5 research outputs found
Simultaneous prediction of RNA secondary structure and helix coaxial stacking
BACKGROUND: RNA secondary structure plays a scaffolding role for RNA tertiary conformation. Accurate secondary structure prediction can not only identify double-stranded helices and single stranded-loops but also help provide information for potential tertiary interaction motifs critical to the 3D conformation. The average accuracy in ab initio prediction remains 70%; performance improvement has only been limited to short RNA sequences. The prediction of tertiary interaction motifs is difficult without multiple, related sequences that are usually not available. This paper presents research that aims to improve the secondary structure prediction performance and to develop a capability to predict coaxial stacking between helices. Coaxial stacking positions two helices on the same axis, a tertiary motif present in almost all junctions that account for a high percentage of RNA tertiary structures. RESULTS: This research identified energetic rules for coaxial stacks and geometric constraints on stack combinations, which were applied to developing an efficient dynamic programming application for simultaneous prediction of secondary structure and coaxial stacking. Results on a number of non-coding RNA data sets, of short and moderately long lengths, show a performance improvement (specially on tRNAs) for secondary structure prediction when compared with existing methods. The program also demonstrates a capability for prediction of coaxial stacking. CONCLUSIONS: The significant leap of performance on tRNAs demonstrated in this work suggests that a breakthrough to a higher performance in RNA secondary structure prediction may lie in understanding contributions from tertiary motifs critical to the structure, as such information can be used to constrain geometrically as well as energetically the space of RNA secondary structure
Simultaneous prediction of RNA secondary structure and helix coaxial stacking
Abstract Background RNA secondary structure plays a scaffolding role for RNA tertiary conformation. Accurate secondary structure prediction can not only identify double-stranded helices and single stranded-loops but also help provide information for potential tertiary interaction motifs critical to the 3D conformation. The average accuracy in ab initio prediction remains 70%; performance improvement has only been limited to short RNA sequences. The prediction of tertiary interaction motifs is difficult without multiple, related sequences that are usually not available. This paper presents research that aims to improve the secondary structure prediction performance and to develop a capability to predict coaxial stacking between helices. Coaxial stacking positions two helices on the same axis, a tertiary motif present in almost all junctions that account for a high percentage of RNA tertiary structures. Results This research identified energetic rules for coaxial stacks and geometric constraints on stack combinations, which were applied to developing an efficient dynamic programming application for simultaneous prediction of secondary structure and coaxial stacking. Results on a number of non-coding RNA data sets, of short and moderately long lengths, show a performance improvement (specially on tRNAs) for secondary structure prediction when compared with existing methods. The program also demonstrates a capability for prediction of coaxial stacking. Conclusions The significant leap of performance on tRNAs demonstrated in this work suggests that a breakthrough to a higher performance in RNA secondary structure prediction may lie in understanding contributions from tertiary motifs critical to the structure, as such information can be used to constrain geometrically as well as energetically the space of RNA secondary structure.</p
Engineering protein biosynthesis apparatus, advanced design and screening strategies for small and fluorinated substrates in orthogonal translation
Protein engineering is a comprehensive toolbox for the chemical modification of enzymes in particular, and for the expansion of molecular functional diversity in general. In recent decades, two different categories have become established for the engineering of proteins. These include the approach of directed evolution approaches on the one hand and the strategies of rational protein design on the other hand. In particular, the use of noncanonical amino acids to introduce new functionalities has gained importance in the engineersâ toolbox. These include isostructural analogues of canonical amino acids as well as molecules with reactivities that can provide sites for further protein modifications.
In this study, we have presented a strategy for manipulating the protein biosynthesis machinery towards the incorporation of noncognate fluorinated substrates. In general, fluorinated amino acids are not genetically encoded. These mainly synthetic building block are valuable for the design of particularly stable protein folds and for targeting highly specific protein-protein interactions. Fluorine is small and has a very low polarizability and the strongest inductive effect among the chemical elements found on earth. Due to these unique stereoelectronic properties, fluorine substitution is advantageously used in protein and peptide design. In this context, the strategy of directed evolution was applied to construct isoleucyl-transfer ribonucleic acid synthetase libraries for the isoleucine AUA rare codon reassignment with small aliphatic fluorinated amino acids, such as L-trifluoroethylglycine, by random mutagenesis. A suitable screening plasmid containing a mutant of superfolder green fluorescent protein (sfGFP) as reporter protein and a modified isoleucine transfer ribonucleic acid (tRNA_UAU) from Escherichia coli was produced to create an enhanced molecular adaptor level for gene expression. However, the required selection strain could not be constructed by genome editing due to the complexity of essential gene modification.
In the second part of the study, different reporter proteins were used in advanced design with noncanonical amino acids for improvement of their biophysical, chemical, and biological properties. A robust alkene-tagged sfGFP variant was obtained, which is a valuable target in medicinal chemistry. In addition, the residue-specific incorporation of proline analogues into green fluorescent protein (GFP) derivates â enhanced green fluorescent protein (EGFP), NowGFP, and KillerOrange â enables the study of the role of prolines in the typical ÎČ-barrel structure organization
Ătude du ribozyme SOFA-HDV comme outil molĂ©culaire : application et optimisation
Les avancĂ©es en biologie molĂ©culaire et cellulaire des derniĂšres dĂ©cennies ont permis de redĂ©finir le rĂŽle de lâARN au sein des cellules de tous les domaines du vivant. Initialement cantonnĂ© dans un rĂŽle de support transitoire de lâinformation gĂ©nĂ©tique du gĂ©nome (ADN) en direction des effecteurs ou molĂ©cules actives (protĂ©ines et mĂ©tabolites), lâARN est maintenant associĂ© Ă toutes les sphĂšres de la biologie. Les molĂ©cules dâARN peuvent agir autant comme gĂ©nome (virus), comme molĂ©cules adaptatrices (ARNt), comme messager de lâinformation gĂ©nĂ©tique (ARNm), comme enzyme (ribozyme) ou encore comme molĂ©cules rĂ©gulatrices en cis (riboswitch) ou en trans (miARN). Nous savons aussi que la grande majoritĂ© du gĂ©nome des cellules eucaryotes est transcrite Ă un moment ou un autre. Ces implications de lâARN en font une cible de choix pour la recherche en gĂ©nomique fonctionnelle, ainsi que pour des applications thĂ©rapeutiques. Câest pourquoi, depuis la dĂ©couverte des ARN catalytiques et de lâinterfĂ©rence Ă lâARN, beaucoup dâefforts ont Ă©tĂ© consacrĂ©s pour dĂ©velopper un Ă©ventail dâoutils molĂ©culaires permettant dâinhiber lâexpression de gĂšnes dâintĂ©rĂȘt. Le dĂ©fi qui se dessine aujourdâhui est le dĂ©veloppement dâoutils plus spĂ©cifiques et plus efficaces, entre autres parce que la variĂ©tĂ© dâARN quâun inhibiteur peut rencontrer est beaucoup plus grande quâinitialement estimĂ©e. De plus, les donnĂ©es recueillies lors dâessais cliniques montrent la nĂ©cessitĂ© de combiner un trĂšs grand potentiel avec une spĂ©cificitĂ© accrue. Les travaux de cette thĂšse se concentrent sur un outil molĂ©culaire qui a le potentiel de rĂ©pondre positivement Ă ce dĂ©fi : le ribozyme SOFA-HDV. Mon projet de recherche visait Ă dĂ©montrer le potentiel de cet ARN catalytique pour le ciblage de gĂšnes in cellulo et de dĂ©velopper son application. Tout dâabord, jâai dĂ©montrĂ© que le ribozyme SOFA-HDV pouvait ĂȘtre utilisĂ© pour inhiber la fonction dâun ARN in cellulo. Cette Ă©tude a Ă©galement mis en Ă©vidence lâusage de ce ribozyme comme agent antiviral, avec le virus de lâhĂ©patite C comme modĂšle. Le dĂ©veloppement de nouvelles thĂ©rapies plus performantes avec peu dâeffets secondaires demeure un enjeu important. Au moment de publier ces travaux, en plus dâĂȘtre le premier exemple exhaustif de lâutilisation du ribozyme SOFA-HDV in cellulo, notre Ă©tude contenait le plus grand nombre de ribozymes jamais testĂ©s contre le VHC en une seule publication. Bien que modeste, lâeffet observĂ© dĂ©montre que ce ribozyme peut inhiber la rĂ©plication dâun virus dans un modĂšle in cellulo. Nos rĂ©sultats exposent aussi la diffĂ©rence dâaccessibilitĂ© entre les ARN de polaritĂ©s positive et nĂ©gative du VHC in cellulo. Par la suite, jâai participĂ© au dĂ©veloppement de ribozymes SOFA-HDV ciblant le virus de l'immunodĂ©ficience humaine (VIH) dans le cadre dâune collaboration. Parmi les ribozymes testĂ©s, nous en avons identifiĂ© un dont lâactivitĂ© catalytique rĂ©duit la rĂ©plication du VIH de plus de 50 % dans un modĂšle cellulaire. Dans le cadre de cette Ă©tude, nous avons identifiĂ© un site hautement favorable pour le ciblage par un ribozyme SOFA-HDV ou par un shARN. Des donnĂ©es suggĂšrent aussi une spĂ©cificitĂ© Ă©levĂ©e du ribozyme SOFA-HDV. Des tests dâinhibition avec diffĂ©rentes souches du VIH montrent que lâactivitĂ© du ribozyme est affectĂ©e avec un seul mĂ©sappariement entre le biosenseur (Ă©lĂ©ment du module SOFA resposable de reconnaissance du substrat) et son site de liaison. Finalement, dans un esprit dâintĂ©gration des connaissances recueillies au fil des diffĂ©rents projets impliquant le ribozyme SOFA-HDV, je me suis intĂ©ressĂ© Ă leur processus de sĂ©lection pour le ciblage gĂ©nique. Jâai dĂ©montrĂ© lâimpact de la sĂ©quence du biosenseur sur lâactivitĂ© du ribozyme. Jâai Ă©galement illustrĂ© lâautocoupure possible lorsque la sĂ©quence du biosenseur crĂ©e un prolongement du bloqueur (Ă©lĂ©ment du module SOFA agissant comme verrou) ainsi que lâimpact de la structure du substrat autant au niveau des sites de liaison du domaine de reconnaissance que du biosenseur. Ces nouveaux Ă©lĂ©ments combinĂ©s aux donnĂ©es antĂ©rieures sur le ribozyme HDV original mâont permis dâĂ©laborer une marche Ă suivre pour la prĂ©sĂ©lection des ribozymes SOFA-HDV selon leur potentiel comme ciseaux molĂ©culaires. En conclusion, ces travaux ont contribuĂ© Ă mettre de lâavant le potentiel du ribozyme SOFA-HDV pour des applications de ciblage de gĂšnes, plus particuliĂšrement pour des cibles virales. De ce fait, il existe maintenant des exemples concrets de lâutilisation de ce ribozyme en cellules humaines. Tout indique que la spĂ©cificitĂ© du module SOFA est prĂ©servĂ©e in cellulo et serait avantageusement comparable Ă dâautres technologies. Globalement, cette thĂšse devrait rendre lâutilisation du ribozyme SOFA-HDV plus accessible et favoriser son dĂ©veloppement comme outil molĂ©culaire