Biology subjects

Piccirilli, J. A.

Publications and source records attributed to Piccirilli, J. A..

8 recordsLinked to original sources

bioRxiv2026

A transient third metal ion shapes the catalytic cycle of a group I intron ribozyme

The self-splicing group I intron ribozyme from Tetrahymena thermophillia (THr) is a prototypical example of how RNA overcomes its limited chemical repertoire to form complex, negatively charged junctions and catalyze chemical reactions. Despite over 30 years of biochemical and structural characterization, questions still remain regarding the requirements for THr catalysis that may inform structure based drug design against group I introns, as well as the use of THr as an RNA editing tool. Recent cryo-EM structures have provided an unprecedented window into the first and second steps of splicing, enabling detailed mechanistic investigation at the atomistic level. In this work, we leverage solvation theory, molecular dynamics, alchemical free energy simulations, and machine learning accelerated QM/MM to probe outstanding questions related to 1) the role of a possible third Mg2+ binding in the active site, 2) differences in catalytic requirements between Gexo cofactors and between the first and second steps of splicing, 3) the potential role of an acid or base, and 4) restrictions on the identity of the 5' exon splice site nucleotide, U(-1). We propose that a transient, cofactor dependent, interaction with a third metal participates in the first step, while a higher affinity interaction with this third ion is required in the second step. We also propose that the presence of a phosphate on the Gexo in the first step, and analogously the G{omega} in the second step, forms a metal ion binding site not present when guanosine is bound. Finally, we propose and computationally test design modifications of G22 (isofunctional substitutions of 2,6-diaminopurine that tune the pKa at the N1 position) that we predict will enable the accommodation of C(-1) in a crucial wobble-like pair at physiological pH. This design would provide a potential strategy for expanding the sequence space accessible to programmable trans-splicing ribozymes in RNA editing applications.

biophysics↗

bioRxiv2025

Functional relevance of CASP16 nucleic acid predictions as evaluated by structure providers

Accurate biomolecular structure prediction enables the prediction of mutational effects, the speculation of function based on predicted structural homology, the analysis of ligand binding modes, experimental model building and many other applications. Such algorithms to predict essential functional and structural features remain out of reach for biomolecular. Here, we report quantitative and qualitative evaluation of nucleic acid structures for the CASP16 blind prediction challenge by 12 of the experimental groups who provided nucleic acid targets. Blind predictions accurately model secondary structure and some aspects of tertiary structure, including reasonable global folds for some complex RNAs, however, predictions often lack accuracy in the regions of highest functional importance. All models have inaccuracies in non-canonical regions where, e.g., the nucleic-acid backbone bends or a base forms a non-standard hydrogen bond. These bends and non-canonical interactions are integral to form functionally important regions such as RNA enzymatic active sites. Additionally, the modeling of conserved and functional interfaces between nucleic acids and ligands, proteins, or other nucleic acids remains poor. For some targets, the experimental structures may not represent the only structure the biomolecular complex occupies in solution or in its functional life-cycle, posing a future challenge for the community.

biophysics↗

bioRxiv2024

Mechanistic Studies of Small Molecule Ligands Selective to RNA Single G Bulges

Small-molecule RNA binders have emerged as an important pharmacological modality. A profound understanding of the ligand selectivity, binding mode, and influential factors governing ligand engagement with RNA targets is the foundation for rational ligand design. Here, we report a novel class of coumarin derivatives exhibiting selective binding affinity towards single G RNA bulges. Harnessing the computational power of all-atom Gaussian accelerated Molecular Dynamics (GaMD) simulations, we unveiled a rare minor groove binding mode of the ligand with a key interaction between the coumarin moiety and the G bulge. This predicted binding mode is consistent with results obtained from structure-activity-relationship (SAR) studies and transverse relaxation measurements by NMR spectroscopy. We further generated 444 molecular descriptors from 69 coumarin derivatives and identified key contributors to the binding events, such as charge state and planarity, by lasso (least absolute shrinkage and selection operator) regression. Strikingly, small structure perturbations on these key contributors, such as the addition of a methyl group that disrupts the planarity of the ligand resulted in > 100-fold reduction in the binding affinity. Our work deepened the understanding of RNA-small molecule interactions and integrated a new generalizable platform for the rational design of selective small-molecule RNA binders.

biochemistry↗

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

Post-Transcriptional Methylation of Mitochondrial-tRNA Differentially Contributes to Mitochondrial Pathology

Human mitochondrial tRNAs (mt-tRNAs), critical for mitochondrial biogenesis, are frequently associated with pathogenic mutations. These mt-tRNAs have unusual sequence motifs and require post-transcriptional modifications to stabilize their fragile structures. However, whether a modification that stabilizes a wild-type (WT) mt-tRNA structure would also stabilize its pathogenic variants is unknown. Here we show that the N1-methylation of guanosine at position 9 (m1G9) of mt-Leu(UAA), while stabilizing the WT tRNA, has an opposite and destabilizing effect on variants associated with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes). This differential effect is further demonstrated by the observation that demethylation of m1G9, while damaging to the WT tRNA, is beneficial to the major pathogenic variant, improving its structure and activity. These results have new therapeutic implications, suggesting that the N1-methylation of mt-tRNAs at position 9 is a determinant of pathogenicity and that controlling the methylation level is an important modulator of mt-tRNA-associated diseases.

cell biology↗

bioRxiv2023

Genome-Wide Profiling of tRNA Using an Unexplored Reverse Transcriptase with High Processivity

Monitoring the dynamic changes of cellular tRNA pools is challenging, due to the extensive post-transcriptional modifications of individual species. The most critical component in tRNAseq is a processive reverse transcriptase (RT) that can read through each modification with high efficiency. Here we show that the recently developed group-II intron RT Induro has the processivity and efficiency necessary to profile tRNA dynamics. Using our Induro-tRNAseq, simpler and more comprehensive than the best methods to date, we show that Induro progressively increases readthrough of tRNA over time and that the mechanism of increase is selective removal of RT stops, without altering the misincorporation frequency. We provide a parallel dataset of the misincorporation profile of Induro relative to the related TGIRT RT to facilitate the prediction of non-annotated modifications. We report an unexpected modification profile among human proline isoacceptors, absent from mouse and lower eukaryotes, that indicates new biology of decoding proline codons.

genomics↗

bioRxiv2021

The cardiac lncRNA Chantico directly regulates Cxcl1 chemokine transcription

Withdrawal StatementThe corresponding author has withdrawn this preprint owing to inability to reproduce some of the data, instances of inappropriate data exclusion, and loss of much of the primary experimental records/data. Specifically, Figures 2B,E,H; 3; 4; 5A,B,D; 6; S2A,C; S4A; S5; and S6A,B and attendant text contain analyses for which the primary record and/or raw data no longer exist; the analyses, where still available, suffer from inappropriate data exclusion and thus should not be construed to be an accurate reflection of the experiments. Attempts by others in the lab to repeat several of the experiments in these indicated panels have failed reproduce the presented effects, despite showing much greater precision. Therefore the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author.

molecular biology↗

bioRxiv2021

Sub-3 Angstrom cryo-EM structure of RNA enabled by engineered homomeric self-assembly

Many functional RNAs fold into intricate and precise 3D architectures, and high-resolution structures are required to understand their underlying mechanistic principles. However, RNA structural determination is difficult. Herein, we present a nanoarchitectural strategy to enable the efficient single-particle cryogenic electron microscopy (cryo-EM) analysis of RNA-only structures. This strategy, termed RNA oligomerization-enabled cryo-EM via installing kissing-loops (ROCK), involves the engineering of target RNAs by installing kissing-loop sequences onto functionally nonessential stems for the assembly into closed homomeric nanoarchitectures. Assembly with geometric restraints leads to (1) molecular weight multiplication and (2) structural flexibility mitigation, both beneficial for cryo-EM analysis. Together with construct optimization and symmetry-expansion reconstruction, ROCK yields the cryo-EM reconstruction of the Tetrahymena group I intron at an overall resolution of 2.98 [A] (2.85 [A] resolution for the core domains), enabling the de novo model building of the complete intron RNA including previously unknown peripheral domains. When applied to smaller RNAs, ROCK readily produces modest-resolution maps, revealing the conformational rearrangement of the Azoarcus group I intron and the bound ligand in the FMN riboswitch. Our work unleashes the largely unexplored potential of cryo-EM in RNA structural studies.

biophysics↗