Single-molecule Force Spectroscopy on Biomembrane Force Probe to Characterize Force-dependent Bond Lifetimes of Receptor–ligand Interactions on Living Cells

The transmembrane receptor-ligand interactions play a vital role in the physiological and pathological processes of living cells, such as immune cell activation, neural synapse formation, or viral invasion into host cells. Mounting evidence suggests that these processes involve mechanosensing and mechanotransduction, which are directly mediated by the force-dependent transmembrane receptor-ligand interactions. Some single-molecule force spectroscopy techniques have been applied to investigate force-dependent kinetics of receptor-ligand interactions. Among these, the biomembrane force probe (BFP), a unique and powerful technique, can quantitatively and accurately determine the force-dependent parameters of transmembrane receptor-ligand interactions at the single-molecule level on living cells. The stiffness, spatial resolution, force, and bond lifetime range of BFP are 0.1-3 pN/nm, 2-3 nm, 1-10 pN, and 5 × 10 -200 s, respectively. Therefore, this technique is very suitable for studying transient and weak interactions between transmembrane receptors and their ligands. Here, we share in detail the in situ characterization of the single-molecule force-dependent bond lifetime of transmembrane receptor-ligand interactions, based on a force-clamp assay with BFP.