Single-molecule imaging reveals allosteric stimulation of SARS-CoV-2 spike receptor binding domain by host sialic acid.

Conformational dynamics of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein (S) mediate exposure of the binding site for the cellular receptor, angiotensin-converting enzyme 2 (ACE2). The N-terminal domain (NTD) of S binds terminal sialic acid (SA) moieties on the cell surface, but the functional role of this interaction in virus entry is unknown. Here, we report that NTD-SA interaction enhances both S-mediated virus attachment and ACE2 binding. Through single-molecule Förster resonance energy transfer imaging of individual S trimers, we demonstrate that SA binding to the NTD allosterically shifts the S conformational equilibrium, favoring enhanced exposure of the ACE2-binding site. Antibodies that target the NTD block SA binding, which contributes to their mechanism of neutralization. These findings inform on mechanisms of S activation at the cell surface.

Regulation of Ebola GP conformation and membrane binding by the chemical environment of the late endosome.

Interaction between the Ebola virus envelope glycoprotein (GP) and the endosomal membrane is an essential step during virus entry into the cell. Acidic pH and Ca2+ have been implicated in mediating the GP-membrane interaction. However, the molecular mechanism by which these environmental factors regulate the conformational changes that enable engagement of GP with the target membrane is unknown. Here, we apply fluorescence correlation spectroscopy (FCS) and single-molecule Förster resonance energy transfer (smFRET) imaging to elucidate how the acidic pH, Ca2+ and anionic phospholipids in the late endosome promote GP-membrane interaction, thereby facilitating virus entry. We find that bis(monoacylglycero)phosphate (BMP), which is specific to the late endosome, is especially critical in determining the Ca2+-dependence of the GP-membrane interaction. Molecular dynamics (MD) simulations suggested residues in GP that sense pH and induce conformational changes that make the fusion loop available for insertion into the membrane. We similarly confirm residues in the fusion loop that mediate GP's interaction with Ca2+, which likely promotes local conformational changes in the fusion loop and mediates electrostatic interactions with the anionic phospholipids. Collectively, our results provide a mechanistic understanding of how the environment of the late endosome regulates the timing and efficiency of virus entry.

Interactions between FUS and the C-terminal Domain of Nup62 are Sufficient for their Co-phase Separation into Amorphous Assemblies.

Deficient nucleocytoplasmic transport is emerging as a pathogenic feature of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), including in ALS caused by mutations in Fused in Sarcoma (FUS). Recently, both wild-type and ALS-linked mutant FUS were shown to directly interact with the phenylalanine-glycine (FG)-rich nucleoporin 62 (Nup62) protein, where FUS WT/ Nup62 interactions were enriched within the nucleus but ALS-linked mutant FUS/ Nup62 interactions were enriched within the cytoplasm of cells. Nup62 is a central channel Nup that has a prominent role in forming the selectivity filter within the nuclear pore complex and in regulating effective nucleocytoplasmic transport. Under conditions where FUS phase separates into liquid droplets in vitro, the addition of Nup62 caused the synergistic formation of amorphous assemblies containing both FUS and Nup62. Here, we examined the molecular determinants of this process using recombinant FUS and Nup62 proteins and biochemical approaches. We demonstrate that the structured C-terminal domain of Nup62 containing an alpha-helical coiled-coil region plays a dominant role in binding FUS and is sufficient for inducing the formation of FUS/Nup62 amorphous assemblies. In contrast, the natively unstructured, F/G repeat-rich N-terminal domain of Nup62 modestly contributed to FUS/Nup62 phase separation behavior. Expression of individual Nup62 domain constructs in human cells confirmed that the Nup62 C-terminal domain is essential for localization of the protein to the nuclear envelope. Our results raise the possibility that interactions between FUS and the C-terminal domain of Nup62 can influence the function of Nup62 under physiological and/or pathological conditions.

Regulation of Ebola GP conformation and membrane binding by the chemical environment of the late endosome.

Interaction between the Ebola virus envelope glycoprotein (GP) and the endosomal membrane is an essential step during virus entry into the cell. Acidic pH and Ca2+ have been implicated in mediating the GP-membrane interaction. However, the molecular mechanism by which these environmental factors regulate the conformational changes that enable engagement of GP with the target membrane is unknown. Here, we apply fluorescence correlation spectroscopy (FCS) and single-molecule Forster resonance energy transfer (smFRET) imaging to elucidate how the acidic pH, Ca2+ and anionic phospholipids in the late endosome promote GP-membrane interaction, thereby facilitating virus entry. We find that bis(monoacylglycero)phosphate (BMP), which is specific to the late endosome, is especially critical in determining the Ca2+-dependence of the GP-membrane interaction. Molecular dynamics (MD) simulations suggested residues in GP that sense pH and induce conformational changes that make the fusion loop available for insertion into the membrane. We similarly confirm residues in the fusion loop that mediate GPs interaction with Ca2+, which likely promotes local conformational changes in the fusion loop and mediates electrostatic interactions with the anionic phospholipids. Collectively, our results provide a mechanistic understanding of how the environment of the late endosome regulates the timing and efficiency of virus entry.

Comparison of intramuscular methylergometrine, rectal misoprostol, and low-dose intravenous oxytocin in active management of the third stage of labor.

OBJECTIVE: Active management of the third stage of labor (AMTSL) is a critical intervention for the prevention of postpartum hemorrhage (PPH), which is still the most common cause of maternal morbidity and mortality worldwide. The objective of the study is to compare the effect of intramuscular methylergometrine, rectal misoprostol, and low-dose intravenous oxytocin in the AMTSL in terms of amount of blood loss and duration of the third stage of labor, cost-effectiveness, and side effect profile. MATERIALS AND METHODS: Seventy-five pregnant patients admitted in the maternity ward for vaginal delivery from February 2017 to February 2018 received either intramuscular methylergometrine (0.2 mg) or rectal misoprostol (400 mcg) or low-dose intravenous oxytocin (5 units oxytocin in 100 mL normal saline) for AMTSL. Data were recorded in three groups: Group A (methylergometrine), Group B (misoprostol), and Group C (oxytocin) consisting of 25 cases each. RESULTS: Mean blood loss was found to be least in methylergometrine group (246.87 ± 65.44 mL) as compared to misoprostol (346.13 ± 58.35 mL) and oxytocin (334.5 ± 69.20 mL) (P = 0.000) Mean duration of the third stage of labor was also least in methylergometrine group (6.21 ± 1.58 min) (P = 0.0008). CONCLUSION: Although methylergometrine was found to have higher incidence of side effects such as nausea, vomiting, headache, and raised blood pressure, it was found to be the most effective drug for minimizing blood loss in the third stage of labor. In remote places where healthcare facilities are limited and drugs cannot be administered by parenteral route, rectal misoprostol remains an alternative.

Mitochondrial transit peptide exhibits cell penetration ability and efficiently delivers macromolecules to mitochondria.

Mitochondrial malfunction under various circumstances can lead to a variety of disorders. Effective targeting of macromolecules (drugs) is important for restoration of mitochondrial function and treatment of related disorders. We have designed a novel cell-penetrating mitochondrial transit peptide (CpMTP) for delivery of macromolecules to mitochondria. Comparison between properties of cell-penetrating peptides (CPPs) and mitochondrial signal sequences enabled prediction of peptides with dual ability for cellular translocation and mitochondrial localization. Among the predicted peptides, CpMTP translocates across HeLa cells and shows successful delivery of noncovalently conjugated cargo molecules to mitochondria. CpMTP may have applications in transduction and transfection of mitochondria for therapeutics.

Marine antimicrobial peptide tachyplesin as an efficient nanocarrier for macromolecule delivery in plant and mammalian cells.

Membrane-active peptides can be classified as cell-penetrating peptides and antimicrobial peptides (AMPs) that are known to play interchangeable roles. In this study, this dual behaviour was studied for the marine AMP, tachyplesin. It is a well-established cyclic peptide known to possess antimicrobial properties and was investigated for its cell-penetrating property and cargo delivery ability. Because of its derivation from a marine organism as well as cyclic nature, it has been shown to possess higher stability in vitro. In this study, its internalization as a cell-penetrating peptide was established and characterized in both plant and mammalian systems. It was shown to deliver cargo molecules in both living systems, emerging as an efficient nonviral macromolecule nanocarrier.

Cell penetrating peptides as efficient nanocarriers for delivery of antifungal compound, natamycin for the treatment of fungal keratitis.

PURPOSE: Enhancing the penetration ability of the antifungal drug natamycin, known to possess poor penetration ability through the corneal epithelium, by complexing with cell penetrating peptides. METHODS: The drug, natamycin was conjugated to a cell penetrating peptide, Tat-dimer (Tat2). The uptake ability of the conjugate in human corneal epithelial cells and its antifungal activity against filamentous fungi, F.solani has been elucidated. RESULTS: The cellular penetration ability of natamycin increased upon conjugation with Tat2. The conjugation between natamycin and Tat2 also lead to enhanced solubility of the drug in aqueous medium. The antifungal activity of the conjugate increased two- folds in comparison to unconjugated natamycin against clinical isolates of F.solani. CONCLUSION: The formation of CPP-natamycin complex is clinically significant as it may enhance the bioavailability of natamycin in corneal tissues and aid in efficient management of fungal keratitis.

In silico studies in probing the role of kinetic and structural effects of different drugs for the reactivation of tabun-inhibited AChE.

We have examined the reactivation mechanism of the tabun-conjugated AChE with various drugs using density functional theory (DFT) and post-Hartree-Fock methods. The electronic environments and structural features of neutral oximes (deazapralidoxime and 3-hydroxy-2-pyridinealdoxime) and charged monopyridinium oxime (2-PAM) and bispyridinium oxime (Ortho-7) are different, hence their efficacy varies towards the reactivation process of tabun-conjugated AChE. The calculated potential energy surfaces suggest that a monopyridinium reactivator is less favorable for the reactivation of tabun-inhibited AChE compared to a bis-quaternary reactivator, which substantiates the experimental study. The rate determining barrier with neutral oximes was found to be ∼2.5 kcal/mol, which was ∼5.0 kcal/mol lower than charged oxime drugs such as Ortho-7. The structural analysis of the calculated geometries suggest that the charged oximes form strong O(…)H and N(…)H hydrogen bonding and C-H(…)π non-bonding interaction with the tabun-inhibited enzyme to stabilize the reactant complex compared to separated reactants, which influences the activation barrier. The ability of neutral drugs to cross the blood-brain barrier was also found to be superior to charged antidotes, which corroborates the available experimental observations. The calculated activation barriers support the superiority of neutral oximes for the activation of tabun-inhibited AChE compared to charged oximes. However, they lack effective interactions with their peripheral sites. Docking studies revealed that the poor binding affinity of simple neutral oxime drugs such as 3-hydroxy-2-pyridinealdoxime inside the active-site gorge of AChE was significantly augmented with the addition of neutral peripheral units compared to conventional charged peripheral sites. The newly designed oxime drug 2 appears to be an attractive candidate as efficient antidote to kinetically and structurally reactivate the tabun-inhibited enzyme.

Microbial synthetic biology for human therapeutics.

The emerging field of synthetic biology holds tremendous potential for developing novel drugs to treat various human conditions. The current study discusses the scope of synthetic biology for human therapeutics via microbial approach. In this context, synthetic biology aims at designing, engineering and building new microbial synthetic cells that do not pre-exist in nature as well as re-engineer existing microbes for synthesis of therapeutic products. It is expected that the construction of novel microbial genetic circuitry for human therapeutics will greatly benefit from the data generated by 'omics' approaches and multidisciplinary nature of synthetic biology. Development of novel antimicrobial drugs and vaccines by engineering microbial systems are a promising area of research in the field of synthetic biology for human theragnostics. Expression of plant based medicinal compounds in the microbial system using synthetic biology tools is another avenue dealt in the present study. Additionally, the study suggest that the traditional medicinal knowledge can do value addition for developing novel drugs in the microbial systems using synthetic biology tools. The presented work envisions the success of synthetic biology for human therapeutics via microbial approach in a holistic manner. Keeping this in view, various legal and socio-ethical concerns emerging from the use of synthetic biology via microbial approach such as patenting, biosafety and biosecurity issues have been touched upon in the later sections.