Biology subjects

Radakovic, A.

Publications and source records attributed to Radakovic, A..

9 recordsLinked to original sources

bioRxiv2024

Stereoselectivity of Aminoacyl-RNA Loop-closing Ligation

The origin of amino acid homochirality remains an unresolved question in the origin of life. The requirement of enantiopure nucleotides for nonenzymatic RNA copying strongly suggests that homochirality of nucleotides and RNA arose early. However, this leaves open the question of whether and how homochiral RNA subsequently imposed biological homochirality on other metabolites including amino acids. Previous studies have reported moderate stereoselectivity for various aminoacyl-RNA transfer reactions. Here we examine aminoacyl-RNA loop-closing ligation, a reaction that captures aminoacylated RNA in a stable phosphoramidate product, such that the amino acid bridges two nucleotides in the RNA backbone. We find that the rate of this reaction is much higher for RNA aminoacylated with L-amino acids than D-amino acids. We present an RNA sequence that near-exclusively captures L-amino acids in loop-closing ligation. Finally, we demonstrate that ligation of aminoacyl-L-RNA results in inverse stereoselectivity for D-amino acids. The observed stereochemical link between D-RNA and L-amino acids in the synthesis of RNA stem-loops containing bridging amino acids constitutes a stereoselective structure building process. We suggest that this process led to a selection for the evolution of aminoacyl-RNA synthetase ribozymes that were selective for L-amino acids, thereby setting the stage for the subsequent evolution of homochiral peptide and ultimately protein synthesis.

biochemistry↗

bioRxiv2024

Nanopore sequencing of intact aminoacylated tRNAs

Transfer RNAs (tRNA) are decorated during biogenesis with a variety of modifications that modulate their stability, aminoacylation, and decoding potential during translation. The complex landscape of tRNA modification presents significant analysis challenges and to date no single approach enables the simultaneous measurement of important but disparate chemical properties of individual, mature tRNA molecules. We developed a new, integrated approach to analyze the sequence, modification, and aminoacylation state of tRNA molecules in a high throughput nanopore sequencing experiment, leveraging a chemical ligation that embeds the charged amino acid in an adapted tRNA molecule. During nanopore sequencing, the embedded amino acid generates unique distortions in ionic current and translocation speed, enabling application of machine learning approaches to classify charging status and amino acid identity. Specific applications of the method indicate it will be broadly useful for examining relationships and dependencies between tRNA sequence, modification, and aminoacylation.

molecular biology↗

bioRxiv2024

Autocatalytic assembly of a chimeric aminoacyl-RNA synthetase ribozyme

Autocatalytic reactions driving the self-assembly of biological polymers are important for the origin of life, yet few experimental examples of such reactions exist. Here we report an autocatalytic assembly pathway that generates a chimeric, amino acid-bridged aminoacyl-RNA synthetase ribozyme. The noncovalent complex of ribozyme fragments initiates low level aminoacylation of one of the fragments, which after loop-closing ligation generates a highly active covalently-linked chimeric ribozyme. The generation of this ribozyme is increasingly efficient over time due to the autocatalytic assembly cycle that sustains the ribozyme over indefinite cycles of serial dilution. Due to its trans activity, this ribozyme also assembles ribozymes distinct from itself, such as the hammerhead, suggesting that RNA aminoacylation, coupled with nonenzymatic ligation, could have facilitated the emergence and propagation of ribozymes.

biochemistry↗

bioRxiv2024

RNA complexes with nicks and gaps: thermodynamic and kinetic effects of coaxial stacking and dangling ends

Multiple RNA strands can interact in solution and assume a large variety of configurations dictated by their potential for base pairing. Although duplex formation from two complementary oligonucleotides has been studied in detail, we still lack a systematic characterization of the behavior of higher order complexes. Here we focus on the thermodynamic and kinetic effects of an upstream oligonucleotide on the binding of a downstream oligonucleotide to a common template, as we vary the sequence and structure of the contact interface. We show that coaxial stacking in RNA is well correlated with but much more stabilizing than helix propagation over an analogous intact double helix step (median {Delta} {Delta} G37{degrees}C {approx} 1.7 kcal/mol). Consequently, approximating coaxial stacking in RNA with the helix propagation term leads to large discrepancies between predictions and our experimentally determined melting temperatures, with an offset of {approx} 10{degrees}C. Our kinetic study reveals that the hybridization of the downstream probe oligonucleotide is impaired (lower kon) by the presence of the upstream oligonucleotide, with the thermodynamic stabilization coming entirely from an extended lifetime (lower koff) of the bound downstream oligonucleotide, which can increase from seconds to months. Surprisingly, we show that the effect of nicks is dependent on the length of the stacking oligonucleotides, and we discuss the binding of ultrashort (1 [~] 4 nt) oligonucleotides that are relevant in the context of the origin of life. The thermodynamic and kinetic data obtained in this work allow for the prediction of the formation and stability of higher order multi-stranded complexes. Graphic entry for the Table of Contents (TOC) O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/589350v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@8b11d3org.highwire.dtl.DTLVardef@3f55c6org.highwire.dtl.DTLVardef@185703org.highwire.dtl.DTLVardef@1f8a9e8_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2024

Structure-guided aminoacylation and assembly of chimeric RNAs

Coded ribosomal peptide synthesis could not have evolved unless its sequence and amino acid specific aminoacylated tRNA substrates already existed. We therefore wondered whether aminoacylated RNAs might have served some primordial function prior to their role in protein synthesis. Here we show that specific RNA sequences can be nonenzymatically aminoacylated and ligated to produce amino acid-bridged stem-loop RNAs. We used deep sequencing to identify RNAs that undergo highly efficient glycine aminoacylation followed by loop-closing ligation. The crystal structure of one such glycine-bridged RNA hairpin reveals a compact internally stabilized structure with the same eponymous T-loop architecture found in modern tRNA. We demonstrate that the T-loop assisted amino acid bridging of RNA oligonucleotides enables the rapid template-free assembly of a chimeric version of an aminoacyl-RNA synthetase ribozyme. We suggest that the primordial assembly of such chimeric ribozymes would have allowed the greater functionality of amino acids to contribute to enhanced ribozyme catalysis, providing a driving force for the evolution of sequence and amino acid specific aminoacyl-RNA synthetase enzymes prior to their role in protein synthesis.

biochemistry↗

bioRxiv2023

Direct monitoring of the thermodynamics and kinetics of DNA and RNA dinucleotide dehybridization from gaps and overhangs

Hybridization of short nucleic acid segments (<4 nucleotides) to single-strand templates occurs as a critical intermediate in processes such as non-enzymatic nucleic acid replication and toehold-mediated strand displacement. These templates often contain adjacent duplex segments that stabilize base pairing with single-strand gaps or overhangs, but the thermodynamics and kinetics of hybridization in such contexts are poorly understood due to experimental challenges of probing weak binding and rapid structural dynamics. Here we develop an approach to directly measure the thermodynamics and kinetics of DNA and RNA dinucleotide dehybridization using steady-state and temperature-jump infrared spectroscopy. Our results suggest that dinucleotide binding is stabilized through coaxial stacking interactions with the adjacent duplex segments as well as from potential non-canonical base pairing configurations and structural dynamics of gap and overhang templates revealed using molecular dynamics simulations. We measure timescales for dissociation ranging from 0.2 to 40 {micro}s depending on the template and temperature. Dinucleotide hybridization and dehybridization involves a significant free energy barrier with characteristics resembling that of canonical oligonucleotides. Together, our work provides an initial step for predicting the stability and kinetics of hybridization between short nucleic acid segments and various templates.

biophysics↗

bioRxiv2021

Non-enzymatic assembly of active chimeric ribozymes from aminoacylated RNA oligonucleotides

Aminoacylated tRNAs, which harbor a covalent linkage between amino acids and RNA, are a universally conserved feature of life. Because they are essential substrates for ribosomal translation, aminoacylated oligonucleotides must have been present in the RNA World prior to the evolution of the ribosome. One possibility we are exploring is that the aminoacyl ester linkage served another function before being recruited for ribosomal protein synthesis. The nonenzymatic assembly of ribozymes from short RNA oligomers under realistic conditions remains a key challenge in demonstrating a plausible pathway from prebiotic chemistry to the RNA World. Here, we show that aminoacylated RNAs can undergo template-directed assembly into chimeric amino acid-RNA polymers that are active ribozymes. We demonstrate that such chimeric polymers can retain the enzymatic function of their all-RNA counterparts by generating chimeric hammerhead, RNA ligase, and aminoacyl transferase ribozymes. Amino acids with diverse side chains form linkages that are well tolerated within the RNA backbone, potentially bringing novel functionalities to ribozyme catalysis. Our work suggests that aminoacylation chemistry may have played a role in primordial ribozyme assembly. Increasing the efficiency of this process provides an evolutionary rationale for the emergence of sequence and amino acid specific aminoacyl-RNA synthetase ribozymes, which could then have generated the substrates for ribosomal protein synthesis. Significance StatementThe emergence of the primordial ribosome from the RNA World would have required access to aminoacylated RNA substrates. The spontaneous generation of such substrates without enzymes is inefficient, and it remains unclear how they could be selected for in a prebiotic milieu. In our study we identify a role for aminoacylated RNA in ribozyme assembly, a longstanding problem in the origin of life research. We show that aminoacylated RNAs, but not unmodified RNAs, rapidly assemble into chimeric amino acid-bridged ribozymes that retain their native enzymatic activity. Our work therefore addresses two key challenges within the origin-of-life field: we demonstrate assembly of functional ribozymes and we identify a potential evolutionary benefit for RNA aminoacylation that is independent of coded peptide translation.

biochemistry↗

bioRxiv2020

A Potential Role for Aminoacylation in Primordial RNA Copying Chemistry

Aminoacylated tRNAs are the substrates for ribosomal protein synthesis in all branches of life, implying an ancient origin for aminoacylation chemistry. In the 1970s, Orgel and colleagues reported potentially prebiotic routes to aminoacylated nucleotides and their RNA templated condensation to form amino acid bridged dinucleotides. However, it is unclear whether such reactions would have aided or impeded nonenzymatic RNA replication. Determining whether aminoacylated RNAs could have been advantageous in evolution prior to the emergence of protein synthesis remains a key challenge. We therefore tested the ability of aminoacylated RNA to participate in both templated primer extension and ligation reactions. We find that at low magnesium concentrations that favor fatty acid-based protocells, these reactions proceed orders of magnitude more rapidly than when initiated from the cis-diol of unmodified RNA. We further demonstrate that amino acid bridged RNAs can act as templates in a subsequent round of copying. Our results suggest that aminoacylation facilitated nonenzymatic RNA replication, thus outlining a potentially primordial functional link between aminoacylation chemistry and RNA replication. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=106 SRC="FIGDIR/small/413815v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@1e5f29dorg.highwire.dtl.DTLVardef@19b2a99org.highwire.dtl.DTLVardef@9aad0org.highwire.dtl.DTLVardef@ad47f7_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2019

Prebiotically Plausible ‘Patching’ of RNA Backbone Cleavage Through a 3′-5′ Pyrophosphate Linkage

Achieving multiple cycles of RNA replication within a model protocell would be a critical step towards demonstrating a path from prebiotic chemistry to cellular biology. Any model for early life based on an RNA world must account for RNA strand cleavage and hydrolysis, which would degrade primitive genetic information and lead to an accumulation of truncated, phosphate-terminated strands. We show here that cleavage of the phosphodiester backbone is not an endpoint for RNA replication. Instead, 3' -phosphate terminated RNA strands are able to participate in template-directed copying reactions with activated ribonucleotide monomers. These reactions form a pyrophosphate linkage, the stability of which we have characterized in the context of RNA copying chemistry. We found that the pyrophosphate bond is relatively stable within an RNA duplex and in the presence of chelated magnesium. Under these conditions, pyrophosphate-RNA can act as a temporary patch to template the polymerization of canonical ribonucleotides, suggesting a plausible non-enzymatic pathway for the salvage and recovery of genetic information following strand cleavage.

biochemistry↗