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Defining RNA motif-aminoglycoside interactions via two-dimensional combinatorial screening and structure-activity relationships through sequencing.

ABSTRACT: RNA is an extremely important target for the development of chemical probes of function or small molecule therapeutics. Aminoglycosides are the most well studied class of small molecules to target RNA. However, the RNA motifs outside of the bacterial rRNA A-site that are likely to be bound by these compounds in biological systems is largely unknown. If such information were known, it could allow for aminoglycosides to be exploited to target other RNAs and, in addition, could provide invaluable insights into potential bystander targets of these clinically used drugs. We utilized two-dimensional combinatorial screening (2DCS), a library-versus-library screening approach, to select the motifs displayed in a 3×3 nucleotide internal loop library and in a 6-nucleotide hairpin library that bind with high affinity and selectivity to six aminoglycoside derivatives. The selected RNA motifs were then analyzed using structure-activity relationships through sequencing (StARTS), a statistical approach that defines the privileged RNA motif space that binds a small molecule. StARTS allowed for the facile annotation of the selected RNA motif-aminoglycoside interactions in terms of affinity and selectivity. The interactions selected by 2DCS generally have nanomolar affinities, which is higher affinity than the binding of aminoglycosides to a mimic of their therapeutic target, the bacterial rRNA A-site.

SUBMITTER: Velagapudi SP

PROVIDER: S-EPMC3789863 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

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Defining RNA motif-aminoglycoside interactions via two-dimensional combinatorial screening and structure-activity relationships through sequencing.

Velagapudi Sai Pradeep SP Disney Matthew D MD

Bioorganic & medicinal chemistry 20130507 20

RNA is an extremely important target for the development of chemical probes of function or small molecule therapeutics. Aminoglycosides are the most well studied class of small molecules to target RNA. However, the RNA motifs outside of the bacterial rRNA A-site that are likely to be bound by these compounds in biological systems is largely unknown. If such information were known, it could allow for aminoglycosides to be exploited to target other RNAs and, in addition, could provide invaluable i ...[more]

PMID: 23719281

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Project description:RNAs have diverse structures that are important for biological function. These structures include bulges and internal loops that can form tertiary contacts or serve as ligand binding sites. The most commonly exploited RNA drug target for small molecule intervention is the bacterial ribosome, more specifically the rRNA aminoacyl-tRNA site (rRNA A-site) which is a major target for the aminoglycoside class of antibiotics. The bacterial A-site is composed of a 1 x 1 nucleotide all-U internal loop and a 2 x 1 nucleotide all-A internal loop separated by a single GC base pair. Therefore, we probed the molecular recognition of a small library of four aminoglycosides for binding a 16384-member bacterial rRNA A-site-like internal loop library using two-dimensional combinatorial screening (2DCS). 2DCS is a microarray-based method that probes RNA and chemical spaces simultaneously. These studies sought to determine if aminoglycosides select their therapeutic target if given a choice of binding all possible internal loops derived from an A-site-like library. Results show that the bacterial rRNA A-site was not selected by any aminoglycoside. Analyses of selected sequences using the RNA Privileged Space Predictor (RNA-PSP) program show that each aminoglycoside preferentially binds different types of internal loops. For three of the aminoglycosides, 6''-azido-kanamycin A, 5-O-(2-azidoethyl)-neamine, and 6''-azido-tobramycin, the selected internal loops bind with approximately 10-fold higher affinity than the bacterial rRNA A-site. The internal loops selected to bind 5''-azido-neomycin B bind with an affinity similar to that of the therapeutic target. Selected internal loops that are unique for each aminoglycoside have dissociation constants ranging from 25 to 270 nM and are specific for the aminoglycoside they was selected to bind compared to the other arrayed aminoglycosides. These studies further establish a database of RNA motifs that are recognized by small molecules that could be used to enable the rational and modular design of small molecules targeting RNA.

Project description:We describe a new method for encoded synthesis, efficient on-resin screening, and rapid unambiguous sequencing of combinatorial peptide libraries. An improved binary tag system for encoding peptide libraries during synthesis was designed to facilitate unequivocal assignment of isobaric residues by MALDI-TOF MS analysis. The improved method for encoded library synthesis was combined with a new versatile on-resin screening strategy that permitted multiple stages and types of screening to be employed successively on one library under mild conditions. The new method facilitated a combinatorial study of transglutaminase (TGase) enzyme substrate peptides, revealing new details of the effect of amino acid composition on TGase substrates. The approach was first demonstrated for an encoded library (130,321 compounds) of lysine pentapeptide substrates of TGase, synthesized using the "split-mix" method. The library was reacted on-resin with TGase enzyme and a soluble desthiobiotin labeled glutamine substrate. Initial screening was performed by adsorbing streptavidin-coated magnetic microparticles onto library beads, followed by magnetic separation. The differential binding affinities of desthiobiotin and biotin for streptavidin were exploited to release the magnetic microparticles and regenerate the desthiobiotin-labeled resin beads for further screening by flow-cytometry-based automated bead sorting, resulting in 345 beads that were sequenced by MALDI-TOF MS analysis. A second library consisted of encoded glutamine hexapeptide substrates, which was reacted on-resin with TGase enzyme and a soluble desthiobiotin-labeled cadaverine. Two-stage screening identified 267 glutamine peptides as TGase-reactive, of which 21 were further analyzed by solution-phase enzyme kinetics. Kinetic results indicated that the peptide PQQQYV from the library has a 68-fold greater substrate specificity than the best known glutamine substrate QQIV. The new encoding and screening strategies described here are expected to be broadly applicable to synthesis and screening of combinatorial peptide libraries in the future.

Dataset Information

Defining RNA motif-aminoglycoside interactions via two-dimensional combinatorial screening and structure-activity relationships through sequencing.

Publications

Defining RNA motif-aminoglycoside interactions via two-dimensional combinatorial screening and structure-activity relationships through sequencing.

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