Kinetic Analysis of SARS-CoV-2 S1-Integrin Binding Using Live-Cell, Label-Free Optical Biosensing

Kanyó, Nicolett and Borbély, Krisztina and Péter, Beatrix and Kovács, Kinga Dóra and Balogh, Anna and Magyaródi, Beatrix and Kurunczi, Sándor and Székács, Inna and Horváth, Róbert (2025) Kinetic Analysis of SARS-CoV-2 S1-Integrin Binding Using Live-Cell, Label-Free Optical Biosensing. BIOSENSORS, 15 (8). No.-534. ISSN 2079-6374

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Abstract

The SARS-CoV-2 spike (S1) protein facilitates viral entry through binding to angiotensin-converting enzyme 2 (ACE2), but it also contains an Arg–Gly–Asp (RGD) motif that may enable interactions with RGD-binding integrins on ACE2-negative cells. Here, we provide quantitative evidence for this alternative binding pathway using a live-cell, label-free resonant waveguide grating (RWG) biosensor. RWG technology allowed us to monitor real-time adhesion kinetics of live cells to RGD-displaying substrates, as well as cell adhesion to S1-coated surfaces. To characterize the strength of the integrin–S1 interaction, we determined the dissociation constant using two complementary approaches. First, we performed a live-cell competitive binding assay on RGD-displaying surfaces, where varying concentrations of soluble S1 were added to cell suspensions. Second, we recorded the adhesion kinetics of cells on S1-coated surfaces and fitted the data using a kinetic model based on coupled ordinary differential equations. By comparing the results from both methods, we estimate that approximately 33% of the S1 molecules immobilized on the Nb2O5 biosensor surface are capable of initiating integrin-mediated adhesion. These findings support the existence of an alternative integrin-dependent entry route for SARS-CoV-2 and highlight the effectiveness of label-free RWG biosensing for quantitatively probing virus–host interactions under physiologically relevant conditions without the need of the isolation of the interaction partners from the cells.

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