Biology subjects

Montabana, E.

Publications and source records attributed to Montabana, E..

8 recordsLinked to original sources

bioRxiv2026

A Crossed Laser Phase Plate for CryoEM

The laser phase plate (LPP) enables phase-contrast imaging in cryogenic electron microscopy (cryoEM), enhancing image contrast without compromising high-resolution information. Here we report the implementation of a crossed laser phase plate (xLPP) comprising two optical cavities oriented orthogonally, installed in a ThermoFisher Scientific Krios G4 microscope equipped with a newly designed transfer lens module. We demonstrate the expected, strong contrast enhancement and stable, additive phase shifts of 90{degrees}, with a contrast transfer function (CTF) that closely matches theory. Single-particle analysis (SPA) of apoferritin, a standard benchmark sample, reached a resolution of 1.79 [A], demonstrating the system is capable of acquiring high-resolution cryoEM data. When imaging thick E. coli cells ([~]350 nm), the xLPP enhances contrast and increases low-frequency template-matching signal. Together, these results establish the feasibility of the xLPP and highlight its potential for high-contrast, high-resolution cryoEM imaging of biological systems.

biophysics↗

bioRxiv2026

Language Modeling Materializes a World Model of Protein Biology

Proteins are fundamental to life. The full extent of their biology is beyond our ability to characterize with experimental approaches in the physical laboratory. Accurate digital representations could accelerate the discovery of protein biology through virtual experiments. We propose language modeling to learn unified and general representations that can be scaled to all of protein biology. Building on these representations, we develop a structure prediction model that exceeds the performance of established methods for biomolecular complex prediction across benchmarks, including for the interactions of antibodies with their targets. A simple search procedure yields high experimental success rates for the discovery of proteins with nanomolar binding affinities for both miniproteins and single-chain antibodies, a modality critical for therapeutic design. Study of the concepts in the language models representation space reveals a systematic organization aligned with the reductionist understanding of proteins developed through empirical science. Leveraging this organization, we generate a comprehensive map of protein biology encompassing over 6.8 billion sequences and 1.1 billion predicted structures, identifying connections across known and unknown biology. As a whole, this shows language modeling as a powerful substrate for representing the biology of proteins, operating across scales from the prediction and design of protein interactions at the atomic level, to identifying properties of proteins at different levels of granularity and abstraction, to the scale of mapping connections between proteins across billions of years of evolution.

bioinformatics↗

bioRxiv2024

Annotating CryoET Volumes: A Machine Learning Challenge

Cryo-electron tomography (cryoET) has emerged as a powerful structural biology tool for understanding protein complexes in their native cellular environments. Presently, 3D volumes of cellular environments can be acquired in the thousands in a few days where each volume provides a rich and complex cellular landscape. Despite numerous innovations, localizing and identifying the vast majority of protein species in these volumes remains prohibitively difficult. Machine learning based methods provide an opportunity to automate the process of labeling and annotating cryoET volumes. Due to current bottlenecks in the annotation process, and a lack of large standardized datasets, training datasets for machine learning algorithms have been scarce. Here, we present a defined "phantom" sample, along with "ground truth" annotations, that will be the basis of a machine learning challenge to bring cryoET and ML experts together and spur creativity to address this annotation problem. We have also set up a cryoET data portal that provides additional diverse sets of annotated 3D volumes from cryoET experts across the world for the machine learning challenge.

cell biology↗

bioRxiv2024

Sec18 side-loading is essential for universal SNARE recycling across cellular contexts

SNARE proteins drive membrane fusion at different cell compartments as their core domains zipper into a parallel four-helix bundle. After fusion, these bundles are disassembled by the AAA+ protein Sec18/NSF and its adaptor Sec17/-SNAP to make them available for subsequent rounds of membrane fusion. SNARE domains are often flanked by C-terminal transmembrane or N-terminal domains. Previous structures of the NSF--SNAP-SNARE complex revealed binding to the D1 ATPase pore, posing a topological constraint as SNARE transmembrane domains would prevent complete substrate threading as suggested for other AAA+ systems. Using mass-spectrometry in yeast cells, we show N-terminal SNARE domain interactions with Sec18, exacerbating this topological issue. We present cryo-EM structures of a yeast SNARE complex, Sec18, and Sec17 in a non-hydrolyzing condition, which show SNARE Sso1 threaded through the D1 and D2 ATPase rings of Sec18, with its folded, N-terminal Habc domain interacting with the D2 ring. This domain does not unfold during Sec18/NSF activity. Cryo-EM structures under hydrolyzing conditions revealed substrate-released and substrate-free states of Sec18 with a coordinated opening in the side of the ATPase rings. Thus, Sec18/NSF operates by substrate side-loading and unloading topologically constrained SNARE substrates.

biophysics↗

bioRxiv2023

Step-wise activation of a Family C GPCR

Metabotropic glutamate receptors belong to a family of G protein-coupled receptors that are obligate dimers and possess a large extracellular ligand-binding domain (ECD) that is linked via a cysteine-rich domain (CRDs) to their 7-transmembrane (TM) domain. Upon activation, these receptors undergo a large conformational change to transmit the ligand binding signal from the ECD to the G protein-coupling TM. In this manuscript, we propose a model for a sequential, multistep activation mechanism of metabotropic glutamate receptor subtype 5. We present a series of structures in lipid nanodiscs, from inactive to fully active, including agonist-bound intermediate states. Further, using bulk and single-molecule fluorescence imaging we reveal distinct receptor conformations upon allosteric modulator and G protein binding.

biophysics↗

bioRxiv2022

Negative allosteric modulation of the glucagon receptor by RAMP2

Receptor activity-modifying proteins (RAMPs) modulate the activity of many Family B heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs). The glucagon receptor (GCGR), a Family B GPCR responsible for maintenance of proper blood sugar levels, interacts with RAMP2, though the purpose and consequence of this interaction is poorly understood. Using a series of biochemical and cell-based assays, we show that RAMP2 interacts with and broadly inhibits GCGR-induced downstream signaling. Hydrogen-deuterium exchange monitored by mass spectrometry (HDX-MS) demonstrates that RAMP2 enhances local flexibility in select locations in and near the receptor extracellular domain (ECD) as well as at a key region in the 6th transmembrane helix, while single-molecule fluorescence resonance energy transfer (smFRET) experiments show that this RAMP2-induced ECD disorder results in inhibition of active and intermediate states of the intracellular face of the receptor. Using cryo-electron microscopy (cryoEM), we determined the structure of the GCGR-Gs complex at 2.9 [A] resolution in the presence of RAMP2. RAMP2 apparently does not interact with GCGR in an ordered manner, yet the ECD of GCGR is indeed largely disordered in the presence of RAMP2. This disorder is accompanied by rearrangements of several key areas of the receptor, resulting in the formation of a likely unproductive complex. Together, our studies suggest that RAMP2 acts as a negative allosteric modulator of GCGR by enhancing conformational sampling of the ECD.

biochemistry↗

bioRxiv2021

eIF5B and eIF1A remodel human translation initiation complexes to mediate ribosomal subunit joining

Joining of the ribosomal subunits at a translation start site on a messenger RNA during initiation commits the ribosome to synthesize a protein. Here, we combined single-molecule spectroscopy and structural methods using an in vitro reconstituted system to examine how the human ribosomal subunits join. Single-molecule fluorescence revealed when universally-conserved eukaryotic initiation factors (eIFs) eIF1A and eIF5B associate with and depart from initiation complexes. Guided by single-molecule dynamics, we examined initiation complexes that contained both eIF1A and eIF5B using single-particle electron cryo-microscopy. The resulting structure illuminated how eukaryote-specific contacts between eIF1A and eIF5B remodel the initiation complex to orient initiator tRNA in a conformation compatible with ribosomal subunit joining. Collectively, our findings provide a quantitative and architectural framework for the molecular choreography orchestrated by eIF1A and eIF5B during human translation initiation.

biophysics↗

bioRxiv2018

Structural basis for selective stalling of human ribosome nascent chain complexes by a drug-like molecule

Small molecules that target the ribosome generally have a global impact on protein synthesis. However, the drug-like molecule PF-06446846 (PF846) binds the human ribosome and selectively blocks the translation of a small subset of proteins by an unknown mechanism. In high-resolution cryo-electron microscopy (cryo-EM) structures of human ribosome nascent chain complexes stalled by PF846, PF846 binds in the ribosome exit tunnel in a newly-identified and eukaryotic-specific pocket formed by the 28S ribosomal RNA (rRNA), and redirects the path of the nascent polypeptide chain. PF846 arrests the translating ribosome in the rotated state that precedes mRNA and tRNA translocation, with peptidyl-tRNA occupying a mixture of A/A and hybrid A/P sites, in which the tRNA 3-CCA end is improperly docked in the peptidyl transferase center. Using mRNA libraries, selections of PF846-dependent translation elongation stalling sequences reveal sequence preferences near the peptidyl transferase center, and uncover a newly-identified mechanism by which PF846 selectively blocks translation termination. These results illuminate how a small molecule selectively stalls the translation of the human ribosome, and provides a structural foundation for developing small molecules that inhibit the production of proteins of therapeutic interest.

biophysics↗