Biology subjects

McRae, E. K. S.

Publications and source records attributed to McRae, E. K. S..

6 recordsLinked to original sources

bioRxiv2026

Lipoproteins modulate the uptake and biological functionof cationic cell-penetrating peptides across the animal lineage.

Cationic cell-penetrating peptides (+CPPs) are pervasive killer peptides produced by all animals and found in innate immune systems, venoms and neurodegenerative diseases. Despite their ubiquity, the mechanisms underlying their uptake remain opaque and intensely debated. Here, we interrogate +CPPs spanning 600 million years of animal evolution and identify endocytosis as a conserved/convergent uptake mechanism across cell types and organisms, at physiological concentrations. By combining multiplex imaging, genetic screening, cryo-electron tomography, and biophysical methods, we uncover that +CPPs seemingly universally enter eukaryote cells via 'hitchhiking' on lipoproteins. We further show that the interaction of +CPPs with lipoproteins modulates their antimicrobial function. Combined, our findings establish a unified molecular framework describing a pan-eukaryote cell penetrance mechanism. As hyperlipidemia is a common comorbidity, our findings have direct implications for human health. Lastly, the insights gleaned from this work highlight design principles that may inform the future engineering of peptide-based therapeutics and delivery vehicles.

cell biology↗

bioRxiv2023

An RNA origami robot that traps and releases a fluorescent aptamer

RNA nanotechnology aims at using RNA as a programmable material to create self-assembling nanodevices for application in medicine and synthetic biology. RNA devices have been developed by adopting mechanisms such as allosteric binding and toehold-mediated strand displacement. There are, however, no examples of RNA "robotic" devices that sense, compute, and actuate through mechanical reconfiguration as has been demonstrated in DNA nanotechnology. Here we use the RNA origami method to prototype an RNA robotic device, named the "Traptamer", that senses two RNA key strands, acts as a Boolean AND gate, and activates the fluorescent aptamer iSpinach through release from a mechanical trap. The Traptamer depends on binding of two different RNA key strands to achieve full activation and can be reversed by addition of two complementary RNA anti-key strands. Cryo-EM of the closed Traptamer structure at 5.45 [A] resolution reveals a hinge-like mechanical distortion of the iSpinach motif. Our RNA robot prototype opens the door to build more sophisticated RNA machines that use sensing, computing, and acting modules to precisely control RNA functionalities.

bioengineering↗

bioRxiv2023

Tertiary structure of single-instant RNA molecule reveals folding landscape

The folding of RNA and protein molecules during their synthesis is a crucial self-assembly process that nature employs to convert genetic information into the complex molecular machinery that supports life. Misfolding events are the cause of several diseases, and the folding pathway of central biomolecules, such as the ribosome, is strictly regulated by programmed maturation processes and folding chaperones. However, the dynamic folding processes are challenging to study because current structure determination methods heavily rely on averaging, and existing computational methods do not efficiently simulate non-equilibrium dynamics. Here we utilize individual-particle cryo-electron tomography (IPET) to investigate the folding landscape of a rationally designed RNA origami 6-helix bundle that undergoes slow maturation from a "young" to "mature" conformation. By optimizing the IPET imaging and electron dose conditions, we obtain 3D reconstructions of 120 individual particles at resolutions ranging from 23-35 [A], enabling us first-time to observe individual RNA helices and tertiary structures without averaging. Statistical analysis of 120 tertiary structures confirms the two main conformations and suggests a possible folding pathway driven by helix-helix compaction. Studies of the full conformational landscape reveal both trapped states, misfolded states, intermediate states, and fully compacted states. The study provides novel insight into RNA folding pathways and paves the way for future studies of the energy landscape of molecular machines and self-assembly processes.

biochemistry↗

bioRxiv2022

RNA origami scaffolds as a cryo-EM tool for investigating aptamer-ligand binding of a Broccoli-Pepper FRET pair

RNA nanotechnology uses motifs from nature as well as aptamers from in vitro selection to construct nanostructures and devices for applications in RNA medicine and synthetic biology. The RNA origami method allows cotranscriptional folding of large RNA scaffolds that can position functional motifs in a precise manner, which has been verified by Forster Resonance Energy Transfer (FRET) between fluorescent aptamers. Cryogenic electron microscopy (cryo-EM) is a promising method for characterizing the structure of larger RNA nanostructures. However, the structure of individual aptamers is difficult to solve by cryo-EM due to their low molecular weight. Here, we place aptamers on the RNA origami scaffolds to increase the contrast for cryo-EM and solve the structure of a new Broccoli-Pepper FRET pair. We identify different modes of ligand binding of the two aptamers and verify by selective probing. 3D variability analysis of the cryo-EM data show that the relative position between the two bound fluorophores on the origami fluctuate by only 3.5 Angstrom. Our results demonstrate the use of RNA origami scaffolds for characterizing small RNA motifs by cryo-EM and for positioning functional RNA motifs with high spatial precision. The Broccoli-Pepper apta-FRET pair has potential use for developing advanced sensors that are sensitive to small conformational changes.

biochemistry↗

bioRxiv2022

Cryo-EM structure and functional landscape of an RNA polymerase ribozyme

The emergence of an RNA replicase capable of self-replication is considered an important stage in the origin of life. RNA polymerase ribozymes (PR) including a variant that uses trinucleotide triphosphates (triplets) as substrates have been created by in vitro evolution and are the closest functional analogues of the replicase but the structural basis for their function is poorly understood. Here, we leverage single-particle cryo-EM and high-throughput mutation analysis to obtain the structure of a triplet polymerase ribozyme (TPR) apoenzyme and map its functional landscape. The TPR cryo-EM structure at 5-[A] resolution reveals an RNA heterodimer comprising a catalytic and an inactive accessory subunit, where the complex resembles a left hand with thumb and fingers at a 70{degrees} angle. The two subunits are connected by two distinct kissing-loop (KL) interactions that are essential for polymerase function. Our combined structural and functional data suggest a model for templated RNA synthesis by the TPR holoenzyme whereby heterodimer formation and KL interactions preorganize the TPR for optimal template binding and templated RNA synthesis activity. These results provide a foundation for a better understanding RNAs potential for self-replication.

biochemistry↗

bioRxiv2019

An RNA guanine quadruplex regulated pathway to TRAIL-sensitization by DDX21

DDX21 is a newly discovered RNA G-quadruplex (rG4) binding protein with no known biological rG4 targets. In this study we identified 26 proteins that are expressed at significantly different levels in cells expressing wild type DDX21 relative to an rG4 binding deficient DDX21 (M4). From this list we validate MAGED2 as a protein that is regulated by DDX21 through rG4 in its 5UTR. MAGED2 protein levels, but not mRNA levels, are reduced by half in cells expressing only DDX21 M4. MAGED2 has a repressive effect on TRAIL-R2 expression that is relieved under these conditions, resulting in elevated TRAIL-R2 mRNA and protein in cells expressing only DDX21 M4, and rendering previously resistant cells sensitive to TRAIL mediated apoptosis. Our work identifies the role of DDX21 in regulation at the translational level through biologically relevant rG4 and shows that MAGED2 protein levels are regulated, at least in part, by a rG4 forming potential in their 5UTRs.

biochemistry↗