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A recombinant form of the spike (S) glycoprotein S1 domain from severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2), D614G variant was produced by transient transfection in human embryonic kidney HEK293 cells and purified by affinity chromatography. NR-55418 lacks the signal sequence, contains 670 residues of the SARS-CoV-2 S glycoprotein (amino acid residues V16 to R685) and features a C-terminal poly-histidine tag. NR-55418 is a variant of SARS-CoV-2 which contains the D614G mutation in the S glycoprotein as compared to the SARS-CoV-2 reference sequence (GenPept: QHD43416). NR-55418 has a theoretical molecular weight of 76,800 daltons. The crystal structure for the wild-type S glycoprotein from SARS-CoV-2 has been solved at 2.8 ? resolution (PDB: 6VXX).
The S glycoprotein mediates viral binding to the host angiotensin converting enzyme 2 (ACE2). This protein forms a trimer, and when bound to a host receptor allows fusion of the viral and cellular membranes. The D614G mutation is common to the current variants of interest and concern identified by the Centers for Disease Control and Prevention (CDC). This mutation was one of the first documented in the USA in the initial stages of the pandemic after having initially circulated in Europe. Some evidence suggests that variants with the D614G mutation are more infectious than wild-type.
The biological activity of NR-55418 was measured by its binding ability in a functional ELISA, in which immobilized NR-55418 at 2 ?g per mL (100 ?L per well) can bind human ACE2 protein (Fc tag) (ACROBiosystems AC2-H5257); the linear range is 0.2 to 3 ng per mL. Immobilized NR-55418 at 2 ?g
per mL (100 ?L per well) can also bind Anti-SARS-CoV-2 neutralizing antibody (ACROBiosystems SAD-S35); the linear range is 0.2 to 3 ng per mL. The biological activity of NR-55418 was also
measured by its binding ability using biosensor analysis, in which loaded ACROBiosystems AC2-H5257 can bind NR-55418; the affinity constant is 76.4 nM by ForteBio Octet Red96e.
Each vial contains approximately 100 ?g of purified recombinant protein lyophilized in phosphate-buffered saline, pH 7.4 and 10% trehalose.
Additional information and tools are available at ViPR (Virus Pathogen Resource).
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