In recent years, special interests have been centralized on specific receptor/ligand interaction of single molecules, which play an important role in the processes of cell adhesion and antigen recognition1,2. By quantitatively measuring the external force that induced dissociation of the receptor/ligand bond, specific binding properties—such as binding strength, thermal off-rate, binding energy and binding length—can be obtained3,4,5.
Apolipoprotein A-I (ApoA-I) has been found to be anti-atherogenic by facilitating cellular lipids efflux from peripheral tissues to the liver and promoting reverse cholesterol transport (RCT) through the interaction with ATP binding cassette transporter A1 (ABCA1)6,7,8. However, mechanism of that interaction is still unknown on the single-bond level due to lack of appropriate high resolving measuring techniques9.
Here, for the first time, the binding strength of dysfunctional apoA-I/ABCA1 has been analyzed by single-molecule force spectroscopy. Taking advantage of the optical tweezers system we set up, high-resolution measurement of the bonds’ rupture force was performed on single living THP-1 cells, revealing that the purified dysfunctional apoA-I specifically interacts with ABCA1 through two binding sites on the cell surface with strength of 26.5±4.9 pN and 56.7±4.1 pN, respectively. The higher capacity site corresponds to a lower binding strength, while the lower capacity site has a higher strength, which agrees with the pathophysiologic results.
Moreover, through control test with anti-ABCA1 antibody we found that the anti-ABCA1 antibody only targets at the higher capacity site, suggesting that it is possible to implement fast drug screening by measuring the specific receptor/ligand interaction there on single living cells.