The SARS-CoV-2 virus binds to host cell surface ACE2 on the plasma membrane via the spike protein's receptor binding domain. Our work has resulted in the generation of a versatile imaging probe using recombinant Spike receptor binding domain conjugated to fluorescent quantum dots (QDs). This probe is capable of engaging in energy transfer quenching with ACE2-conjugated gold nanoparticles enabling biochemical monitoring of binding. Neutralizing antibodies and recombinant human ACE2 blocked quenching, demonstrating a specific binding interaction. In cell-based assays, we observed immediate binding of the probe on the cell surface of ACE2-expressing cells followed by endocytosis. Neutralizing antibodies and ACE2-Fc fully prevented binding and endocytosis with low nanomolar potency. Importantly, we can use this QD nanoparticle probe to identify and validate inhibitors of the SARS-CoV-2 Spike and ACE2 receptor binding in human cells. This work enables facile, rapid, and high-throughput biochemical- and cell-based screening of inhibitors for coronavirus Spike-mediated cell recognition and entry.
Quantum Dot-Conjugated SARS-CoV-2 Spike Nanoparticles for SARS-CoV-2 infection modeling and drug discovery