Single Molecule Study Of Mac-1/ICAM-1 Interaction With Atomic Force Spectroscopy

Mac-1, a member ofβ2 integrin, is mainly expressed on leukocyte and plays a vital part in host defense and immune response. It also presents on the microglia and macrophages of nervous system, and mediates myelin phagocytosis. ICAM-1 belongs to the immunoglobulin superfamily, and mainly expressed on endothelia. As a major ligand of Mac-1, ICAM-1 and Mac-1 have mediated the firm adhesion of leukocyte to endothelia. Mac-1 has an important feature of changing its ligand-binding activity dynamically. It does not adhere to its ligands strongly unless it is activated by stimulation. However, up till now it is known how the increase of ligand-binding ability is realized after Mac-1 activation. The nature of the ligand-binding activity changes that lead to a change in adhesiveness is not understood. In this study, we have applied atomic force microscopy to directly measure the interaction of Mac-1 and ICAM-1. Our results showed that the binding probability and adhesion force of Mac-1 with ICAM-1 increased upon Mac-1 activation. Moreover, by comparing the dynamic force spectra of different Mac-1 mutants, we expected that Mac-1 activation is governed by the downward movement of itsα7 helix.