Directed Assembly of Homopentameric Cholera Toxin B‑Subunit Proteins into Higher-Order Structures Using Coiled-Coil Appendages

The self-assembly of proteins into higher order structures is ubiquitous in living systems. It is also an essential process for the bottom-up creation of novel molecular architectures and devices for synthetic biology. However, the complexity of protein-protein interaction surfaces makes it challenging to mimic natural assembly processes in artificial systems. Indeed, many successful computationally designed protein assemblies are pre-screened for ‘designability’, limiting the choice of components. Here, we report a simple and pragmatic strategy to assemble chosen multi-subunit proteins into more complex structures. A coiled-coil domain appended to one face of the pentameric cholera toxin B-subunit (CTB) enabled the ordered assembly of tubular supra-molecular complexes. X-ray crystallography and analysis of a tubular structure has revealed a hierarchical assembly process that displays features reminiscent of the polymorphic assembly of polyomavirus proteins. The approach provides a simple and straightforward method to direct the assembly of protein building blocks which present either termini on a single face of an oligomer. This scaffolding approach can be used to generate bespoke supramolecular assemblies of functional proteins. Additionally, structural resolution of the scaffolded assemblies highlight ‘native-state’ forced protein-protein interfaces, which may prove useful as starting conformations for future computational design

Safety and Efficacy of Durvalumab With or Without Tremelimumab in Patients With PD-L1-Low/Negative Recurrent or Metastatic HNSCC The Phase 2 CONDOR Randomized Clinical Trial

IMPORTANCE: Dual blockade of programmed death ligand 1(PD-L1) and cytotoxic T-lymphocyte associated protein 4 (CTLA-4) may overcome immune checkpoint inhibition. It is unknown whether dual blockade can potentiate antitumor activity without compromising safety in patients with recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC) and low or no PD-L1 tumor cell expression. OBJECTIVE :To assess safety and objective response rate of durvalumab combined with tremelimumab. DESIGN, SETTING, AND PARTICIPANTS: The CONDOR study was a phase 2, randomized, open-label study of Durvalumab, Tremelimumab, and Durvalumab in Combination With Tremelimumab in Patients With R/M HNSCC. Eligibility criteria included PD-L1-low/negative disease that had progressed after 1 platinum-containing regimen in the R/M setting. Patients were randomized (N = 267) from April 15, 2015, to March 16, 2016, at 127 sites in North America, Europe, and Asia Pacific. INTERVENTIONS: Durvalumab (20 mg/kg every 4 weeks) + tremelimumab (1 mg/kg every 4 weeks) for 4 cycles, followed by durvalumab (10 mg/kg every 2 weeks), or durvalumab (10 mg/kg every 2 weeks) monotherapy, or tremelimumab (10 mg/kg every 4 weeks for 7 doses then every 12 weeks for 2 doses) monotherapy. MAIN OUTCOMES AND MEASURES: Safety and tolerability and efficacy measured by objective response rate. RESULTS: Among the 267 patients (220 men [82.4%]), median age (range) of patients was 61.0 (23-82) years. Grade 3/4 treatment-related adverse events occurred in 21 patients (15.8%) treated with durvalumab + tremelimumab, 8 (12.3%) treated with durvalumab, and 11 (16.9%) treated with tremelimumab. Grade 3/4 immune-mediated adverse events occurred in 8 patients (6.0%) in the combination arm only. Objective response rate (95% CI) was 7.8% (3.78%1339%) in the combination arm (n =129), 9.2% (3.46%-19.02%) for durvalumab monotherapy (n = 65), and 1.6% (0.04%-8.53%) for tremelimumab monotherapy (n = 63); median overall survival (95% CI) for all patients treated was 7.6 (4.9-10.6), 6.0 (4.0-11.3), and 5.5 (3.9-7.0) months, respectively. CONCLUSIONS AND RELEVANCE: In patients with R/M HNSCC and low or no PD-Lt tumor cell expression, all 3 regimens exhibited a manageable toxicity profile. Durvalumab and durvalumab + tremelimumab resulted in clinical benefit, with minimal observed difference between the two. A phase 3 study is under way

Membrane Fusion Mediated by Non-covalent Binding of Re-engineered Cholera Toxin Assemblies to Glycolipids

Membrane fusion is essential for the transport of macromolecules and viruses across membranes. While glycan-binding proteins (lectins) often initiate cellular adhesion, subsequent fusion events require additional protein machinery. No mechanism for membrane fusion arising from simply a protein binding to membrane glycolipids has been described thus far. Herein, we report that a biotinylated protein derived from cholera toxin becomes a fusogenic lectin upon cross-linking with streptavidin. This novel reengineered protein brings about hemifusion and fusion of vesicles as demonstrated by mixing of fluorescently labeled lipids between vesicles as well as content mixing of liposomes filled with fluorescently labeled dextran. Exclusion of the complex at vesicle–vesicle interfaces could also be observed, indicating the formation of hemifusion diaphragms. Discovery of this fusogenic lectin complex demonstrates that new emergent properties can arise from simple changes in protein architecture and provides insights into new mechanisms of lipid-driven fusion

Lesson from the Stoichiometry Determination of the Cohesin Complex: A Short Protease Mediated Elution Increases the Recovery from Cross-Linked Antibody-Conjugated Beads

Affinity purification of proteins using antibodies coupled to beads and subsequent mass spectrometric analysis has become a standard technique for the identification of protein complexes. With the recent transfer of the isotope dilution mass spectrometry principle (IDMS) to the field of proteomics, quantitative analysesssuch as the stoichiometry determination of protein complexesshave become achievable. Traditionally proteins were eluted from antibody-conjugated beads using glycine at low pH or using diluted acids such as HCl, TFA, or FA, but elution was often found to be incomplete. Using the cohesin complex and the anaphase promoting complex/cyclosome (APC/C) as examples, we show that a short 15-60 min predigestion with a protease such as LysC (modified on-bead digest termed protease elution) increases the elution efficiency 2- to 3-fold compared to standard acid elution protocols. While longer incubation periodssas performed in standard on-bead digestionsled to partial proteolysis of the cross-linked antibodies, no or only insignificant cleavage was observed after 15-60 min protease mediated elution. Using the protease elution method, we successfully determined the stoichiometry of the cohesin complex by absolute quantification of the four core subunits using LC-SRM analysis and 19 reference peptides generated with the EtEP strategy. Protease elution was 3-fold more efficient compared to HCl elution, but measurements using both elution techniques are in agreement with

In Vivo Human Apolipoprotein E Isoform Fractional Turnover Rates in the CNS

Apolipoprotein E (ApoE) is the strongest genetic risk factor for Alzheimer’s disease and has been implicated in the risk for other neurological disorders. The three common ApoE isoforms (ApoE2, E3, and E4) each differ by a single amino acid, with ApoE4 increasing and ApoE2 decreasing the risk of Alzheimer’s disease (AD). Both the isoform and amount of ApoE in the brain modulate AD pathology by altering the extent of amyloid beta (Aβ) peptide deposition. Therefore, quantifying ApoE isoform production and clearance rates may advance our understanding of the role of ApoE in health and disease. To measure the kinetics of ApoE in the central nervous system (CNS), we applied in vivo stable isotope labeling to quantify the fractional turnover rates of ApoE isoforms in 18 cognitively-normal adults and in ApoE3 and ApoE4 targeted-replacement mice. No isoform-specific differences in CNS ApoE3 and ApoE4 turnover rates were observed when measured in human CSF or mouse brain. However, CNS and peripheral ApoE isoform turnover rates differed substantially, which is consistent with previous reports and suggests that the pathways responsible for ApoE metabolism are different in the CNS and the periphery. We also demonstrate a slower turnover rate for CSF ApoE than that for amyloid beta, another molecule critically important in AD pathogenesis

Sortase-Modified Cholera Toxoids Show Specific Golgi Localization

Cholera toxoid is an established tool for use in cellular tracing in neuroscience and cell biology. We use a sortase labeling approach to generate site-specific N-terminally modified variants of both the A2-B5 heterohexamer and B5 pentamer forms of the toxoid. Both forms of the toxoid are endocytosed by GM1-positive mammalian cells, and while the heterohexameric toxoid was principally localized in the ER, the B5 pentamer showed an unexpectedly specific localization in the medial/trans-Golgi. This study suggests a future role for specifically labeled cholera toxoids in live-cell imaging beyond their current applications in neuronal tracing and labeling of lipid rafts in fixed cells

Dimethyl fumarate in patients admitted to hospital with COVID-19 (RECOVERY): a randomised, controlled, open-label, platform trial

Dimethyl fumarate (DMF) inhibits inflammasome-mediated inflammation and has been proposed as a treatment for patients hospitalised with COVID-19. This randomised, controlled, open-label platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]), is assessing multiple treatments in patients hospitalised for COVID-19 (NCT04381936, ISRCTN50189673). In this assessment of DMF performed at 27 UK hospitals, adults were randomly allocated (1:1) to either usual standard of care alone or usual standard of care plus DMF. The primary outcome was clinical status on day 5 measured on a seven-point ordinal scale. Secondary outcomes were time to sustained improvement in clinical status, time to discharge, day 5 peripheral blood oxygenation, day 5 C-reactive protein, and improvement in day 10 clinical status. Between 2 March 2021 and 18 November 2021, 713 patients were enroled in the DMF evaluation, of whom 356 were randomly allocated to receive usual care plus DMF, and 357 to usual care alone. 95% of patients received corticosteroids as part of routine care. There was no evidence of a beneficial effect of DMF on clinical status at day 5 (common odds ratio of unfavourable outcome 1.12; 95% CI 0.86-1.47; p = 0.40). There was no significant effect of DMF on any secondary outcome

Convalescent plasma in patients admitted to hospital with COVID-19 (RECOVERY): a randomised controlled, open-label, platform trial

Background: Many patients with COVID-19 have been treated with plasma containing anti-SARS-CoV-2 antibodies. We aimed to evaluate the safety and efficacy of convalescent plasma therapy in patients admitted to hospital with COVID-19. Methods: This randomised, controlled, open-label, platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]) is assessing several possible treatments in patients hospitalised with COVID-19 in the UK. The trial is underway at 177 NHS hospitals from across the UK. Eligible and consenting patients were randomly assigned (1:1) to receive either usual care alone (usual care group) or usual care plus high-titre convalescent plasma (convalescent plasma group). The primary outcome was 28-day mortality, analysed on an intention-to-treat basis. The trial is registered with ISRCTN, 50189673, and ClinicalTrials.gov, NCT04381936. Findings: Between May 28, 2020, and Jan 15, 2021, 11558 (71%) of 16287 patients enrolled in RECOVERY were eligible to receive convalescent plasma and were assigned to either the convalescent plasma group or the usual care group. There was no significant difference in 28-day mortality between the two groups: 1399 (24%) of 5795 patients in the convalescent plasma group and 1408 (24%) of 5763 patients in the usual care group died within 28 days (rate ratio 1·00, 95% CI 0·93–1·07; p=0·95). The 28-day mortality rate ratio was similar in all prespecified subgroups of patients, including in those patients without detectable SARS-CoV-2 antibodies at randomisation. Allocation to convalescent plasma had no significant effect on the proportion of patients discharged from hospital within 28 days (3832 [66%] patients in the convalescent plasma group vs 3822 [66%] patients in the usual care group; rate ratio 0·99, 95% CI 0·94–1·03; p=0·57). Among those not on invasive mechanical ventilation at randomisation, there was no significant difference in the proportion of patients meeting the composite endpoint of progression to invasive mechanical ventilation or death (1568 [29%] of 5493 patients in the convalescent plasma group vs 1568 [29%] of 5448 patients in the usual care group; rate ratio 0·99, 95% CI 0·93–1·05; p=0·79). Interpretation: In patients hospitalised with COVID-19, high-titre convalescent plasma did not improve survival or other prespecified clinical outcomes. Funding: UK Research and Innovation (Medical Research Council) and National Institute of Health Research