6 Oct 2022

A broad and potent neutralization epitope in SARS-related coronaviruses (PNAS)

Since the beginning of the COVID-19 pandemic, many severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants have emerged that are resistant to varying extents to neutralizing antibody responses induced by current vaccines and natural infection, especially the recent Omicron variants. Neutralizing potency and breadth for an antibody are often somewhat mutually exclusive. Here, we delineate the molecular interaction between a therapeutic antibody (ADG20) and SARS-CoV-2 receptor-binding domain (RBD) by X-ray crystallography and characterize its binding epitope. We show that this site is targeted by a few rare antibodies that have both potency and breadth. These findings provide insights into the design of more universal vaccines and broad therapeutic antibodies, which are pressingly needed.

6 Oct 2022

SARS-CoV-2 Delta and Omicron variants evade population antibody response by mutations in a single spike epitope (Nature Microbiology)

Population antibody response is thought to be important in selection of virus variants. We report that SARS-CoV-2 infection elicits a population immune response that is mediated by a lineage of VH1-69 germline antibodies. A representative antibody R1-32 from this lineage was isolated. By cryo-EM, we show that it targets a semi-cryptic epitope in the spike receptor-binding domain. Binding to this non-ACE2 competing epitope results in spike destruction, thereby inhibiting virus entry. On the basis of epitope location, neutralization mechanism and analysis of antibody binding to spike variants, we propose that recurrent substitutions at 452 and 490 are associated with immune evasion of the identified population antibody response. These substitutions, including L452R (present in the Delta variant), disrupt interactions mediated by the VH1-69-specific hydrophobic HCDR2 to impair antibody-antigen association, enabling variants to escape. The first Omicron variants were sensitive to antibody R1-32 but subvariants that harbour L452R quickly emerged and spread. Our results provide insights into how SARS-CoV-2 variants emerge and evade host immune responses.

6 Oct 2022

Posttranslational modifications optimize the ability of SARS-CoV-2 spike for effective interaction with host cell receptors (PNAS)

SARS-CoV-2 spike protein, which forms the basis for high pathogenicity and transmissibility of the virus, is a prime target for the development of both diagnostics and vaccines for the debilitating disease caused by the virus. We present a full model of spike methodically crafted and used to study its atomic-level dynamics by multiple microsecond simulations. The results shed light on the impact of posttranslational modifications on the pathogenicity of the virus. We show how glycan–glycan and glycan–lipid interactions broaden the protein’s dynamical range and thereby, its effective interaction with the surface receptors on the host cell. Palmitoylation of the spike membrane domain, however, results in a unique deformation pattern that might prime the membrane for fusion.

26 Nov

Structural ubiquitin contributes to K48 linkage-specificity of the HECT ligase Tom1

Homologous to E6AP C-Terminus (HECT) ubiquitin ligases play key roles in essential pathways such as DNA repair, cell cycle control or protein quality control. Tom1 is one of five HECT ubiquitin E3 ligases encoded in the S. cerevisiae genome and prototypical for a ligase with pleiotropic functions such as ubiquitin chain amplification, orphan quality control and DNA damage response. Structures of full-length HECT ligases, including the Tom1 ortholog HUWE1, have been reported, but how domains beyond the conserved catalytic module contribute to catalysis remains largely elusive. Here, through cryogenic electron microscopy (cryo-EM) of Tom1 during an active ubiquitylation cycle, we demonstrate that the extended domain architecture directly contributes to activity. We identify a Tom1-ubiquitin architecture during ubiquitylation involving a non-canonical ubiquitin binding site in the solenoid shape of Tom1. We demonstrate that this ubiquitin binding site coordinates a structural ubiquitin contributing to the fidelity of K48 poly-ubiquitin chain assembly.​

26 Nov

Large-Scale Quantitative Cross-Linking and Mass Spectrometry Provides New Insight on Protein Conformational Plasticity within Organelles, Cells, and Tissues (Biorxiv)

Many proteins can exist in multiple conformational states in vivo to achieve distinct functional roles. These states include alternative conformations, variable PTMs, and association with interacting protein, nucleotide, and ligand partners. Quantitative chemical cross-linking of live cells, organelles, or tissues together with mass spectrometry provides the relative abundance of cross-link levels formed in two or more compared samples, which depends both on the relative levels of existent protein conformational states in the compared samples as well as the relative likelihood of the cross-link originating from each. Because cross-link conformational state preferences can vary widely, one expects intra-protein cross-link levels from proteins with high conformational plasticity to display divergent quantitation among samples with differing conformational ensembles. Here we use the large volume of quantitative cross-linking data available on the public XLinkDB database to cluster intra-protein cross-links according to their quantitation in many diverse compared samples to provide the first widescale glimpse of cross-links grouped according to the protein conformational state(s) from which they predominantly originate. We further demonstrate how cluster cross-links can be aligned with any protein structure to assess the likelihood that they were derived from it.​

25 Nov

Improved automated model building for cryo-EM maps using CryFold (Biorxiv)

Constructing atomic models from cryogenic electron microscopy (cryo-EM) density maps is essential for interpreting molecular mechanisms. In this study, we present CryFold, an approach for de novo model building in cryo-EM that leverages recent advancements in AlphaFold2 to improve the state-of-the-art method ModelAngelo. To incorporate the cryo-EM map information, CryFold replaces the global attention mechanism in AlphaFold2 to local attention, further enhanced by a novel 3D rotary position embedding. It produces more complete models, accelerates the modeling, and reduces the resolution requirement. Applying CryFold to new maps results in accurate differentiation between paralog sequences in noisy regions, detection of previously uncharacterized proteins with unknown functions, precise compartmentalisation of the map for isolation of non-protein components, and improved modeling of conformational changes. In a particular case, a 104-protein complex was modeled within only 5.6 hours, and a minor conformational change of a single protein domain was detected at the periphery when models from two different maps were compared. CryFold stands as an accurate method currently available for model building of proteins in cryo-EM structure determination. CryFold is open-source software available at https://github.com/SBQ-1999/CryFold.​

7 Dec 2023

Celebrating 30 years of Structure

Journal Structure was launched in 1993 as the first journal exclusively dedicated to structural biology by our founding academic chief editors, Wayne A. Hendrickson and Carl-Ivar Br€ande´ n, who were later joined by Alan Fersht. Christopher Lima and Andrej Sali became academic chief editors of Structure in 2003, and they were at the helm of the journal for 18 years until stepping down in the autumn 2021.

Structure is now celebrating its 30th birthday with this special anniversary issue. Editors commissioned reviews to highlight recent developments in different areas of structural biology. Sabine Botha and Petra Fromme provide an overview of the current state of serial femtosecond crystallography (SFX) research, the impact COVID-19 had on the SFX community, and how scientists adapted to these challenges. Koji Yonekura and his co-workers describe their contributions toward the development of electron 3D crystallography/microcrystal electron diffraction (MicroED) and highlight applications and current limitations of this method. Vaibhav KumarShukla, Gabriella Heller, and Flemming Hansen discuss the impact of artificial intelligence (AI) on biomolecular nuclear magnetic resonance (NMR) spectroscopy. Tuo Wang and his colleagues report how solid-state NMR is used to study the structures of fungaland plant cell walls. Syma Khalid and her co-workers define the term ‘‘computational microbiology’’ and describe state-of-the-art molecular dynamics imulations of bacterial systems.

21 Nov 2023

Soft-landing methods aim to simplify structural biology (Nature)

Linking mass spectrometry with cryo-electron microscopy could transform understanding of complex protein structures — if scientists can show that samples remain intact when they hit their target. In his lecture after winning a share of the 2002 Nobel Prize in Chemistry, John Fenn described his work as creating “wings for molecular elephants”. Fenn pioneered the use of a method called electrospray ionization (ESI) to make intact proteins — among nature’s beefiest biomolecules — literally fly, transferring them from complex mixtures into gases and then into mass spectrometers for extensive analysis. Alongside the research of co-recipient Koichi Tanaka, Fenn’s work made it possible for scientists to dive deep into the chemical composition — and therefore the sequences, chemical modifications, and molecular partners — of whole proteins, using mass spectrometry.

21 Nov 2023

Identification of motif-based interactions between SARS-CoV-2 protein domains and human peptide ligands pinpoint antiviral targets (Nature Communications)

The virus life cycle depends on host-virus protein-protein interactions, which often involve a disordered protein region binding to a folded protein domain. Here, we used proteomic peptide phage display (ProP-PD) to identify peptides from the intrinsically disordered regions of the human proteome that bind to folded protein domains encoded by the SARS-CoV-2 genome. Eleven folded domains of SARS-CoV-2 proteins were found to bind 281 peptides from human proteins, and affinities of 31 interactions involving eight SARS-CoV-2 protein domains were determined (K_D ∼ 7-300 μM). Key specificity residues of the peptides were established for six of the interactions. Two of the peptides, binding Nsp9 and Nsp16, respectively, inhibited viral replication. Our findings demonstrate how high-throughput peptide binding screens simultaneously identify potential host-virus interactions and peptides with antiviral properties. Furthermore, the high number of low-affinity interactions suggests that overexpression of viral proteins during infection may perturb multiple cellular pathways.

21 Nov 2023

Intrinsic structural dynamics dictate enzymatic activity and inhibition (PNAS)

Enzymes are known to sample various conformations, many of which are critical for their biological function. However, structural characterizations of enzymes predominantly focus on the most populated conformation. As a result, single-point mutations often produce structures that are similar or essentially identical to those of the wild-type enzyme despite large changes in enzymatic activity. Here, we show for mutants of a histone deacetylase enzyme (HDAC8) that reduced enzymatic activities, reduced inhibitor affinities, and reduced residence times are all captured by the rate constants between intrinsically sampled conformations that, in turn, can be obtained independently by solution NMR spectroscopy. Thus, for the HDAC8 enzyme, the dynamic sampling of conformations dictates both enzymatic activity and inhibitor potency. Our analysis also dissects the functional role of the conformations sampled, where specific conformations distinct from those in available structures are responsible for substrate and inhibitor binding, catalysis, and product dissociation. Precise structures alone often do not adequately explain the effect of missense mutations on enzymatic activity and drug potency. Our findings not only assign functional roles to several conformational states of HDAC8 but they also underscore the paramount role of dynamics, which will have general implications for characterizing missense mutations and designing inhibitors.

21 Nov 2023

Streamlined structure determination by cryo-electron tomography and subtomogram averaging using TomoBEAR (Nature Communications)

Structures of macromolecules in their native state provide unique unambiguous insights into their functions. Cryo-electron tomography combined with subtomogram averaging demonstrated the power to solve such structures in situ at resolutions in the range of 3 Angstrom for some macromolecules. In order to be applicable to the structural determination of the majority of macromolecules observable in cells in limited amounts, processing of tomographic data has to be performed in a high-throughput manner. Here we present TomoBEAR—a modular configurable workflow engine for streamlined processing of cryo-electron tomographic data for subtomogram averaging. TomoBEAR combines commonly used cryo-EM packages with reasonable presets to provide a transparent (“white box”) approach for data management and processing. We demonstrate applications of TomoBEAR to two data sets of purified macromolecular targets, to an ion channel RyR1 in a membrane, and the tomograms of plasma FIB-milled lamellae and demonstrate the ability to produce high-resolution structures. TomoBEAR speeds up data processing, minimizes human interventions, and will help accelerate the adoption of in situ structural biology by cryo-ET. The source code and the documentation are freely available.