrombin binding aptamer - thrombin interaction. Therapeutic and analytical applications of DNA G-quadruplex aptamers are also discussed. Understanding DNA G-quadruplex aptamers carries implications not only for therapeutics and diagnostics, but also in the natural biochemistry of guanine-rich nucleic acids. © 2012 Bentham Science Publishers.postprin

Function and dynamics of aptamers: A case study on the malachite green aptamer

Aptamers are short single-stranded nucleic acids that can bind to their targets with high specificity and high affinity. To study aptamer function and dynamics, the malachite green aptamer was chosen as a model. Malachite green (MG) bleaching, in which an OH- attacks the central carbon (C1) of MG, was inhibited in the presence of the malachite green aptamer (MGA). The inhibition of MG bleaching by MGA could be reversed by an antisense oligonucleotide (AS) complementary to the MGA binding pocket. Computational cavity analysis of the NMR structure of the MGA-MG complex predicted that the OH- is sterically excluded from the C1 of MG. The prediction was confirmed experimentally using variants of the MGA with changes in the MG binding pocket. This work shows that molecular reactivity can be reversibly regulated by an aptamer-AS pair based on steric hindrance. In addition to demonstrate that aptamers could control molecular reactivity, aptamer dynamics was studied with a strategy combining molecular dynamics (MD) simulation and experimental verification. MD simulation predicted that the MG binding pocket of the MGA is largely pre-organized and that binding of MG involves reorganization of the pocket and a simultaneous twisting of the MGA terminal stems around the pocket. MD simulation also provided a 3D-structure model of unoccupied MGA that has not yet been obtained by biophysical measurements. These predictions were consistent with biochemical and biophysical measurements of the MGA-MG interaction including RNase I footprinting, melting curves, thermodynamic and kinetic constants measurement. This work shows that MD simulation can be used to extend our understanding of the dynamics of aptamer-target interaction which is not evident from static 3D-structures. To conclude, I have developed a novel concept to control molecular reactivity by an aptamer based on steric protection and a strategy to study the dynamics of aptamer-target interaction by combining MD simulation and experimental verification. The former has potential application in controlling metabolic reactions and protein modifications by small reactants and the latter may serve as a general approach to study the dynamics of aptamer-target interaction for new insights into mechanisms of aptamer-target recognition

On the entropy of protein families

Proteins are essential components of living systems, capable of performing a huge variety of tasks at the molecular level, such as recognition, signalling, copy, transport, ... The protein sequences realizing a given function may largely vary across organisms, giving rise to a protein family. Here, we estimate the entropy of those families based on different approaches, including Hidden Markov Models used for protein databases and inferred statistical models reproducing the low-order (1-and 2-point) statistics of multi-sequence alignments. We also compute the entropic cost, that is, the loss in entropy resulting from a constraint acting on the protein, such as the fixation of one particular amino-acid on a specific site, and relate this notion to the escape probability of the HIV virus. The case of lattice proteins, for which the entropy can be computed exactly, allows us to provide another illustration of the concept of cost, due to the competition of different folds. The relevance of the entropy in relation to directed evolution experiments is stressed.Comment: to appear in Journal of Statistical Physic

Kui bioloog kohtab keemikut: HIV-1 inhibiitorite otsingul

Väitekirja elektrooniline versioon ei sisalda publikatsioone.HIV-1 on pandeemiline viirus ning nakatatud inimeste arv maailmas suureneb pidevalt. Vaktsiin selle vastu puudub, kuid nakatatud patsientide raviks on kliinilise kasutuse loa saanud ligi 30 erinevat ühendit. Erinevatesse klassidesse kuuluvate inhibiitorite kombineeritud kasutamine (ART) on kujunenud HIV-ga nakatunud patsientide ravimise aluseks. ART ravi kõige olulisemaks puuduseks on ravimite toksilised kõrvaltoimed ning uute resistentsete viiruse tüvede teke. Antud väitekirja põhieesmärgiks oli leida efektiivseid mittetoksilisi ühendeid, mis suruvad maha HIV-1 replikatsiooni (nii metsik-tüüpi viiruse kui ka resistentsete tüvede oma) keskendudes eelkõige pöördtranskriptaasi inhibiitoritele. Kolm gruppi keemilisi ühendeid testiti antiretroviirus-vastase toime suhtes: atsüklilised tümidiini nukleosiidi analoogid, bimorfoliinid ja nende derivaadid ning sahariidhüdrasoonid. Samuti tõestati eksperimentaalselt eelneva in silico skriiningu käigus saadud tulemusi. Käesoleva töö tulemusena töötati välja meetod HIV-1 inhibiitorite skriinimiseks ViraPower lentiviiruse ekspressioonisüsteemi (Invitrogen) põhjal. Meetod on kiire, lihtne, usaldusväärne ning on kõlblik kasutamiseks väljaspool kõrgenenud ohutustasemega laborit (BSL3). Kõige tugevam toime meie laboris uuritud ühenditest oli mitte-nukleosiidsel pöördtranskriptaasi inhibiitoril (NNRTI), mis omas tuntud ravimi Nevirapiiniga sarnast aktiivsust, kuid oli kahjuks mitteaktiivne viiruse resistentsete vormide vastu. Antud ühend leiti ratsionaalse ravimidisaini strateegiat kasutades. Antud töö tulemused võimaldasid täiustada olemasolevat in silico skriiningu meetodit, mis võimaldab tulevikus kavandada uusi ning efektiivsemaid HIV-1 inhibiitoreid.HIV-1 is a pandemic virus and the numbers of infected people are constantly increasing all over the world. There is no vaccine available, but about 30 compounds have been approved by FDA for the treatment of HIV-infected patients. ART (antiretroviral therapy) consists of a combination of at least 3 inhibitors with different mechanism of action. The main drawback of such treatment is side effects of the drugs and the appearance of new resistant forms of the virus. The aim of this work was to find non-toxic compounds which can effectively suppress HIV-1 replication (both wild-type and resistant forms of the virus). We focused our efforts mostly on the discovery of novel reverse transcriptase inhibitors. Three groups of compounds were tested for their antiretroviral activity (acyclic thymine nucleoside analogues, bimorpholines and their derivatives, and saccharide hydrazones); also we experimentally verified the results of the previous in silico screening. As a result of this work, we developed an assay for HIV-1 inhibitors′ screening. This assay is based on ViraPower Lentiviral Expression System (Invitrogen) and is simple, fast, reliable and can be used outside BSL3 facilities. The most potent compound, found by us so far, acts as a non-nucleoside reverse transcriptase inhibitor (NNRTI) and has activity comparable to the activity of a known NNRTI nevirapine, but is unfortunately inactive against the resistant forms of the virus. This compound was found using ration drug design strategy. Most importantly, the results of this work allowed us to improve the existing in silico screening method, which could result in more potent HIV-1 inhibitors in the future

Application of Medicinal Chemistry Methods on Different Classes of Drugs

The present doctoral thesis is the result of the work carried out during the three years of my PhD scholarship at the Rome Center for Molecular Design laboratory (RCMD, Department of Chemistry and Drug Technologies, Sapienza University of Rome), under the supervision of Prof. Rino Ragno. The research activity was focused mainly on the design, optimization and application of computational strategies to derive quantitative structure-activity relationships (QSAR, 3-D QSAR, and COMBINE) on different molecular classes of current interest, such as: opioid receptor antagonists (OPAs), Hepatitis C Virus NS5B-Polymerase Inhibitors (NS5B-NNIs), Hystone Deacetylase Inhibitors (HDACIs), Anti- tubercular agents, vascular endothelial growth factor receptor-2 (VEGFR-2) inhibitors, HSP90 inhibitors, HIV-1 reverse transcriptase inhibitors (NNRTIs), Bovine Serum Amine Oxidase (BSAO) substrates, etc... Moreover two research periods abroad were performed: the first framed in a LLP Erasmus program collaboration, was conducted for six months at the Laboratoire d'Ingénierie et Moléculaire Pharmacologique Biochimie (LIMBP) of the Université de Lorraine Metz (France), directed by Prof. Gilbert Kirsch, and characterized by the application of organic synthesis to obtain new thienopyrimidinone derivatives as potential inhibitors of vascular endothelial growth factor receptor-2 (VEGFR-2); the second took place, for three months, at the Department of Biochemistry and Molecular Biophysics in Washington University School of Medicine in Saint Louis (MO, USA), under the supervision of Prof. Garland R. Marshall, investigating the activity profile of new Histone Deacetylases (HDACs) inhibitors by the application of the Mobility Shift Assay Technology. Main purpose of this doctoral thesis is to highlight the activities carried out in the different research projects, the applied methodologies and the obtained results. The text starts describing those studies whose results were published in scientific journals (chapters I-VI): the author decided to omit some procedural details, completely reported in the published papers, that would make the text too long, tedious and redundant; therefore readers who want to delve these aspects can also refer to Chapter XII in which is possible to read the original papers; on the contrary for studies that have not yet been published, as those characterizing the Chapters VII and VIII, discussion is adequately detailed. Chapters IX and X report the scientific activities carried out in France and in USA respectively; Chapter XI summarizes all the scientific activities accomplished during the entire PhD course, whereas Chapter XII, as mentioned, contains the published articles

Discovery and Selection of Hepatitis B Virus-Derived T Cell Epitopes for Global Immunotherapy Based on Viral Indispensability, Conservation, and HLA-Binding Strength

Immunotherapy represents an attractive option for the treatment of chronic hepatitis B virus (HBV) infection. The HBV proteins polymerase (Pol) and HBx are of special interest for antigen-specific immunotherapy because they are essential for viral replication and have been associated with viral control (Pol) or are still expressed upon viral DNA integration (HBx). Here, we scored all currently described HBx- and Pol-derived epitope sequences for viral indispensability and conservation across all HBV genotypes. This yielded 7 HBx-derived and 26 Po