Biology subjects

Lander, G. C.

Publications and source records attributed to Lander, G. C..

At least 19 recordsLinked to original sources

bioRxiv2026

Allosteric covalent inhibition of cereblon through cryptic cysteine targeting

Thalidomide-derived cereblon (CRBN) modulators are among the most clinically impactful targeted protein degradation therapeutics, redirecting the CRL4-CRBN E3 ubiquitin ligase to degrade disease-driving neosubstrates. All current CRBN-targeting IMiDs and CELMoDs engage a single orthosteric pocket, leaving CRBN's conformational landscape largely unexploited pharmacologically. Using cysteine-directed chemoproteomic screening, we identified covalent ligands that engage Cys287, a cryptic allosteric pocket distal to the orthosteric site. Our lead compound, VVD-105917, acts as a pan-inhibitor of IMiD/CELMoD-driven neosubstrate degradation. Cryo-EM structures reveal that covalent Cys287 engagement traps CRBN in its open, inactive conformation, resolving a previously unobserved N-terminal segment and sensor loop. Sequential incubation experiments show the conformational outcome depends on ligand addition order, demonstrating that even potent CELMoD-driven closure can be overridden by allosteric engagement. A recently reported ligand at this same pocket produces the opposite effect, promoting rather than blocking closure, indicating the Cys287 site is mechanistically sign-switchable. These findings establish covalent chemoproteomics as a strategy for discovering and controlling E3 ligase conformational switches.

biochemistry↗

bioRxiv2026

Structural Plasticity and Ligand Promiscuity of CYP3A4 Revealed by Cryo-EM

Cytochrome P450 3A4 (CYP3A4) metabolizes roughly half of all marketed drugs, and its inhibition can cause clinically significant drug-drug interactions. The enzyme accommodates chemically diverse ligands, making binding modes and metabolic outcomes difficult to predict. Previous X-ray crystallography efforts have leveraged a truncated construct without the N-terminal segment that tethers CYP3A4 to the membrane. Here we show that the same construct assembles into a symmetric trimer that can be resolved by cryo-EM and determine structures of both unliganded and ligand-bound CYP3A4. Multiple ligands are resolved with density consistent with several mutually exclusive conformations. Protein remodeling to reshape the binding pocket is concentrated in the F/G loop, which is poorly resolved and unmodeled in many X-ray structures. These features likely underlie the poor predictive performance of co-folding methods on this target. The routine use of cryo-EM to resolve CYP3A4 ligand-bound complexes will provide the ground truth data needed to make predictive models of drug metabolism useful in practice.

biophysics↗

bioRxiv2026

From Hummingbird to Elephant: Amyloid Formation in Natural Transthyretin Variants

Transthyretin (TTR) is a secreted protein associated with cardiac and other amyloid diseases via misfolding. We have previously shown that agitation of human TTR solutions at neutral pH results in aggregation and fibril formation. Here we report that agitation-induced aggregation of TTR from species with very different heart rates (Annas hummingbird, hbTTR, and African elephant, aeTTR) differs from that of human TTR (huTTR). Aggregation of hbTTR is slow and favors formation of smaller, fibrillar aggregates, while aeTTR aggregation is rapid and favors larger, more amorphous particles. Spherical, early-stage oligomeric intermediates were found for all variants by mass photometry and electron microscopy. The slow aggregation of hbTTR matches its resistance to denaturation by 8 M urea. The widely different aggregation behavior exhibited by these naturally occurring TTR variants in response to mechanical agitation under close to physiological conditions provides insight into how small sequence differences can contribute to the evolutionary fitness of different animals.

biophysics↗

bioRxiv2026

Siphoviridae phage tails co-enrich with ex vivo amyloids

Amyloid fibrils extracted from patient tissue are enriched by physicochemical fractionation methods and enzymatic tissue digestion with collagenase, resulting in a mixture of sedimented complexes. Reprocessing of an ex vivo lysozyme amyloid dataset revealed non-amyloid tubular assemblies, which we reconstructed to 3.5 angstrom. Sequence-agnostic model building with CryoAtom and fold search with FoldSeek identified a phage tail tube fold. Testing the crude Clostridium histolyticum collagenase used for tissue digestion, negative-stain TEM and LC-MS/MS showed proteins of an F-type tailocin, allowing us to assign the helical reconstruction to a major tail tube protein (TTP) of C. histolyticum. We also observed tailocin contamination in cardiac light-chain amyloid extracts, following the same collagenase treatment. Overall, we identify tailocins as recurrent reagent-borne contaminants in collagenase-treated ex vivo amyloid preparations and propose strategies to detect and avoid such artefacts in single-particle cryo-EM by optimizing the experimental design and data annotation towards a database of common contaminants.

biophysics↗

bioRxiv2026

DM: a simple solution to suppress air-water interface interactions in cryo-EM

The air-water interface (AWI) remains the primary barrier to routine high-resolution cryo-EM structure determination, driving protein adsorption, structural denaturation, and restricted particle orientations during vitrification. Here, we describe a simple and broadly applicable strategy to mitigate these effects using the mild non-ionic detergent n-decyl-{beta}-D-maltopyranoside (DM). Addition of DM at low millimolar concentrations immediately prior to vitrification consistently suppresses AWI-driven artifacts, resulting in improved angular sampling, reduced structural damage, and enhanced reconstruction quality across diverse macromolecular systems. Using this approach, we obtained a high-resolution reconstruction of the 65 kDa Nucleophosmin 1 pentamer, a target previously limited by severe preferred orientation issues. We further show that DM promotes isotropic particle distributions for high-resolution reconstruction of hemagglutinin, transthyretin, as well as suppressing denaturation of aldolase while stabilizing its C-terminus. Our results indicate that DM effectively passivates deleterious air-water interface interactions without compromising particle integrity. These results establish DM as an effective additive for improving the robustness of single-particle cryo-EM sample preparation. O_FIG O_LINKSMALLFIG WIDTH=174 HEIGHT=200 SRC="FIGDIR/small/716008v1_ufig1.gif" ALT="Figure 1"> View larger version (56K): org.highwire.dtl.DTLVardef@108a6edorg.highwire.dtl.DTLVardef@10728b4org.highwire.dtl.DTLVardef@1014b2eorg.highwire.dtl.DTLVardef@1eed745_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2026

Pharmacological Inhibition of SLC33A1 Promotes Endoplasmic Reticulum Hyperoxidation and Induces Adaptive IRE1/XBP1s Signaling

The endoplasmic reticulum (ER) transporter solute carrier family 33 member 1 (SLC33A1) has emerged as an attractive therapeutic target in etiologically diverse diseases, ranging from lung cancer to neurodegenerative disorders. Yet, no pharmacologic SLC33A1 modulators have been described. Here, we show that the small molecule IXA4, a highly selective activator of the adaptive IRE1/XBP1s signaling arm of the unfolded protein response (UPR), binds to SLC33A1 and inhibits its activity. Genetic depletion of SLC33A1 phenocopies the selective induction of IRE1/XBP1s signaling brought about by IXA4 treatment. Chemoproteomic analyses and cryo-electron microscopy show that IXA4 binds SLC33A1 within the central channel to inhibit transport of its substrate metabolite(s). Binding of IXA4 to SLC33A1 leads to the accumulation of oxidized glutathione within the ER, hyperoxidizing the ER lumen and inducing activation of adaptive IRE1/XBP1s signaling. Consistent with this function, we find that pharmacologic inhibition of SLC33A1 with IXA4 selectively reduces viability of KEAP1-deficient lung adenocarcinoma cells that have elevated levels of glutathione, mimicking the sensitivity of these cells to genetic deletion of SLC33A1. Our work demonstrates a new physiologic role of SLC33A1 in regulation of ER redox homeostasis and designates IXA4 as a pharmacologic inhibitor of SLC33A1 that can be used to evaluate the biological impact and therapeutic utility of SLC33A1 inhibition in homeostasis and in disease.

cell biology↗

bioRxiv2026

3D Visualization and Proteomic Analysis of Human Cardiac Transthyretin Amyloidosis Tissue Reveals Microangiopathy and Capillary Occlusion

AO_SCPLOWBSTRACTC_SCPLOWO_ST_ABSBackgroundC_ST_ABSTransthyretin amyloidosis (ATTR) is a progressive, degenerative disease affecting the heart and other organ systems, as well as the peripheral, autonomic, and central nervous systems. Although pharmacological and genetic evidence establishes aggregation as a driver of ATTR pathology, the mechanism by which aggregation compromises post-mitotic tissue function is poorly understood. We utilized bottom-up proteomics on wild-type (WT) human cardiac (WT/WT genotype) and V122I human cardiac (V122I/WT genotype) tissue, combined with tissue clearing technology to create an optically transparent tissue architecture to visualize three-dimensional relationships, to better understand TTR cardiomyopathy (CM). MethodsFlash-frozen 0.5 mm cardiac tissue slices from human subjects with end-stage WT-TTR CM, end-stage V122I CM, and slices from an age-matched human control were used for these experiments. Fibril extraction from diseased tissue followed published protocols. Strong denaturant-mediated proteome tissue extraction on samples from each subject facilitated bottom-up proteomics by using liquid chromatography (LC)-mass spectrometry (MS)/MS. Tissue clearing was performed on 0.5 mm cardiac slices utilizing a lauryl sulfate-based lipid removal strategy. Slices were stained using indirect immunofluorescence with antibodies to protein targets identified by proteomics. We used an antibody to non-native TTR and AmyTracker 480 (an oligothiophene dye that binds to amyloid fibrils) to image TTR deposits. ATTR fibrils were characterized structurally using cryogenic electron microscopy (cryo-EM) followed by helical reconstruction. ResultsProteomic cardiac analysis afforded high spectral counts for transthyretin (TTR) and proteins typically associated with amyloid fibrils, e.g. serum amyloid P (APCS). Fibril and cardiac homogenate proteomics revealed high levels of angiogenic and hemostatic proteins, including those composing the complement and coagulation cascades. 3D imaging revealed loss of normal microvascular architecture in CM samples with regions of hyper- and hypovascularization. Microvascular obstruction by capillary thrombosis was also observed in CM. ATTR fibrils adopted the common spearhead fold and were decorated with collagen VI (COLVI), an extracellular matrix component. ConclusionsWe hypothesize that ATTR CM is a microangiopathy driven by capillary bed thrombo-inflammation and dysregulated angiogenic revascularization. Phenotypic convergence of WT ATTR CM and V122I ATTR CM was observed via proteomics, 3D imaging, and ex vivo fibril characterization by cryo-EM. We provide evidence of capillary thrombosis in ex vivo ATTR CM tissue. Vasodilation and increased capillary permeability expose components of the vascular basement membrane (VBM) to misfolded TTR. These components are known to promote TTR aggregation and stabilize amyloid fibrils in the extracellular space. Congestion of the VBM prevents appropriate revascularization, reducing cardiac exertional capacity over time, leading to heart failure. Our ATTR CM heart tissue proteomics data shows significant overlap with the proteomic profiles of human AD brain tissues, revealing key amyloid, coagulation, complement, and angiogenesis proteins being changed in amyloidoses.

pathology↗

bioRxiv2025

Helical Reconstruction of Amyloids in cryoSPARC

Amyloid-mediated proteotoxicity underlies more than 50 human diseases. Cryo-electron microscopy (cryo-EM) analyses have yielded hundreds of in vitro and patient-derived amyloid structures, establishing direct links between filament morphologies and specific pathological conditions. Despite the growing popularity of the processing software cryoSPARC for single-particle analyses, RELION remains the dominant software platform for performing helical reconstruction of amyloid structures, highlighting an area for further development. Here, we present comprehensive processing guidelines for helical reconstruction of helical amyloids using cryoSPARC. Through systematic re-processing and validation of publicly deposited datasets, we demonstrate current capabilities and identify key limitations, emphasizing the need for amyloid-specific parameter optimization within cryoSPARC workflows. Our findings showcase a potential for developing unsupervised processing workflows to meet the demanding throughput requirements of time-resolved in vitro studies and largescale compound screening initiatives, thereby accelerating therapeutic drug development. Ultimately, our goal is to shift the focus of amyloid cryo-EM from computationally intensive processing challenges toward addressing fundamental biological questions that enhance our capacity for treatment discovery. O_FIG O_LINKSMALLFIG WIDTH=110 HEIGHT=200 SRC="FIGDIR/small/680389v2_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@1f2e9fcorg.highwire.dtl.DTLVardef@dfb6f5org.highwire.dtl.DTLVardef@164a2c3org.highwire.dtl.DTLVardef@1f9c570_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioinformatics↗

bioRxiv2025

Human SerRS/SIRT2 complex structure reveals cross regulation between translation and NAD+ metabolism

Life at the cellular level depends on effective coordination between diverse processes. Here we uncover a novel cross-regulation between metabolism and translation through a 3.2 [A] cryo-EM structure of human cytosolic seryl-tRNA synthetase (SerRS) bound to sirtuin-2 (SIRT2), an NAD+-dependent deacetylase. This interaction, naturally triggered by the NAD+ metabolite ADP-ribose (ADPR), resembles substrate binding and block SIRT2s active site. Interestingly, SerRS acetylation is not required for this interaction. SIRT2 binding sterically and allosterically impedes tRNA binding to SerRS, lowering charged tRNASer level and protein synthesis activity. Key interaction residues in both proteins emerged simultaneously in vertebrates, suggesting co-evolution for cross-regulation. Given ADPRs accumulation under stress, the ADPR-induced SerRS/SIRT2 interaction likely serves as a cell-protective response.

molecular biology↗

bioRxiv2025

Cryo-EM Reveals Regulatory Mechanisms Governing Substrate Selection and Activation of Human LONP1

The human AAA+ protease LONP1 plays a central role in maintaining mitochondrial proteostasis. LONP1 processes a vast array of substrates, ranging from damaged or unfolded proteins to specific subunits stably integrated into respiratory complexes. Previous cryo-EM studies of LONP1 uncovered two distinct conformational states corresponding to inactive or active forms of the enzyme. While these states have shed light on the intricacies of LONP1 substrate translocation and proteolytic processing, little is known about the decision-making involved in LONP1 substrate engagement and subsequent initiation of its unfoldase activity. Here, we use cryo-EM to determine a novel ADP-bound, C3-symmetric intermediate state of LONP1 (LONP1C3) with putative substrate "fold-sensing" capabilities. Our biochemical and structural data indicate that LONP1C3 is an on-pathway intermediate and that is stabilized by interaction with folded substrates. Moreover, we identify additional symmetric and asymmetric conformational states, including a two-fold symmetric split-hexamer conformation, that we associate with the transition from LONP1C3 to LONP1ENZ. We propose that the C3-state regulates substrate selection and enables LONP1 to efficiently surveil the matrix proteome to ensure selective removal of damaged and dysfunctional proteins as well as privileged LONP1 substrates. These findings collectively provide further mechanistic insights into LONP1 substrate recruitment and engagement and inform on its diverse roles in maintaining homeostasis within the mitochondria.

molecular biology↗

bioRxiv2025

Mix-it-up: Accessible time-resolved cryo-EM on the millisecond timescale

Biological reactions often involve macromolecules that undergo substrate-induced conformational changes in under a second, yet capturing these transient states remains challenging. While high-resolution structural techniques such as X-ray crystallography and cryo-electron microscopy (cryo-EM) have advanced our mechanistic understanding of protein-substrate interactions, traditional sample preparation methods are too slow to capture rapid biochemical events. Time-resolved cryo-EM has emerged as a promising approach to visualize structural dynamics on microsecond-to-millisecond timescales, but its widespread adoption has been limited by costly equipment and challenges in achieving rapid mixing, application, and vitrification of samples in a reproducible manner. To address these limitations, we developed "Mix-it-up" (MIU), a modified spray device designed for rapid on-grid mixing and vitrification of cryo-EM samples. By manually applying one sample onto the EM grid, blotting, and subsequently spraying the second sample, we achieve on-grid mixing with a vitrification delay of as low as ~120 milliseconds. We demonstrate MIUs time-resolved capabilities through high-resolution structure determination of mixed samples, pH-induced viral capsid contraction, and ligand-dependent complex formation. These findings establish MIU as a cost-effective, versatile tool for studying rapid biochemical processes and lay the groundwork for future applications to time-resolved cryo-EM.

molecular biology↗

bioRxiv2025

Magellon - an extensible platform for cryo-EM data visualization, management, and processing

Single particle cryo-electron microscopy (cryo-EM) has revolutionized structural biology by enabling high-resolution determination of macromolecular structures. However, the field faces challenges in data management, processing workflow integration, and software extensibility. We present Magellon, an innovative cryo-EM software platform that addresses these challenges through a modern microservices architecture. Magellon consists of an extensible backend with a web-based front end that we call Magellon Viewer. Together, these combine high-performance computing capabilities with an intuitive user interface, enabling researchers to efficiently process and analyze cryo-EM data. The platforms distinguishing features include a plugin-based architecture, distributed processing capabilities, comprehensive monitoring systems, and a novel approach to data organization and visualization. A key philosophy of the approach is that the Magellon backend provides a platform that uses robust industry-standard libraries to orchestrate computational tasks while offering users and developers flexibility in selecting the computational resources for performing calculations. Magellon represents a significant advancement in cryo-EM software infrastructure, offering flexibility, scalability, and extensibility while maintaining ease of use.

biophysics↗

bioRxiv2024

Cellular Function of a Biomolecular Condensate Is Determined by Its Ultrastructure

Biomolecular condensates play key roles in the spatiotemporal regulation of cellular processes. Yet, the relationship between atomic features and condensate function remains poorly understood. We studied this relationship using the polar organizing protein Z (PopZ) as a model system, revealing how its material properties and cellular function depend on its ultrastructure. We revealed PopZs hierarchical assembly into a filamentous condensate by integrating cryo-electron tomography, biochemistry, single-molecule techniques, and molecular dynamics simulations. The helical domain drives filamentation and condensation, while the disordered domain inhibits them. Phase-dependent conformational changes prevent interfilament contacts in the dilute phase and expose client binding sites in the dense phase. These findings establish a multiscale framework that links molecular interactions and condensate ultrastructure to macroscopic material properties that drive cellular function.

cell biology↗

bioRxiv2024

Cryo-EM structures of human ClpXP reveal mechanisms of assembly and proteolytic activation

The human ClpXP complex (hClpXP) plays a central role in mitochondrial protein quality control by degrading misfolded or unneeded proteins. While bacterial ClpXP complexes have been extensively characterized, the molecular determinants underlying hClpXP assembly and regulation are not as well understood. We determined cryo-electron microscopy (cryo-EM) structures of hClpP in isolation and in complex with hClpX, revealing how hClpX binding promotes rearrangement of an asymmetric hClpP heptamer to assemble as a symmetric tetradecamer. Our hClpXP structure also highlights the stabilizing role of a previously uncharacterized eukaryotic ClpX sequence, referred to as the E-loop, and its importance in ATPase activity and hexamer assembly. We further show that peptide interaction with the hClpP proteolytic active site promotes the complex to adopt a proteolytically competent conformation. Together, these findings advance our understanding of the molecular mechanisms defining hClpXP activation and function.

molecular biology↗

bioRxiv2024

Sub-3 A resolution protein structure determination by single-particle cryo-EM at 100 keV

Cryo-electron microscopy (cryo-EM) has revolutionized structural biology by providing high-resolution insights into biological macromolecules. Here, we present sub-3 [A] resolution structures determined using the 100 keV Tundra cryogenic transmission electron microscope (cryo-TEM), equipped with the newly developed Falcon C direct electron detector (DED). Our results demonstrate that this lower voltage microscope, when combined with advanced electron optics and detectors, can achieve high-resolution reconstructions that were previously only attainable with higher voltage systems. The implementation of an extreme-brightness field emission gun (XFEG) and an SP-TWIN objective lens significantly enhanced the spatial and temporal coherence of the system. Furthermore, the semi-automated sample loader minimized contamination and drift, allowing extended data collection sessions without manual intervention. The high detective quantum efficiency (DQE) of Falcon C further improved the signal-to-noise ratio, which is critical for achieving high-resolution structures. We validated the performance of this microscope by determining the structures of various biological samples, including apoferritin, T20S proteasome, GABAA receptor, haemoglobin, and human transthyretin ranging in size from 440 kDa to 50 kDa. The highest resolutions achieved were 2.1 [A] for apoferritin, 2.7 [A] for the 20S proteasome, 2.8 [A] for the GABAA receptor, 5.0 [A] for haemoglobin, and 3.5 [A] for transthyretin. We also explored a larger specimen, a 3.9 MDa Adeno-associated virus (AAV9) capsid and resolved it a 2.8 [A]. This work highlights the potential of 100 keV TEMs to make high-resolution cryo-EM more accessible to the structural biology community. Furthermore, it sets a precedent for the use of lower voltage TEMs in routine cryo-EM studies, not only for screening grids for single particle analysis but also for achieving high-resolution structures of protein samples.

biophysics↗

bioRxiv2024

Structural and mechanistic studies on human LONP1 redefine the hand-over-hand translocation mechanism

AAA+ enzymes use energy from ATP hydrolysis to remodel diverse cellular targets. Structures of substrate-bound AAA+ complexes suggest that these enzymes employ a conserved hand-over-hand mechanism to thread substrates through their central pore. However, the fundamental aspects of the mechanisms governing motor function and substrate processing within specific AAA+ families remain unresolved. We used cryo-electron microscopy to structurally interrogate reaction intermediates from in vitro biochemical assays to inform the underlying regulatory mechanisms of the human mitochondrial AAA+ protease, LONP1. Our results demonstrate that substrate binding allosterically regulates proteolytic activity, and that LONP1 can adopt a configuration conducive to substrate translocation even when the ATPases are bound to ADP. These results challenge the conventional understanding of the hand-over-hand translocation mechanism, giving rise to an alternative model that aligns more closely with biochemical and biophysical data on related enzymes like ClpX, ClpA, the 26S proteasome, and Lon protease.

molecular biology↗

bioRxiv2024

Human polymerase theta helicase positions DNA microhomologies for double-strand break repair

DNA double-strand breaks occur in all human cells on a daily basis and must be repaired with high fidelity to minimize genomic instability1. Deficiencies in high-fidelity DNA repair by homologous recombination lead to dependence on DNA polymerase theta, which identifies DNA microhomologies in 3 single-stranded DNA overhangs and anneals them to initiate error-prone double-strand break repair. The resulting genomic instability is associated with numerous cancers, thereby making this polymerase an attractive therapeutic target2,3. However, despite the biomedical importance of polymerase theta, the molecular details of how it initiates DNA break repair remain unclear4,5. Here we present cryo-electron microscopy structures of the polymerase theta helicase domain bound to microhomology-containing DNA, revealing DNA-induced rearrangements of the helicase that enable DNA repair. Our structures show that DNA-bound helicase dimers facilitate a microhomology search that positions 3 single-stranded DNA ends in proximity to align complementary base pairs and anneal DNA microhomology. We define the molecular determinants that enable the polymerase theta helicase domain to identify and pair DNA microhomologies to initiate mutagenic DNA repair, providing mechanistic insights into therapeutic targeting of these interactions.

molecular biology↗

bioRxiv2024

High-resolution single particle imaging at 100-200 keV with the Gatan Alpine direct electron detector.

Developments in direct electron detector technology have played a pivotal role in enabling high-resolution structural studies by cryo-EM at 200 and 300 keV. Yet, theory and recent experiments indicate advantages to imaging at 100 keV, energies for which the current detectors have not been optimized. In this study, we evaluated the Gatan Alpine detector, designed for operation at 100 and 200 keV. Compared to the Gatan K3, Alpine demonstrated a significant DQE improvement at these voltages, specifically a ~4-fold improvement at Nyquist at 100 keV. In single-particle cryo-EM experiments, Alpine datasets yielded better than 2 [A] resolution reconstructions of apoferritin at 120 and 200 keV on a ThermoFisher Scientific (TFS) Glacios microscope. We also achieved a ~3.2 [A] resolution reconstruction for a 115 kDa asymmetric protein complex, proving its effectiveness with complex biological samples. In-depth analysis revealed that Alpine reconstructions are comparable to K3 reconstructions at 200 keV, and remarkably, reconstruction from Alpine at 120 keV on a TFS Glacios surpassed all but the 300 keV data from a TFS Titan Krios with GIF/K3. Additionally, we show Alpines capability for high-resolution data acquisition and screening on lower-end systems by obtaining ~3 [A] resolution reconstructions of apoferritin and aldolase at 100 keV and detailed 2D averages of a 55 kDa sample using a side-entry cryo holder. Overall, we show that Gatan Alpine performs well with the standard 200 keV imaging systems and may potentially capture the benefits of lower accelerating voltages, possibly bringing smaller sized particles within the scope of cryo-EM.

biophysics↗