Structural and molecular basis of choline uptake into the brain by FLVCR2.

Choline is an essential nutrient that the human body needs in vast quantities for cell membrane synthesis, epigenetic modification and neurotransmission. The brain has a particularly high demand for choline, but how it enters the brain remains unknown1-3. The major facilitator superfamily transporter FLVCR1 (also known as MFSD7B or SLC49A1) was recently determined to be a choline transporter but is not highly expressed at the blood-brain barrier, whereas the related protein FLVCR2 (also known as MFSD7C or SLC49A2) is expressed in endothelial cells at the blood-brain barrier4-7. Previous studies have shown that mutations in human Flvcr2 cause cerebral vascular abnormalities, hydrocephalus and embryonic lethality, but the physiological role of FLVCR2 is unknown4,5. Here we demonstrate both in vivo and in vitro that FLVCR2 is a BBB choline transporter and is responsible for the majority of choline uptake into the brain. We also determine the structures of choline-bound FLVCR2 in both inward-facing and outward-facing states using cryo-electron microscopy. These results reveal how the brain obtains choline and provide molecular-level insights into how FLVCR2 binds choline in an aromatic cage and mediates its uptake. Our work could provide a novel framework for the targeted delivery of therapeutic agents into the brain.

Seasonal Variability in the Prevalence of DWV Strains in Individual Colonies of European Honeybees in Hawaii.

The most prevalent viral pathogen of honeybees is Deformed Wing Virus (DWV) and its two most widely studied and common master-variants are DWV-A and DWV-B. The prevalence of DWV variants in the UK and in the US is changing, with the prevalence of the DWV-A strain declining and DWV-B increasing over time. In 2012, only DWV-A was detected on the Hawaiian Islands of Oahu. In this study we focused on a colony-level survey of DWV strains in a single apiary and examined the prevalence of DWV variants over the course of two years. In 2018 and 2019, a total of 16 colonies underwent viral testing in January, May, and September. Of those 16 colonies, four were monitored in both 2018 and 2019. Individual colonies showed variability of DWV master variants throughout the sampling period. DWV-A was consistently detected; however, the detection of DWV-B was variable across time in individual colonies. Ultimately, this study demonstrated a seasonal variation in both viral prevalence and load for DWV-B, providing a perspective on the dynamic nature of DWV master variants emerging in Hawaii.

Promiscuous G-protein activation by the calcium-sensing receptor.

The human calcium-sensing receptor (CaSR) detects fluctuations in the extracellular Ca2+ concentration and maintains Ca2+ homeostasis1,2. It also mediates diverse cellular processes not associated with Ca2+ balance3-5. The functional pleiotropy of CaSR arises in part from its ability to signal through several G-protein subtypes6. We determined structures of CaSR in complex with G proteins from three different subfamilies: Gq, Gi and Gs. We found that the homodimeric CaSR of each complex couples to a single G protein through a common mode. This involves the C-terminal helix of each Gα subunit binding to a shallow pocket that is formed in one CaSR subunit by all three intracellular loops (ICL1-ICL3), an extended transmembrane helix 3 and an ordered C-terminal region. G-protein binding expands the transmembrane dimer interface, which is further stabilized by phospholipid. The restraint imposed by the receptor dimer, in combination with ICL2, enables G-protein activation by facilitating conformational transition of Gα. We identified a single Gα residue that determines Gq and Gs versus Gi selectivity. The length and flexibility of ICL2 allows CaSR to bind all three Gα subtypes, thereby conferring capacity for promiscuous G-protein coupling.

Immune checkpoint inhibitors or anti-claudin 18.2 antibodies? A network meta-analysis for the optimized first-line therapy of HER2-negative gastric cancer.

Background: Multiple anti-programmed cell death-1/programmed cell death-ligand 1 (PD-1/PD-L1) inhibitors and zolbetuximab, an anti-claudin 18.2 antibody, have shown efficacy in the first-line treatment of HER2-negative gastric cancers. How to choose the best regimen remains an unsolved question. Objectives: We aimed to conduct a comparative analysis of the therapeutic advantages between immunotherapy and anti-claudin-18.2-targeted therapies in the first-line treatment of HER2-negative, unresectable, or metastatic gastric cancers. Design: Network meta-analysis was employed to systematically compare efficacy and safety data derived from various clinical trials. Data sources and methods: We included phase III randomized controlled trials in PubMed, Embase, Web of Science, Cochrane Library, and major conference abstracts. Network meta-analysis was used to compare the efficacy of each first-line therapeutic agent and to indirectly compare immunotherapy with anti-claudin-18.2-targeted therapy. Results: Eight trials comprising a total of 6455 patients were included. For the overall survival (OS) analysis, no statistically significant differences were observed between pembrolizumab [hazard ratios (HR) = 1.00, 95% CI: 0.94-1.07], sintilimab (HR = 0.99, 95% CI: 0.89-1.09), sugemalimab (HR = 0.98, 95% CI: 0.87-1.10), tislelizumab (HR = 0.97, 95% CI: 0.87-1.09), zolbetuximab (HR = 0.98, 95% CI: 0.91-1.07), and nivolumab (HR = 1.00). For the progression-free survival (PFS) analysis, no statistically significant differences were observed between pembrolizumab (HR = 1.00, 95% CI: 0.93-1.06), sintilimab (HR = 0.91, 95% CI: 0.83-1.00), sugemalimab (HR = 0.92, 95% CI: 0.84-1.02), tislelizumab (HR = 0.93, 95% CI: 0.84-1.03), zolbetuximab (HR = 0.96, 95% CI: 0.88-1.05), and nivolumab (HR = 1.00). For the overall response rate analysis, all regimens presented similar effects on ORR. In addition, anti-claudin-18.2-targeted therapies presented similar OS (HR = 0.99, 95% CI: 0.95-1.04) and PFS (HR = 1.01, 95% CI: 0.91-1.12) compared to immunotherapy, although their toxicity profiles were distinct. Conclusions: Our network meta-analysis showed no significant difference in PFS, OS, or ORR between different checkpoint inhibitors or between immunotherapy and anti-claudin-18.2-targeted therapies in the first-line treatment of HER2-negative, unresectable, or metastatic gastric cancers.

Time resolution in cryo-EM using a PDMS-based microfluidic chip assembly and its application to the study of HflX-mediated ribosome recycling.

The rapid kinetics of biological processes and associated short-lived conformational changes pose a significant challenge in attempts to structurally visualize biomolecules during a reaction in real time. Conventionally, on-pathway intermediates have been trapped using chemical modifications or reduced temperature, giving limited insights. Here, we introduce a time-resolved cryo-EM method using a reusable PDMS-based microfluidic chip assembly with high reactant mixing efficiency. Coating of PDMS walls with SiO2 virtually eliminates non-specific sample adsorption and ensures maintenance of the stoichiometry of the reaction, rendering it highly reproducible. In an operating range from 10 to 1,000 ms, the device allows us to follow in vitro reactions of biological molecules at resolution levels in the range of 3 Å. By employing this method, we show the mechanism of progressive HflX-mediated splitting of the 70S E. coli ribosome in the presence of the GTP via capture of three high-resolution reaction intermediates within 140 ms.

Cryo-TEM Reveals the Influence of Multivalent Charge and PEGylation on Shape Transitions in Fluid Lipid Assemblies: From Vesicles to Discs, Rods, and Spheres.

Lipids, and cationic lipids in particular are of interest as delivery vectors for hydrophobic drugs such as the cancer therapeutic paclitaxel, and the structures of lipid assemblies affect their efficacy. We investigated the effect of incorporating the multivalent cationic lipid MVL5 (+5e) and poly(ethylene glycol)-lipids (PEG-lipids), alone and in combination, on the structure of fluid-phase lipid assemblies of the charge-neutral lipid 1,2-dioleoyl-sn-glycero-phosphocholine (DOPC). This allowed us to elucidate lipid-assembly structure correlations in sonicated formulations with high charge density, which are not accessible with univalent lipids such as the well-studied DOTAP (+1e). Cryogenic transmission electron microscopy (cryo-TEM) allowed us to determine the structure of the lipid assemblies, revealing diverse combinations of vesicles and disc-shaped, worm-like, and spherical micelles. Remarkably, MVL5 forms an essentially pure phase of disc micelles at 50 mol % MVL5. At a higher (75 mol %) content of MVL5, short- and intermediate-length worm-like micellar rods were observed, and in ternary mixtures with PEG-lipid, longer and highly flexible worm-like micelles formed. Independent of their length, the worm-like micelles coexisted with spherical micelles. In stark contrast, DOTAP forms mixtures of vesicles, disc micelles, and spherical micelles at all studied compositions, even when combined with PEG-lipids. The observed similarities and differences in the effects of charge (multivalent versus univalent) and high curvature (multivalent charge versus PEG-lipid) on the assembly structure provide insights into parameters that control the size of fluid lipid nanodiscs, relevant for future applications.

Pulmonary lymphangitis carcinomatosis: A peculiar presentation clustering in MET-amplified gastric cancer.

BACKGROUND: The clinicopathological features of MET-amplified gastric cancer (GC) and real-world data on the efficacy of MET-targeted therapies remain unknown. Pulmonary lymphangitis carcinomatosis (PLC) is a peculiar manifestation of GC, whose management has not been thoroughly described. METHODS: This study analyzed patients diagnosed with MET-amplified GC or GC with PLC at any time point of the disease course from 2011 to 2021 in two centers. Clinicopathological features and survival outcomes of MET-amplified GC were analyzed. The clinical and molecular implications of GC with PLC were discussed. RESULTS: Fifty-eight patients with MET-amplified GC and 20 patients with GC accompanied by PLC were finally enrolled for analysis (including 13 overlapped patients). GC with PLC was more common in female patients (p = 0.010), diagnosed at a younger age (p = 0.002), presented with a higher baseline ECOG PS (p = 0.016), and was more likely to develop lung metastasis (p < 0.001), and serous effusion (p = 0.026) than GC without PLC. Patients with primary MET-amplified GC had a worse prognosis than those with secondary MET-amplified GC (p = 0.005). The application of anti-MET therapy was associated with numerically prolonged survival, but the association was not statistically significant (p = 0.07). MET amplification was concentrated in patients with PLC, in which anti-MET therapies elicited a high response rate. CONCLUSIONS: MET-targeted therapies are efficacious in real-world populations with MET-amplified GC. Patients with PLC have distinct clinical and molecular features and might benefit from MET-targeted therapies.

Recurrent Cystitis Associated With 2 Programmed Death 1 Inhibitors: A Rare Case Report and Literature Review.

Immune checkpoint inhibitors (ICIs) have revolutionized the treatment of advanced cancer, however, often with immune-related adverse events (irAEs). Adverse events involving the bladder were extremely rare with only few cases. Herein, we described a rare, recurrent cystitis associated with 2 programmed death 1 inhibitors (pembrolizumab and toripalimab) in 1 patient with advanced liver cancer. Cystitis associated with toripalimab, a novel humanized programmed death 1 monoclonal antibody, was first presented in our case. Cystitis is an extremely rare irAE associated with ICIs, especially anti-programmed death 1 antibodies. With widening indications of ICIs in clinical practice, physicians should be also aware of this rare irAE.

Next stage of collaboration in East Asia gastric cancer treatment.

East Asia is a high-risk area for gastric cancer (GC). Despite the rapid progress of immunotherapy and target therapy in recent years, the median overall survival (OS) of metastatic GC is still no more than 2 years. Researchers from East Asia are active in GC clinical and molecular investigations. The collaboration of East Asia plays a vital role to further GC development. Cooperation across East Asia used to be led by Japan and South Korea. However, with the tremendous success of Chinese native drug research and development (R&D) in recent years, the new era calls for a next stage for future collaboration. With the abundance of patient resources and supportive policies from the government, China GC researches made breakthroughs in anti-human epidermal growth factor receptor 2 (HER2) drugs development and immunotherapy etc. Native programmed death 1 (PD-1) inhibitors demonstrated favorable outcomes in first-line GC treatment, early phase clinical trials also showed promising results in novel drug development in the scope of biomarker-guided precisive medicine. However, chances and challenges are both upfront to this special region. There is a lack of standardization in diagnostic and treatment protocols across Asian countries, which adds the difficulties in regional clinical trials. Poor developing countries in southeast Asia are unable to support high quality early phase clinical trials and translational studies, resource deficiency may be another challenge.

Antiviral Effect of Ginsenosides rk1 against Influenza a Virus Infection by Targeting the Hemagglutinin 1-Mediated Virus Attachment.

Influenza A virus (IAV) infections have been a serious hazard to public health everywhere. With the growing concern of drug-resistant IAV strains, there is an urgent need for novel anti-IAV medications, especially those with alternative mechanisms of action. Hemagglutinin (HA), an IAV glycoprotein, plays critical roles in the early stage of virus infection, including receptor binding and membrane fusion, making it a good target for developing anti-IAV drugs. Panax ginseng is a widely used herb in traditional medicine with extensive biological effects in various disease models, and its extract was reported to show protection in IAV-infected mice. However, the main effective anti-IAV constituents in panax ginseng remain unclear. Here, we report that ginsenoside rk1 (G-rk1) and G-rg5, out of the 23 screened ginsenosides, exhibit significant antiviral effects against 3 different IAV subtypes (H1N1, H5N1, and H3N2) in vitro. Mechanistically, G-rk1 blocked IAV binding to sialic acid in a hemagglutination inhibition (HAI) assay and an indirect ELISA assay; more importantly, we showed that G-rk1 interacted with HA1 in a dose-dependent manner in a surface plasmon resonance (SPR) analysis. Furthermore, G-rk1 treatment by intranasal inoculation effectively reduced the weight loss and mortality of mice challenged with a lethal dose of influenza virus A/Puerto Rico/8/34 (PR8). In conclusion, our findings reveal for the first time that G-rk1 possesses potent anti-IAV effects in vitro and in vivo. We have also identified and characterized with a direct binding assay a novel ginseng-derived IAV HA1 inhibitor for the first time, which could present potential approaches to prevent and treat IAV infections.

Time to surgery does not affect oncologic outcomes in locally advanced gastric cancer after neoadjuvant chemotherapy: a meta-analysis.

Aim: The authors conducted a meta-analysis to determine the association between time-to-surgery (TTS) after neoadjuvant chemotherapy and patient outcomes in locally advanced gastric cancer. Methods: Electronic databases were searched to identify potential studies, in which the authors compared patient outcomes between those with TTS within 4 (and 6) weeks of completion of neoadjuvant chemotherapy and those after 4 (and 6) weeks. Results: Six studies, including 1238 patients, were eligible for inclusion. Pooled data showed no significant differences in rates of pathological complete response, major pathological response, ypN0, complications, R0 resection and operative time between groups of longer TTS and shorter TTS. Conclusion: There was no statistically advantageous impact of prolonged TTS on pathological and surgical outcomes. Large, population-based studies are warranted.

Time resolution in cryo-EM using a novel PDMS-based microfluidic chip assembly and its application to the study of HflX-mediated ribosome recycling.

The rapid kinetics of biological processes and associated short-lived conformational changes pose a significant challenge in attempts to structurally visualize biomolecules during a reaction in real time. Conventionally, on-pathway intermediates have been trapped using chemical modifications or reduced temperature, giving limited insights. Here we introduce a novel time-resolved cryo-EM method using a reusable PDMS-based microfluidic chip assembly with high reactant mixing efficiency. Coating of PDMS walls with SiO2 virtually eliminates non-specific sample adsorption and ensures maintenance of the stoichiometry of the reaction, rendering it highly reproducible. In an operating range from 10 to 1000 ms, the device allows us to follow in vitro reactions of biological molecules at resolution levels in the range of 3 Å. By employing this method, we show for the first time the mechanism of progressive HlfX-mediated splitting of the 70S E. coli ribosome in the presence of the GTP, via capture of three high-resolution reaction intermediates within 140 ms.

Screening and identification of 3-aryl-quinolin-2-one derivatives as antiviral agents against influenza A.

Quinolin-2-one represents an important and valuable chemical motif that possesses a wide variety of biological activities; however, the anti-influenza activities of quinolin-2-one-containing compounds were rarely reported. Herein, we describe the screening and identification of 3-aryl-quinolin-2-one derivatives as a novel class of antiviral agents. The 3-aryl-quinolinone derivatives were synthesized via an efficient copper-catalyzed reaction cascade that we previously developed. Using this synthetic method, preliminary structure-activity relationships of this scaffold against the influenza A virus infection were systematically explored. The most potent compound 34 displayed IC50 values of 2.14 and 4.88 µM against the replication of H3N2 (A/HK/8/68) and H1N1 (A/WSN/33) strains, respectively, without apparent cytotoxicity on MDCK cells. We further demonstrated that 27 and 34 potently inhibited the plaque formation of the IAV, rendering this scaffold attractive for pursuing novel anti-influenza agents.

Extracellular Vesicle-Derived Protein File from Peripheral Blood Predicts Immune-Related Adverse Events in Gastric Cancer Patients Receiving Immunotherapy.

Immune checkpoint inhibitors (ICIs) initiate a new stage for gastric cancer (GC) therapeutics, and plenty of patients have already benefited from ICIs. Liquid biopsy promotes the development of precision medicine of GC. However, due to the lack of precision biomarkers of immune-related adverse events (irAEs), the safety of ICIs-treated GC patients cannot be guaranteed. In our study, GC patients treated with ICIs were included for investigating the correlation between irAEs of ICIs and corresponding outcomes. We also explored the potential of biomarkers of irAEs via EV-derived proteins. Dynamic plasma was taken from 102 ICIs-treated GC patients generated retrospectively or prospectively, who were divided into discovery and validating cohorts. Plasma EV-derived protein profiles were described, and two EV-proteins, inducible T-cell co-stimulator (EV-ICOS) and indoleamine 2,3-dioxygenase 1(EV-IDO1), from 42 vital proteins were screened to predict the prognosis of ICIs with irAEs. Our work is the first to propose that EV-proteins can predict ICIs-corresponding irAEs, which can be conducive to the diagnosis and treatment of GC patients, and to facilitate the screening of beneficiaries.

Peripheral Blood Biomarkers Predictive of Efficacy Outcome and Immune-Related Adverse Events in Advanced Gastrointestinal Cancers Treated with Checkpoint Inhibitors.

BACKGROUND: Gastrointestinal cancers constitute a major burden of global cancer mortalities. In recent years, the advent of immune checkpoint inhibitors has greatly improved the survival of patients with advanced gastrointestinal cancers, while predictive biomarkers of treatment efficacy and toxicities are still unmet demands. METHODS: In our retrospective study, patients with advanced gastrointestinal cancers who received single or double immune checkpoint inhibitors in the Department of Gastrointestinal Oncology in Peking University Cancer Hospital between July 2016 and February 2022 were enrolled. Records of clinicopathological information, survival parameters, safety data, and baseline and posttreatment peripheral blood constituents were retrieved. Cox regression analysis and logistic regression analysis were performed to identify the predictive factors of treatment outcomes and immune-related adverse events. RESULTS: We demonstrated that early treatment lines, the presence of immune-related adverse events, and a lower C2 neutrophil-to-lymphocyte ratio were independent factors predicting a superior objective response rate and progression-free survival in patients treated with immunotherapy. Lower ECOG PS, higher baseline albumin, and lower C2 neutrophil-to-lymphocyte ratios were independent risk factors for the onset of immune-related adverse events. Patients who succumbed to immune-related adverse events during immunotherapy presented better survival. CONCLUSION: Our results indicate that peripheral blood markers have potential for predicting treatment outcomes and immune-related adverse events in patients with advanced gastrointestinal cancer. Prospective validations are warranted.

Intermediates in SARS-CoV-2 spike-mediated cell entry.

SARS-CoV-2 cell entry is completed after viral spike (S) protein-mediated membrane fusion between viral and host cell membranes. Stable prefusion and postfusion S structures have been resolved by cryo-electron microscopy and cryo-electron tomography, but the refolding intermediates on the fusion pathway are transient and have not been examined. We used an antiviral lipopeptide entry inhibitor to arrest S protein refolding and thereby capture intermediates as S proteins interact with hACE2 and fusion-activating proteases on cell-derived target membranes. Cryo-electron tomography imaged both extended and partially folded intermediate states of S2, as well as a novel late-stage conformation on the pathway to membrane fusion. The intermediates now identified in this dynamic S protein-directed fusion provide mechanistic insights that may guide the design of CoV entry inhibitors.

Does first-line immunotherapy impact the efficacy of later treatments: a discussion on the use of second progression-free survival as a research endpoint.

Currently, cancer immunotherapy efficacy is measured by endpoints, such as progression-free survival and overall survival, that are unable to reflect authentic responses to checkpoint inhibitors in clinical trials. Second progression-free survival, however, could be an ideal surrogate endpoint due to its easy measurability, correlation with overall survival, and ability to evaluate the efficacy of sequential therapies. This commentary summarizes second progression-free survival data from clinical trials investigating first-line anti-PD-1/PD-L1 therapy in patients with metastatic solid tumors. We speculate that first-line immunotherapies exert a positive influence on the efficacy of later therapies in patients with a few cancer types, though additional research is urgently warranted.

Fe/Co redox and surficial hydroxyl potentiation in the FeCo2O4 enhanced Co3O4/persulfate process for TC degradation.

A magnetic FeCo2O4/Co3O4 nanocomposite was successfully synthesized by a facile hydrothermal method as an efficient activator for persulfate (PS) activation to degrade tetracycline (TC) in an aqueous solution. TC removal and mineralization efficiencies reached up to 91.63% and 43.57% in 120 min in the FCC-3/PS system, respectively. The mixed-valence of Fe/Co in the nanocomposite catalyst was beneficial for electrons transfer between Co and Fe elements and enhanced the redox circulation of Fe and Co in between divalent and trivalent. Surficial analysis and phosphate adsorption test confirmed the existence of -OH groups on the surfaces of FeCo2O4/Co3O4 nanocomposite. Fe/Co redox and surficial hydroxyl in the catalyst played significant roles in the TC potentiation degradation, which was contributed by the plenty of adsorbed -OH groups and excellent dispersity of FeCo2O4 in the FeCo2O4/Co3O4 composite. The sulfate radicals were major species followed by the hydroxyl radicals, and the surficial adsorbed hydroxyl made great contributions to radical generation. The cycling test and intermediate toxicity analysis indicated that the nanocomposite was considered stable and practicable in water treatment. This work demonstrated that the FeCo2O4/Co3O4 nanocomposite was an effective and environ-friendly catalyst towards PS activation for removing organic pollutants from water.

Comparison of Treatment Efficacy and Survival Outcomes Between Asian and Western Patients With Unresectable Gastric or Gastro-Esophageal Adenocarcinoma: A Systematic Review and Meta-Analysis.

Background: Gastric cancer and gastro-esophageal adenocarcinoma are geographically heterogeneous diseases. Previous studies suggested that Asian and Western patients with late-stage gastric or gastro-esophageal adenocarcinoma possess distinct survival outcomes. However, the interregional differences of multiple systemic therapies in unresectable diseases have not been comprehensively described. Materials and Methods: We searched PubMed-MEDLINE, Embase, Web of Science and Cochrane Library from inception to 31 October 2021 and reviewed major conference abstracts for controlled trials of systemic therapies in unresectable gastric or gastro-esophageal adenocarcinoma that reported hazard ratios stratified by geographical region. The primary measurements were overall survival and progression-free survival. The pooled hazard ratios and 95% confidence intervals for overall survival and progression-free survival in Asian and Western populations were calculated using a random effect model. A linear regression model was adopted to compare the overall survival and progression-free survival between Asian and Western patients. Results: A total of 9033 patients from 20 studies were included for analysis. Immunotherapy was associated with an improvement in the overall survival for both Asian (hazard ratio, 0.80; 95% confidence interval, 0.65-0.98) and Western (hazard ratio, 0.90; 95% confidence interval, 0.81-1.00) patients, with no significant difference between the two groups (P = 0.32). Trends of survival benefit with anti-HER2 therapy and anti-angiogenic therapy versus control were observed in both Asian and Western patients, although statistical significance was not denoted. Subgroup analyses yielded a statistically superior overall survival of Asian versus Western patients in trials that investigated first-line immunotherapy (P = 0.04). Due to the linear regression analyses with scatter plot graphs, Asian patients showed a higher overall survival, but not progression-free survival, than Western patients irrespective of treatment type. Conclusion: Asian and Western patients with unresectable gastric or gastro-esophageal adenocarcinoma show similar responses to systemic therapies with limited interregional differences. Exceptionally, first-line immunotherapy could elicit superior survival among Asian populations. In addition, Asian patients with gastric or gastro-esophageal adenocarcinoma display a superior OS compared with Western counterparts.

Cryo-EM structure of the SARS-CoV-2 Omicron spike.

The recently reported B.1.1.529 Omicron variant of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) includes 34 mutations in the spike protein relative to the Wuhan strain, including 15 mutations in the receptor-binding domain (RBD). Functional studies have shown Omicron to substantially escape the activity of many SARS-CoV-2-neutralizing antibodies. Here, we report a 3.1 Å-resolution cryoelectron microscopy (cryo-EM) structure of the Omicron spike protein ectodomain. The structure depicts a spike that is exclusively in the 1-RBD-up conformation with high mobility of RBD. Many mutations cause steric clashes and/or altered interactions at antibody-binding surfaces, whereas others mediate changes of the spike structure in local regions to interfere with antibody recognition. Overall, the structure of the Omicron spike reveals how mutations alter its conformation and explains its extraordinary ability to evade neutralizing antibodies.