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1.
JCI Insight ; 6(13)2021 07 08.
Article in English | MEDLINE | ID: covidwho-1301767

ABSTRACT

BACKGROUNDThe role of humoral immunity in COVID-19 is not fully understood, owing, in large part, to the complexity of antibodies produced in response to the SARS-CoV-2 infection. There is a pressing need for serology tests to assess patient-specific antibody response and predict clinical outcome.METHODSUsing SARS-CoV-2 proteome and peptide microarrays, we screened 146 COVID-19 patients' plasma samples to identify antigens and epitopes. This enabled us to develop a master epitope array and an epitope-specific agglutination assay to gauge antibody responses systematically and with high resolution.RESULTSWe identified linear epitopes from the spike (S) and nucleocapsid (N) proteins and showed that the epitopes enabled higher resolution antibody profiling than the S or N protein antigen. Specifically, we found that antibody responses to the S-811-825, S-881-895, and N-156-170 epitopes negatively or positively correlated with clinical severity or patient survival. Moreover, we found that the P681H and S235F mutations associated with the coronavirus variant of concern B.1.1.7 altered the specificity of the corresponding epitopes.CONCLUSIONEpitope-resolved antibody testing not only affords a high-resolution alternative to conventional immunoassays to delineate the complex humoral immunity to SARS-CoV-2 and differentiate between neutralizing and non-neutralizing antibodies, but it also may potentially be used to predict clinical outcome. The epitope peptides can be readily modified to detect antibodies against variants of concern in both the peptide array and latex agglutination formats.FUNDINGOntario Research Fund (ORF) COVID-19 Rapid Research Fund, Toronto COVID-19 Action Fund, Western University, Lawson Health Research Institute, London Health Sciences Foundation, and Academic Medical Organization of Southwestern Ontario (AMOSO) Innovation Fund.


Subject(s)
Agglutination Tests/methods , Antibody Formation/immunology , COVID-19 Serological Testing/methods , COVID-19/immunology , Epitopes, B-Lymphocyte/immunology , SARS-CoV-2/immunology , Amino Acid Sequence , Antibodies, Neutralizing/blood , Antibodies, Neutralizing/immunology , Antibodies, Viral/blood , Antibodies, Viral/immunology , Antibody Specificity/immunology , COVID-19/blood , COVID-19/mortality , Epitopes/immunology , Epitopes, B-Lymphocyte/chemistry , Epitopes, B-Lymphocyte/genetics , Humans , Immunity, Humoral , Microarray Analysis/methods , Nucleocapsid/chemistry , Nucleocapsid/genetics , Nucleocapsid/immunology , Peptides/immunology , SARS-CoV-2/genetics , Severity of Illness Index , Spike Glycoprotein, Coronavirus/chemistry , Spike Glycoprotein, Coronavirus/genetics , Spike Glycoprotein, Coronavirus/immunology
2.
SLAS Discov ; 26(9): 1200-1211, 2021 10.
Article in English | MEDLINE | ID: covidwho-1290310

ABSTRACT

The COVID-19 pandemic has clearly brought the healthcare systems worldwide to a breaking point, along with devastating socioeconomic consequences. The SARS-CoV-2 virus, which causes the disease, uses RNA capping to evade the human immune system. Nonstructural protein (nsp) 14 is one of the 16 nsps in SARS-CoV-2 and catalyzes the methylation of the viral RNA at N7-guanosine in the cap formation process. To discover small-molecule inhibitors of nsp14 methyltransferase (MTase) activity, we developed and employed a radiometric MTase assay to screen a library of 161 in-house synthesized S-adenosylmethionine (SAM) competitive MTase inhibitors and SAM analogs. Among six identified screening hits, SS148 inhibited nsp14 MTase activity with an IC50 value of 70 ± 6 nM and was selective against 20 human protein lysine MTases, indicating significant differences in SAM binding sites. Interestingly, DS0464 with an IC50 value of 1.1 ± 0.2 µM showed a bisubstrate competitive inhibitor mechanism of action. DS0464 was also selective against 28 out of 33 RNA, DNA, and protein MTases. The structure-activity relationship provided by these compounds should guide the optimization of selective bisubstrate nsp14 inhibitors and may provide a path toward a novel class of antivirals against COVID-19, and possibly other coronaviruses.


Subject(s)
COVID-19/genetics , Exoribonucleases/genetics , Protein Binding/genetics , SARS-CoV-2/genetics , Viral Nonstructural Proteins/genetics , Antiviral Agents/pharmacology , Binding Sites/genetics , COVID-19/virology , Humans , Methylation , Pandemics , RNA, Viral/genetics , SARS-CoV-2/pathogenicity , Virus Replication/genetics
3.
SLAS Discov ; 26(6): 757-765, 2021 07.
Article in English | MEDLINE | ID: covidwho-1194439

ABSTRACT

Frequent outbreaks of novel coronaviruses (CoVs), highlighted by the current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, necessitate the development of therapeutics that could be easily and effectively administered worldwide. The conserved mRNA-capping process enables CoVs to evade their host immune system and is a target for antiviral development. Nonstructural protein (nsp) 16 in complex with nsp10 catalyzes the final step of coronaviral mRNA capping through its 2'-O-methylation activity. Like other methyltransferases, the SARS-CoV-2 nsp10-nsp16 complex is druggable. However, the availability of an optimized assay for high-throughput screening (HTS) is an unmet need. Here, we report the development of a radioactivity-based assay for the methyltransferase activity of the nsp10-nsp16 complex in a 384-well format, kinetic characterization, and optimization of the assay for HTS (Z' factor = 0.83). Considering the high conservation of nsp16 across known CoV species, the potential inhibitors targeting the SARS-CoV-2 nsp10-nsp16 complex may also be effective against other emerging pathogenic CoVs.


Subject(s)
Adenosine/analogs & derivatives , High-Throughput Screening Assays , RNA Caps/antagonists & inhibitors , RNA, Viral/antagonists & inhibitors , Viral Nonstructural Proteins/antagonists & inhibitors , Viral Regulatory and Accessory Proteins/antagonists & inhibitors , Adenosine/chemistry , Adenosine/pharmacology , COVID-19/virology , Cloning, Molecular , Enzyme Assays , Enzyme Inhibitors/chemistry , Enzyme Inhibitors/pharmacology , Escherichia coli/genetics , Escherichia coli/metabolism , Gene Expression , Genetic Vectors/chemistry , Genetic Vectors/metabolism , Humans , Kinetics , Methylation , Methyltransferases , Models, Molecular , RNA Caps/genetics , RNA Caps/metabolism , RNA, Viral/genetics , RNA, Viral/metabolism , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , SARS-CoV-2/drug effects , SARS-CoV-2/enzymology , SARS-CoV-2/genetics , Tritium , Viral Nonstructural Proteins/chemistry , Viral Nonstructural Proteins/genetics , Viral Nonstructural Proteins/metabolism , Viral Regulatory and Accessory Proteins/chemistry , Viral Regulatory and Accessory Proteins/genetics , Viral Regulatory and Accessory Proteins/metabolism
4.
SLAS Discov ; 26(5): 620-627, 2021 06.
Article in English | MEDLINE | ID: covidwho-1021348

ABSTRACT

SARS-CoV-2, the coronavirus that causes COVID-19, evades the human immune system by capping its RNA. This process protects the viral RNA and is essential for its replication. Multiple viral proteins are involved in this RNA capping process, including the nonstructural protein 16 (nsp16), which is an S-adenosyl-l-methionine (SAM)-dependent 2'-O-methyltransferase. Nsp16 is significantly active when in complex with another nonstructural protein, nsp10, which plays a key role in its stability and activity. Here we report the development of a fluorescence polarization (FP)-based RNA displacement assay for nsp10-nsp16 complex in a 384-well format with a Z' factor of 0.6, suitable for high-throughput screening. In this process, we purified the nsp10-nsp16 complex to higher than 95% purity and confirmed its binding to the methyl donor SAM, the product of the reaction, S-adenosyl-l-homocysteine (SAH), and a common methyltransferase inhibitor, sinefungin, using isothermal titration calorimetry (ITC). The assay was further validated by screening a library of 1124 drug-like compounds. This assay provides a cost-effective high-throughput method for screening the nsp10-nsp16 complex for RNA competitive inhibitors toward developing COVID-19 therapeutics.


Subject(s)
Antiviral Agents/pharmacology , High-Throughput Screening Assays , RNA, Viral/antagonists & inhibitors , SARS-CoV-2/drug effects , Small Molecule Libraries/pharmacology , Viral Nonstructural Proteins/antagonists & inhibitors , Viral Regulatory and Accessory Proteins/antagonists & inhibitors , Adenosine/analogs & derivatives , Adenosine/pharmacology , Binding, Competitive , COVID-19/drug therapy , COVID-19/virology , Enzyme Inhibitors/pharmacology , Fluorescence Polarization , Gene Expression Regulation , Host-Pathogen Interactions/drug effects , Humans , Methyltransferases , Protein Binding , RNA Caps/antagonists & inhibitors , RNA Caps/genetics , RNA Caps/metabolism , RNA, Viral/genetics , RNA, Viral/metabolism , SARS-CoV-2/genetics , SARS-CoV-2/metabolism , Signal Transduction , Viral Nonstructural Proteins/genetics , Viral Nonstructural Proteins/metabolism , Viral Regulatory and Accessory Proteins/genetics , Viral Regulatory and Accessory Proteins/metabolism , Virus Replication
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