Impact of lockdown and unlocking on symptomatology and emergency department visits during the first wave of the COVID-19 pandemic.

Background: The COVID-19 pandemic resulted in a complete nationwide lockdown on March 24, 2020. The months of April and May had stringent lockdown measures followed by a gradual loosening of restrictions in a graded manner.

Methods: This observational study was performed in the emergency department (ED) of a tertiary hospital in south India triage Priority 1 and Priority 2 patients presented during the COVID-19 lockdown and unlock periods spanning from April 2020 to August 2020.

Constitutive phospholipid scramblase activity of a G protein-coupled receptor.

Opsin, the rhodopsin apoprotein, was recently shown to be an ATP-independent flippase (or scramblase) that equilibrates phospholipids across photoreceptor disc membranes in mammalian retina, a process required for disc homoeostasis. Here we show that scrambling is a constitutive activity of rhodopsin, distinct from its light-sensing function. Upon reconstitution into vesicles, discrete conformational states of the protein (rhodopsin, a metarhodopsin II-mimic, and two forms of opsin) facilitated rapid (>10,000 phospholipids per protein per second) scrambling of phospholipid probes.

Atlas of coronavirus replicase structure.

The international response to SARS-CoV has produced an outstanding number of protein structures in a very short time. This review summarizes the findings of functional and structural studies including those derived from cryoelectron microscopy, small angle X-ray scattering, NMR spectroscopy, and X-ray crystallography, and incorporates bioinformatics predictions where no structural data is available. Structures that shed light on the function and biological roles of the proteins in viral replication and pathogenesis are highlighted.

The role of a sodium ion binding site in the allosteric modulation of the A(2A) adenosine G protein-coupled receptor.

The function of G protein-coupled receptors (GPCRs) can be modulated by a number of endogenous allosteric molecules. In this study, we used molecular dynamics, radioligand binding, and thermostability experiments to elucidate the role of the recently discovered sodium ion binding site in the allosteric modulation of the human A(2A) adenosine receptor, conserved among class A GPCRs. While the binding of antagonists and sodium ions to the receptor was noncompetitive in nature, the binding of agonists and sodium ions appears to require mutually exclusive conformational states of the receptor.

Structure of the human glucagon class B G-protein-coupled receptor.

Binding of the glucagon peptide to the glucagon receptor (GCGR) triggers the release of glucose from the liver during fasting; thus GCGR plays an important role in glucose homeostasis. Here we report the crystal structure of the seven transmembrane helical domain of human GCGR at 3.4 Å resolution, complemented by extensive site-specific mutagenesis, and a hybrid model of glucagon bound to GCGR to understand the molecular recognition of the receptor for its native ligand.

Microscale thermophoresis quantifies biomolecular interactions under previously challenging conditions.

Microscale thermophoresis (MST) allows for quantitative analysis of protein interactions in free solution and with low sample consumption. The technique is based on thermophoresis, the directed motion of molecules in temperature gradients. Thermophoresis is highly sensitive to all types of binding-induced changes of molecular properties, be it in size, charge, hydration shell or conformation.

Characterization of lipid matrices for membrane protein crystallization by high-throughput small angle X-ray scattering.

The lipidic cubic phase (LCP) has repeatedly proven to serve as a successful membrane-mimetic matrix for a variety of difficult-to-crystallize membrane proteins. While monoolein has been the predominant lipid of choice, there is a growing need for the characterization and use of other LCP host lipids, allowing exploration of a range of structural parameters such as bilayer thickness and curvature for optimal insertion, stability and crystallogenesis of membrane proteins. Here, we describe the development of a high-throughput (HT) pipeline to employ small angle X-ray scattering (SAXS) - the most direct technique to identify lipid mesophases and measure their structural parameters - to interrogate rapidly a large number of lipid samples under a variety of conditions, similar to those encountered during crystallization.

Structure of the N terminus of cadherin 23 reveals a new adhesion mechanism for a subset of cadherin superfamily members.

The cadherin superfamily encodes more than 100 receptors with diverse functions in tissue development and homeostasis. Classical cadherins mediate adhesion by binding interactions that depend on their N-terminal extracellular cadherin (EC) domains, which swap N-terminal beta-strands. Sequence alignments suggest that the strand-swap binding mode is not commonly used by functionally divergent cadherins.

Serotype-specific structural differences in the protease-cofactor complexes of the dengue virus family.

With an estimated 40% of the world population at risk, dengue poses a significant threat to human health, especially in tropical and subtropical regions. Preventative and curative efforts, such as vaccine development and drug discovery, face additional challenges due to the occurrence of four antigenically distinct serotypes of the causative dengue virus (DEN1 to -4). Complex immune responses resulting from repeat assaults by the different serotypes necessitate simultaneous targeting of all forms of the virus.

Nuclear magnetic resonance structure of the nucleic acid-binding domain of severe acute respiratory syndrome coronavirus nonstructural protein 3.

The nuclear magnetic resonance (NMR) structure of a globular domain of residues 1071 to 1178 within the previously annotated nucleic acid-binding region (NAB) of severe acute respiratory syndrome coronavirus nonstructural protein 3 (nsp3) has been determined, and N- and C-terminally adjoining polypeptide segments of 37 and 25 residues, respectively, have been shown to form flexibly extended linkers to the preceding globular domain and to the following, as yet uncharacterized domain. This extension of the structural coverage of nsp3 was obtained from NMR studies with an nsp3 construct comprising residues 1066 to 1181 [nsp3(1066-1181)] and the constructs nsp3(1066-1203) and nsp3(1035-1181). A search of the protein structure database indicates that the globular domain of the NAB represents a new fold, with a parallel four-strand beta-sheet holding two alpha-helices of three and four turns that are oriented antiparallel to the beta-strands.

Nuclear magnetic resonance structure shows that the severe acute respiratory syndrome coronavirus-unique domain contains a macrodomain fold.

The nuclear magnetic resonance (NMR) structure of a central segment of the previously annotated severe acute respiratory syndrome (SARS)-unique domain (SUD-M, for "middle of the SARS-unique domain") in SARS coronavirus (SARS-CoV) nonstructural protein 3 (nsp3) has been determined. SUD-M(513-651) exhibits a macrodomain fold containing the nsp3 residues 528 to 648, and there is a flexibly extended N-terminal tail with the residues 513 to 527 and a C-terminal flexible tail of residues 649 to 651. As a follow-up to this initial result, we also solved the structure of a construct representing only the globular domain of residues 527 to 651 [SUD-M(527-651)].

Proteomics analysis unravels the functional repertoire of coronavirus nonstructural protein 3.

Severe acute respiratory syndrome (SARS) coronavirus infection and growth are dependent on initiating signaling and enzyme actions upon viral entry into the host cell. Proteins packaged during virus assembly may subsequently form the first line of attack and host manipulation upon infection. A complete characterization of virion components is therefore important to understanding the dynamics of early stages of infection.

International research networks in viral structural proteomics: again, lessons from SARS.

Emerging and re-emerging pathogens and bioterror threats require an organized and coherent response from the worldwide research community to maximize available resources and competencies with the primary goals to understand the pathogen and enable intervention. In 2001, the Structural Proteomics In Europe (SPINE) project prototyped the pan-viral structural genomic approach, and the Severe Acute Respiratory Syndrome (SARS) outbreak in 2003 accelerated the concept of structural characterization of all proteins from a viral proteome and the interaction with their host partners. Following that approach, in 2004 the center for Functional and Structural Proteomics for SARS-CoV related proteins was initiated as part of the US NIH NIAID proteomics resource centers.

Nuclear magnetic resonance structure of the N-terminal domain of nonstructural protein 3 from the severe acute respiratory syndrome coronavirus.

This paper describes the structure determination of nsp3a, the N-terminal domain of the severe acute respiratory syndrome coronavirus (SARS-CoV) nonstructural protein 3. nsp3a exhibits a ubiquitin-like globular fold of residues 1 to 112 and a flexibly extended glutamic acid-rich domain of residues 113 to 183. In addition to the four beta-strands and two alpha-helices that are common to ubiquitin-like folds, the globular domain of nsp3a contains two short helices representing a feature that has not previously been observed in these proteins.

Crystal structure of a monomeric form of severe acute respiratory syndrome coronavirus endonuclease nsp15 suggests a role for hexamerization as an allosteric switch.

Mature nonstructural protein-15 (nsp15) from the severe acute respiratory syndrome coronavirus (SARS-CoV) contains a novel uridylate-specific Mn2+-dependent endoribonuclease (NendoU). Structure studies of the full-length form of the obligate hexameric enzyme from two CoVs, SARS-CoV and murine hepatitis virus, and its monomeric homologue, XendoU from Xenopus laevis, combined with mutagenesis studies have implicated several residues in enzymatic activity and the N-terminal domain as the major determinant of hexamerization. However, the tight link between hexamerization and enzyme activity in NendoUs has remained an enigma.

Ribonucleocapsid formation of severe acute respiratory syndrome coronavirus through molecular action of the N-terminal domain of N protein.

Conserved among all coronaviruses are four structural proteins: the matrix (M), small envelope (E), and spike (S) proteins that are embedded in the viral membrane and the nucleocapsid phosphoprotein (N), which exists in a ribonucleoprotein complex in the lumen. The N-terminal domain of coronaviral N proteins (N-NTD) provides a scaffold for RNA binding, while the C-terminal domain (N-CTD) mainly acts as oligomerization modules during assembly. The C terminus of the N protein anchors it to the viral membrane by associating with M protein.

Crystal structure of nonstructural protein 10 from the severe acute respiratory syndrome coronavirus reveals a novel fold with two zinc-binding motifs.

The severe acute respiratory syndrome coronavirus (SARS-CoV) possesses a large 29.7-kb positive-stranded RNA genome. The first open reading frame encodes replicase polyproteins 1a and 1ab, which are cleaved to generate 16 "nonstructural" proteins, nsp1 to nsp16, involved in viral replication and/or RNA processing.

Structural basis of severe acute respiratory syndrome coronavirus ADP-ribose-1''-phosphate dephosphorylation by a conserved domain of nsP3.

The crystal structure of a conserved domain of nonstructural protein 3 (nsP3) from severe acute respiratory syndrome coronavirus (SARS-CoV) has been solved by single-wavelength anomalous dispersion to 1.4 A resolution. The structure of this "X" domain, seen in many single-stranded RNA viruses, reveals a three-layered alpha/beta/alpha core with a macro-H2A-like fold.

Structural genomics of the severe acute respiratory syndrome coronavirus: nuclear magnetic resonance structure of the protein nsP7.

Here, we report the three-dimensional structure of severe acute respiratory syndrome coronavirus (SARS-CoV) nsP7, a component of the SARS-CoV replicase polyprotein. The coronavirus replicase carries out regulatory tasks involved in the maintenance, transcription, and replication of the coronavirus genome. nsP7 was found to assume a compact architecture in solution, which is comprised primarily of helical secondary structures.

Structure-function relationship of avian eggshell matrix proteins: a comparative study of two major eggshell matrix proteins, ansocalcin and OC-17.

The role of individual matrix proteins in avian eggshell calcification is poorly understood despite numerous attempts to characterize and localize their presence in the eggshell matrix. Ansocalcin, the major matrix protein from goose eggshell, was found to induce the formation of calcite crystal aggregates under in vitro. Owing to its high similarity with the chicken eggshell matrix protein ovocleidin 17 (OC-17), a comparative investigation has been carried out to understand the structure-function relationship.

Assignment of voltage-gated potassium channel blocking activity to kappa-KTx1.3, a non-toxic homologue of kappa-hefutoxin-1, from Heterometrus spinifer venom.

A new family of weak K(+) channel toxins (designated kappa-KTx) with a novel "bi-helical" scaffold has recently been characterized from Heterometrus fulvipes (Scorpionidae) venom. Based on the presence of the minimum functional dyad (Y5 and K19), kappa-hefutoxin-1 (kappa-KTx1.1) was investigated and found to block Kv 1.

Snake venom prothrombin activators similar to blood coagulation factor Xa.

Activation of prothrombin to mature thrombin in vivo occurs by the proteolytic action of the prothrombinase complex consisting of serine proteinase factor Xa, and cofactors that include factor Va, Ca(2+) ions and phospholipids. Several exogenous prothrombin activators are found in snake venom. Among these, Group C prothrombin activators resemble the factor Xa-factor Va complex, while Group D activators are structurally and functionally similar to factor Xa.

Structure of rhodocetin reveals noncovalently bound heterodimer interface.

Rhodocetin is a unique heterodimer consisting of alpha- and beta-subunits of 133 and 129 residues, respectively. The molecule, purified from the crude venom of the Malayan pit viper, Calloselasma rhodostoma, functions as an inhibitor of collagen-induced aggregation. Rhodocetin has been shown to have activity only when present as a dimer.

Trocarin, a blood coagulation factor Xa homologue from snake venom, causes inflammation and mitogenesis.

Trocarin, a Group D prothrombin activator from Tropidechis carinatus snake venom, has high sequence similarity to blood coagulation factor Xa (FXa). Both trocarin and FXa activate prothrombin to mature thrombin and have similar requirements for cofactors, such as factor Va, Ca2+ ions and phospholipids. In addition to its hemostatic functions, human FXa causes inflammation and induces mitogenesis in several cell types due to its interaction with effector protease receptor-1 (EPR-1).

A 1.7A structure of Fve, a member of the new fungal immunomodulatory protein family.

Fve, a major fruiting body protein from Flammulina velutipes, a mushroom possessing immunomodulatory activity, stimulates lymphocyte mitogenesis, suppresses systemic anaphylaxis reactions and edema, enhances transcription of IL-2, IFN-gamma and TNF-alpha, and hemagglutinates red blood cells. It appears to be a lectin with specificity for complex cell-surface carbohydrates. Fve is a non-covalently linked homodimer containing no Cys, His or Met residues.