Tertiary folds of the SL5 RNA from the 5' proximal region of SARS-CoV-2 and related coronaviruses.

Coronavirus genomes sequester their start codons within stem-loop 5 (SL5), a structured, 5' genomic RNA element. In most alpha- and betacoronaviruses, the secondary structure of SL5 is predicted to contain a four-way junction of helical stems, some of which are capped with UUYYGU hexaloops. Here, using cryogenic electron microscopy (cryo-EM) and computational modeling with biochemically determined secondary structures, we present three-dimensional structures of SL5 from six coronaviruses. The SL5 domain of betacoronavirus severe-acute-respiratory-syndrome-related coronavirus 2 (SARS-CoV-2), resolved at 4.7 Å resolution, exhibits a T-shaped structure, with its UUYYGU hexaloops at opposing ends of a coaxial stack, the T's "arms." Further analysis of SL5 domains from SARS-CoV-1 and MERS (7.1 and 6.4 to 6.9 Å resolution, respectively) indicate that the junction geometry and inter-hexaloop distances are conserved features across these human-infecting betacoronaviruses. The MERS SL5 domain displays an additional tertiary interaction, which is also observed in the non-human-infecting betacoronavirus BtCoV-HKU5 (5.9 to 8.0 Å resolution). SL5s from human-infecting alphacoronaviruses, HCoV-229E and HCoV-NL63 (6.5 and 8.4 to 9.0 Å resolution, respectively), exhibit the same coaxial stacks, including the UUYYGU-capped arms, but with a phylogenetically distinct crossing angle, an X-shape. As such, all SL5 domains studied herein fold into stable tertiary structures with cross-genus similarities and notable differences, with implications for potential protein-binding modes and therapeutic targets.

Efficacy study of platelet-rich plasma combined with core decompression and bone grafting in the treatment of early-stage avascular necrosis of the femoral head: a retrospective study.

OBJECTIVE: This study aimed to evaluate the effectiveness of combined core decompression (CD), bone grafting (BG), and platelet-rich plasma (PRP) in treating early-stage avascular necrosis of the femoral head (ANFH). METHODS: A retrospective study was conducted on 74 patients (85 hips) with Ficat-Arlet stage I-II ANFH who were treated at our hospital between May 2015 and May 2018. The control group (20 patients, 22 hips) received symptomatic treatments, including weight-bearing reduction and oral analgesics. The CD + BG group (29 patients, 34 hips) underwent CD and ß-tricalcium phosphate bone grafting. The PRP combination group (25 patients, 29 hips) received PRP injections in addition to CD and BG. Patients were followed up for five years to assess the necessity for total hip arthroplasty (THA). Data analysis was performed on those from the CD + BG and PRP groups who did not require THA. Clinical outcomes were evaluated using the Visual Analog Scale (VAS), Harris Hip Score (HHS), and the proportion of patients not accepting THA. RESULTS: At the five-year follow-up, the rate of THA in the control group was 68.18% (15/22), while in the CD + BG group and the PRP combination group, the rates were 17.65% (6/34) and 10.34% (3/29), respectively. There was no statistically significant difference between the CD + BG group and the PRP combination group (P = 0.441), but both differed significantly from the control group (P < 0.001). Kaplan-Meier survival analysis showed that over time, the proportion of patients in the PRP combination group who did not require THA was consistently higher than that in the CD + BG group. Among patients who did not undergo THA, the proportion of Ficat-Arlet stage I-II patients in the PRP combination group was 88.46% (23/26), which was higher than the 64.29% (18/28) in the CD + BG group, showing a significant difference (P = 0.038). VAS score and HHS were compared between the two groups at 6 months, 12 months, and the last follow-up point, with patients in the PRP combination group showing better scores than those in the CD + BG group (p < 0.05) in both metrics. CONCLUSION: The combination therapy of CD, BG, and PRP demonstrates significant advantages in improving symptoms and delaying disease progression in early-stage ANFH.

Molecular Evolution of SNAREs in Vitis vinifera and Expression Analysis under Phytohormones and Abiotic Stress.

SNARE proteins (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) play a key role in mediating a variety of plant biological processes. Currently, the function of the SNARE gene family in phytohormonal and abiotic stress treatments in grapevine is currently unknown, making it worthwhile to characterize and analyze the function and expression of this family in grapevine. In the present study, 52 VvSNARE genes were identified and predominantly distributed on 18 chromosomes. Secondary structures showed that the VvSNARE genes family irregular random coils and α-helices. The promoter regions of the VvSNARE genes were enriched for light-, abiotic-stress-, and hormone-responsive elements. Intraspecific collinearity analysis identified 10 pairs collinear genes within the VvSNARE family and unveiled a greater number of collinear genes between grapevine and apple, as well as Arabidopsis thaliana, but less associations with Oryza sativa. Quantitative real-time PCR (qRT-PCR) analyses showed that the VvSNARE genes have response to treatments with ABA, NaCl, PEG, and 4 °C. Notably, VvSNARE2, VvSNARE14, VvSNARE15, and VvSNARE17 showed up-regulation in response to ABA treatment. VvSNARE2, VvSNARE15, VvSNARE18, VvSNARE19, VvSNARE20, VvSNARE24, VvSNARE25, and VvSNARE29 exhibited significant up-regulation when exposed to NaCl treatment. The PEG treatment led to significant down-regulation of VvSNARE1, VvSNARE8, VvSNARE23, VvSNARE25, VvSNARE26, VvSNARE31, and VvSNARE49 gene expression. The expression levels of VvSNARE37, VvSNARE44, and VvSNARE46 were significantly enhanced after exposure to 4 °C treatment. Furthermore, subcellular localization assays certified that VvSNARE37, VvSNARE44, and VvSNARE46 were specifically localized at the cell membrane. Overall, this study showed the critical role of the VvSNARE genes family in the abiotic stress response of grapevines, thereby providing novel candidate genes such as VvSNARE37, VvSNARE44, and VvSNARE46 for further exploration in grapevine stress tolerance research.

Multi-Enzymatic Cascade for Efficient Deracemization of dl-Pantolactone into d-Pantolactone.

d-pantolactone is an intermediate in the synthesis of d-pantothenic acid, which is known as vitamin B5. The commercial synthesis of d-pantolactone is carried out through the selective resolution of dl-pantolactone catalyzed by lactone hydrolase. In contrast to a kinetic resolution approach, the deracemization of dl-pantolactone is a simpler, greener, and more sustainable way to obtain d-pantolactone with high optical purity. Herein, an efficient three-enzyme cascade was developed for the deracemization of dl-pantolactone, using l-pantolactone dehydrogenase from Amycolatopsis methanolica (AmeLPLDH), conjugated polyketone reductase from Zygosaccharomyces parabailii (ZpaCPR), and glucose dehydrogenase from Bacillus subtilis (BsGDH). The AmeLPLDH was used to catalyze the dehydrogenated l-pantolactone into ketopantolactone; the ZpaCPR was used to further catalyze the ketopantolactone into d-pantolactone; and glucose dehydrogenase together with glucose fulfilled the function of coenzyme regeneration. All three enzymes were co-expressed in E. coli strain BL21(DE3), which served as the whole-cell biocatalyst. Under optimized conditions, 36 h deracemization of 1.25 M dl-pantolactone d-pantolactone led to an e.e.p value of 98.6%, corresponding to productivity of 107.7 g/(l·d).

Enantioselective De Novo Synthesis of α,α-Diaryl Ketones from Alkynes.

Chiral α,α-diaryl ketones are structural motifs commonly present in bioactive molecules, and they are also valuable building blocks in synthetic organic chemistry. However, catalytic asymmetric synthesis of α,α-diaryl ketones bearing a tertiary stereogenic center remains largely unsolved. Herein, we report a catalytic de novo enantioselective synthesis of α,α-diaryl ketones from simple alkynes via chiral phosphoric acid (CPA) catalysis. A broad range of enolizable α,α-diaryl ketones are prepared in good yields and with excellent enantioselectivities. The described protocol also serves as an efficient deuteration method for the preparation of enantiomerically enriched deuterated α,α-diaryl ketones. Using the methodology reported, bioactive molecules, including one of the best-selling anti-breast cancer drugs, tamoxifen, are readily synthesized.

Nickel-Hydride-Catalyzed Diastereo- and Enantioselective Hydroalkylation of Cyclopropenes.

Cyclopropanes are structural motifs that are widely present in natural products and bioactive molecules, and they are also tremendously useful building blocks in synthetic organic chemistry. Asymmetric synthesis of cyclopropane derivatives has been an intensively researched area over the years, but efficient asymmetric preparation of alkylcyclopropane scaffolds remains a challenging topic. Herein, we report a nickel-hydride-catalyzed enantioselective and diastereoselective hydroalkylation of cyclopropenes for facile synthesis of chiral alkylcyclopropane motifs. The reported method is efficient and versatile, taking place under mild reaction conditions, and having broad applicability and excellent functional group tolerance.

Catalytic Asymmetric Construction of α,α-Diaryl Aldehydes via Oxo-Hydroarylation of Terminal Alkynes.

Chiral aldehydes containing a tertiary stereogenic center are versatile building blocks in organic chemistry. In particular, such structural motifs bearing an α,α-diaryl moiety are very challenging scaffolds and their efficient asymmetric synthesis is not reported. In this work, a phosphoric acid-catalyzed enantioselective synthesis of α,α-diaryl aldehydes from simple terminal alkynes is presented. This approach yields a wide range of highly enolizable α,α-diaryl aldehydes in good yields with excellent enantioselectivities. Facile transformations of the products, as well as an efficient synthesis of bioactive molecules, including an effective anti-smallpox agent and an FDA-approved antidepressant drug (+)-sertraline, are demonstrated.

Copper-catalyzed atroposelective synthesis of C-O axially chiral compounds enabled by chiral 1,8-naphthyridine based ligands.

Axially chiral molecular scaffolds are widely present in therapeutic agents, natural products, catalysts, and advanced materials. The construction of such molecules has garnered significant attention from academia and industry. The catalytic asymmetric synthesis of axially chiral biaryls, along with other non-biaryl axially chiral molecules, has been extensively explored in the past decade. However, the atroposelective synthesis of C-O axial chirality remains largely underdeveloped. Herein, we document a copper-catalyzed atroposelective construction of C-O axially chiral compounds using novel 1,8-naphthyridine-based chiral ligands. Mechanistic investigations have provided good evidence in support of a mechanism involving synergistic interplay between a desymmetrization reaction and kinetic resolution process. The method described in this study holds great significance for the atroposelective synthesis of C-O axially chiral compounds, with promising applications in organic chemistry. The utilization of 1,8-naphthyridine-based ligands in copper catalysis is anticipated to find broad applications in asymmetric copper(i)-catalyzed azide-alkyne cycloadditions (CuAACs) and beyond.

Study on the efficacy of 3D printing technology combined with customized plates for the treatment of complex tibial plateau fractures.

BACKGROUND: Anatomical reduction and stable fixation of complex tibial plateau fractures remain challenging in clinical practice. This study examines the efficacy of using 3D printing technology combined with customized plates for treating these fractures. METHODS: We retrospectively analyzed 22 patients treated with 3D printing and customized plates at the Orthopedic Department of the Central Hospital affiliated with Shenyang Medical College from September 2020 to January 2023. These patients were matched with 22 patients treated with traditional plates with similar baseline characteristics. Patients were divided into an experimental group (3D-printed models and customized plates) and a control group (traditional plates). The control group underwent traditional surgical methods, while the experimental group had a preoperative 3D model and customized plates for surgical planning. We compared baseline characteristics and recorded various indicators, including preoperative preparation time, surgical time, intraoperative blood loss, number of intraoperative fluoroscopies, hospital stay duration, fracture healing time, complications, knee joint range of motion (ROM), Rasmussen anatomical and functional scores, and HSS scores. RESULTS: All surgeries were successful with effective follow-up. The experimental group had shorter surgical time, less intraoperative blood loss, and fewer intraoperative fluoroscopies (P < 0.05). At 6 months and 1 year postoperatively, the experimental group had better knee joint HSS scores than the control group. Preoperative preparation time and total hospital stay were shorter in the control group (P < 0.05). There were no significant differences in fracture healing time and follow-up duration between groups. The experimental group showed better knee joint flexion angles (P < 0.05). Rasmussen scores showed no statistical difference between groups (P > 0.05). The incidence of complications was slightly lower in the experimental group but not significantly different. CONCLUSION: 3D printing technology combined with customized plates for complex tibial plateau fractures enables precise articular surface reduction, significantly shortens surgical time, and reduces intraoperative blood loss. This method improves knee joint function, offering a more effective treatment option.

Treatment of complex limb fractures with 3D printing technology combined with personalized plates: a retrospective study of case series and literature review.

Background: In recent years, 3D printing technology has made significant strides in the medical field. With the advancement of orthopedics, there is an increasing pursuit of high surgical quality and optimal functional recovery. 3D printing enables the creation of precise physical models of fractures, and customized personalized steel plates can better realign and more comprehensively and securely fix fractures. These technologies improve preoperative diagnosis, simulation, and planning for complex limb fractures, providing patients with better treatment options. Patients and methods: Five typical cases were selected from a pool of numerous patients treated with 3D printing technology combined with personalized custom steel plates at our hospital. These cases were chosen to demonstrate the entire process of printing 3D models and customizing individualized steel plates, including details of the patients' surgeries and treatment procedures. Literature reviews were conducted, with a focus on highlighting the application of 3D printing technology combined with personalized custom steel plates in the treatment of complex limb fractures. Results: 3D printing technology can produce accurate physical models of fractures, and personalized custom plates can achieve better fracture realignment and more comprehensive and robust fixation. These technologies provide patients with better treatment options. Conclusion: The use of 3D printing models and personalized custom steel plates can improve preoperative diagnosis, simulation, and planning for complex limb fractures, realizing personalized medicine. This approach helps reduce surgical time, minimize trauma, enhance treatment outcomes, and improve patient functional recovery.

Disappearance of femoral head shortly after femoral neck fracture: a case report and literature review.

This case report describes a woman in her 70s who presented with a 3-month history of hip pain and inability to walk. Upon admission, she was diagnosed with the extremely rare condition of complete femoral head disappearance. A comprehensive examination was conducted to determine the cause and devise an effective treatment strategy, taking the patient's medical history into account. Through interdisciplinary discussions, occult infection and other potential causes were ruled out. The femoral head disappearance was ultimately determined to be due to wear, ischemia, and absorption following a fracture. After informing the patient of the diagnosis and treatment plan, total hip arthroplasty was proposed. This case highlights the rarity and severity of femoral head disappearance in patients with femoral neck fractures, emphasizing the effectiveness of total hip arthroplasty and appropriate joint prostheses in managing such cases. This case has significant implications for clinical diagnosis, treatment, and complication prevention. The report also discusses the causes of acquired femoral head disappearance, relevant diagnostic assessments, and alternative treatment options.

Study on the therapeutic effect of Kirschner wire tension band combined with anchor cross-stitch technique in the treatment of comminuted patellar inferopolar fractures.

PURPOSES: Fractures of the inferior patellar pole, unlike other patellar fractures, present challenges for traditional surgical fixation methods. This article introduces the clinical technique and outcomes of using Kirschner wire tension band combined with anchor screw cross-stitch fixation for comminuted inferior patellar pole fractures. METHODS: This retrospective case series study included 14 patients with comminuted inferior patellar pole fractures treated at our institution from September 1, 2020, to April 30, 2022. All patients underwent surgery using the Kirschner wire tension band with anchor screw cross-stitch technique. Follow-up assessments involved postoperative X-rays to evaluate fracture healing, as well as clinical parameters such as healing time, Visual Analog Scale (VAS) scores, range of motion (ROM), and Bostman scores. RESULTS: All patients were followed for an average of over 12 months, with no cases of internal fixation failure. Knee joint stability and function were excellent. X-rays revealed an average healing time of approximately 10.79 ± 1.53 weeks, hospitalization lasted 5.64 ± 1.15 days, surgery took approximately 37.86 ± 5.32 minutes, and intraoperative blood loss was 33.29 ± 8.15 ml. One patient experienced irritation from the internal fixation material. At the final follow-up, the Bostman score averaged 28.29 ± 0.83, knee joint flexion reached 131.07° ± 4.88°, all patients achieved full knee extension, and the VAS score was 0.36 ± 0.63. CONCLUSION: Kirschner wire tension band with anchor screw cross-stitch fixation for comminuted inferior patellar pole fractures delivered satisfactory clinical outcomes. This surgical method, characterized by its simplicity and reliability, is a valuable addition to clinical practice.

The combined application of pulsed electromagnetic fields and platelet-rich plasma in the treatment of early-stage knee osteoarthritis: A randomized clinical trial.

BACKGROUND: This study aims to evaluate the therapeutic efficacy of combined treatment with pulsed electromagnetic fields (PEMFs) and platelet-rich plasma (PRP) injection in improving pain and functional mobility among patients with early-stage knee osteoarthritis (KOA). We hypothesize that this combined therapy can yield superior treatment outcomes. METHODS: Based on the different treatment regimens, we divided 48 patients diagnosed with Kellgren-Lawrence grades I-III KOA into 3 groups: the PRP group, the PEMFs group, and the PRP + PEMFs group. Each subtype of KOA patients was randomly assigned to different treatment groups. In the PRP group, patients received intra-articular injections of leukocyte-rich platelet-rich plasma once a month for 3 consecutive months. In the PEMFs group, patients receive low-frequency PEMFs irradiation therapy with a frequency of 30 Hz and intensity of 1.5 mT, once daily, 5 times a week, for a consecutive treatment period of 12 weeks. In the PRP + PEMFs group, patients receive both of the aforementioned treatment protocol. The treatment effects on patients are evaluated at baseline and at weeks 4, 8, and 12 post-treatment. Assessment parameters include visual analog scale for pain, Western Ontario and McMaster Universities Osteoarthritis Index, Lequesne Index score, and knee joint range of motion. RESULTS: From the 4th to the 12th week of treatment, the visual analog scale scores, Western Ontario and McMaster Universities Osteoarthritis Index scores, and Lequesne index scores of patients in all 3 groups gradually decreased, while knee joint mobility gradually increased (P < .05). At weeks 4, 8, and 12 after treatment, the PRP combined with PEMFs group showed significantly better scores compared to the PRP group and the PEMFs group, with statistically significant differences (P < .05). A total of 7 patients experienced adverse reactions such as knee joint swelling, low-grade fever, and worsening knee joint pain after treatment, all of which disappeared within 1 week after treatment. The incidence of complications did not differ significantly among the 3 groups (P = .67). CONCLUSION: PRP, PEMFs, and the combination of PRP and PEMFs therapy all effectively alleviate knee joint pain and improve joint function. However, compared to single treatment modalities, the combined therapy of PRP and PEMFs demonstrates more pronounced efficacy.

DNA adductomics aided rapid screening of genotoxic impurities using nucleosides and 3D bioprinted human liver organoids.

Current genotoxicity assessment methods are mainly employed to verify the genotoxic safety of drugs, but do not allow for rapid screening of specific genotoxic impurities (GTIs). In this study, a new approach for the recognition of GTIs has been proposed. It is to expose the complex samples to an in vitro nucleoside incubation model, and then draw complete DNA adduct profiles to infer the structures of potential genotoxic impurities (PGIs). Subsequently, the genotoxicity is confirmed in human by 3D bioprinted human liver organoids. To verify the feasibility of the approach, lansoprazole chloride compound (Lanchlor), a PGI during the synthesis of lansoprazole, was selected as the model drug. After confirming genotoxicity by Comet assay, it was exposed to different models to map and compare the DNA adduct profiles by LC-MS/MS. The results showed Lanchlor could generate diverse DNA adducts, revealing firstly its genotoxicity at molecular mechanism of action. Furthermore, the largest variety and content of DNA adducts were observed in the nucleoside incubation model, while the human liver organoids exhibited similar results with rats. The results showed that the combination of DNA adductomics and 3D bioprinted organoids were useful for the rapid screening of GTIs.

Saponin nanoparticle adjuvants incorporating Toll-like receptor agonists drive distinct immune signatures and potent vaccine responses.

Over the past few decades, the development of potent and safe immune-activating adjuvant technologies has become the heart of intensive research in the constant fight against highly mutative and immune evasive viruses such as influenza, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and human immunodeficiency virus (HIV). Herein, we developed a highly modular saponin-based nanoparticle platform incorporating Toll-like receptor agonists (TLRas) including TLR1/2a, TLR4a, and TLR7/8a adjuvants and their mixtures. These various TLRa-saponin nanoparticle adjuvant constructs induce unique acute cytokine and immune-signaling profiles, leading to specific T helper responses that could be of interest depending on the target disease for prevention. In a murine vaccine study, the adjuvants greatly improved the potency, durability, breadth, and neutralization of both COVID-19 and HIV vaccine candidates, suggesting the potential broad application of these adjuvant constructs to a range of different antigens. Overall, this work demonstrates a modular TLRa-SNP adjuvant platform that could improve the design of vaccines and affect modern vaccine development.

Diastereo- and atroposelective synthesis of N-arylpyrroles enabled by light-induced phosphoric acid catalysis.

The C-N axially chiral N-arylpyrrole motifs are privileged scaffolds in numerous biologically active molecules and natural products, as well as in chiral ligands/catalysts. Asymmetric synthesis of N-arylpyrroles, however, is still challenging, and the simultaneous creation of contiguous C-N axial and central chirality remains unknown. Herein, a diastereo- and atroposelective synthesis of N-arylpyrroles enabled by light-induced phosphoric acid catalysis has been developed. The key transformation is a one-pot, three-component oxo-diarylation reaction, which simultaneously creates a C-N axial chirality and a central quaternary stereogenic center. A broad range of unactivated alkynes were readily employed as a reaction partner in this transformation, and the N-arylpyrrole products are obtained in good yields, with excellent enantioselectivities and very good diastereoselectivities. Notably, the N-arylpyrrole skeletons represent interesting structural motifs that could be used as chiral ligands and catalysts in asymmetric catalysis.

Molecular Editing of Pyrroles via a Skeletal Recasting Strategy.

Heterocyclic scaffolds are commonly found in numerous biologically active molecules, therapeutic agents, and agrochemicals. To probe chemical space around heterocycles, many powerful molecular editing strategies have been devised. Versatile C-H functionalization strategies allow for peripheral modifications of heterocyclic motifs, often being specific and taking place at multiple sites. The past few years have seen the quick emergence of exciting "single-atom skeletal editing" strategies, through one-atom deletion or addition, enabling ring contraction/expansion and structural diversification, as well as scaffold hopping. The construction of heterocycles via deconstruction of simple heterocycles is unknown. Herein, we disclose a new molecular editing method which we name the skeletal recasting strategy. Specifically, by tapping on the 1,3-dipolar property of azoalkenes, we recast simple pyrroles to fully substituted pyrroles, through a simple phosphoric acid-promoted one-pot reaction consisting of dearomative deconstruction and rearomative reconstruction steps. The reaction allows for easy access to synthetically challenging tetra-substituted pyrroles which are otherwise difficult to synthesize. Furthermore, we construct N-N axial chirality on our pyrrole products, as well as accomplish a facile synthesis of the anticancer drug, Sutent. The potential application of this method to other heterocycles has also been demonstrated.

Theoretical framework and experimental solution for the air-water interface adsorption problem in cryoEM.

As cryogenic electron microscopy (cryoEM) gains traction in the structural biology community as a method of choice for determining atomic structures of biological complexes, it has been increasingly recognized that many complexes that behave well under conventional negative-stain electron microscopy tend to have preferential orientation, aggregate or simply mysteriously "disappear" on cryoEM grids, but the reasons for such misbehavior are not well understood, limiting systematic approaches to solving the problem. Here, we have developed a theoretical formulation that explains these observations. Our formulation predicts that all particles migrate to the air-water interface (AWI) to lower the total potential surface energy - rationalizing the use of surfactant, which is a direct solution to reducing the surface tension of the aqueous solution. By conducting cryogenic electron tomography (cryoET) with the widely-tested sample, GroEL, we demonstrate that, in a standard buffer solution, nearly all particles migrate to the AWI. Gradual reduction of the surface tension by introducing surfactants decreased the percentage of particles exposed to the surface. By conducting single-particle cryoEM, we confirm that applicable surfactants do not damage the biological complex, thus suggesting that they might offer a practical, simple, and general solution to the problem for high-resolution cryoEM. Application of this solution to a real-world AWI adsorption problem with a more challenging membrane protein, namely, the ClC-1 channel, has led to its first near-atomic structure using cryoEM.

Theoretical framework and experimental solution for the air-water interface adsorption problem in cryoEM.

As cryogenic electron microscopy (cryoEM) gains traction in the structural biology community as a method of choice for determining atomic structures of biological complexes, it has been increasingly recognized that many complexes that behave well under conventional negative-stain electron microscopy tend to have preferential orientation, aggregate or simply mysteriously "disappear" on cryoEM grids. However, the reasons for such misbehavior are not well understood, which limits systematic approaches to solving the problem. Here, we have developed a theoretical formulation that explains these observations. Our formulation predicts that all particles migrate to the air-water interface (AWI) to lower the total potential surface energy-rationalizing the use of surfactant, which is a direct solution to reduce the surface tension of the aqueous solution. By performing cryogenic electron tomography (cryoET) on the widely-tested sample, GroEL, we demonstrate that, in a standard buffer solution, nearly all particles migrate to the AWI. Gradually reducing the surface tension by introducing surfactants decreased the percentage of particles exposed to the surface. By conducting single-particle cryoEM, we confirm that suitable surfactants do not damage the biological complex, thus suggesting that they might provide a practical, simple, and general solution to the problem for high-resolution cryoEM. Applying this solution to a real-world AWI adsorption problem involving a more challenging membrane protein, namely, the ClC-1 channel, has resulted in its near-atomic structure determination using cryoEM.

Tertiary folds of the SL5 RNA from the 5' proximal region of SARS-CoV-2 and related coronaviruses.

Coronavirus genomes sequester their start codons within stem-loop 5 (SL5), a structured, 5' genomic RNA element. In most alpha- and betacoronaviruses, the secondary structure of SL5 is predicted to contain a four-way junction of helical stems, some of which are capped with UUYYGU hexaloops. Here, using cryogenic electron microscopy (cryo-EM) and computational modeling with biochemically-determined secondary structures, we present three-dimensional structures of SL5 from six coronaviruses. The SL5 domain of betacoronavirus SARS-CoV-2, resolved at 4.7 Å resolution, exhibits a T-shaped structure, with its UUYYGU hexaloops at opposing ends of a coaxial stack, the T's "arms." Further analysis of SL5 domains from SARS-CoV-1 and MERS (7.1 and 6.4-6.9 Å resolution, respectively) indicate that the junction geometry and inter-hexaloop distances are conserved features across the studied human-infecting betacoronaviruses. The MERS SL5 domain displays an additional tertiary interaction, which is also observed in the non-human-infecting betacoronavirus BtCoV-HKU5 (5.9-8.0 Å resolution). SL5s from human-infecting alphacoronaviruses, HCoV-229E and HCoV-NL63 (6.5 and 8.4-9.0 Å resolution, respectively), exhibit the same coaxial stacks, including the UUYYGU-capped arms, but with a phylogenetically distinct crossing angle, an X-shape. As such, all SL5 domains studied herein fold into stable tertiary structures with cross-genus similarities, with implications for potential protein-binding modes and therapeutic targets.