Forcing Switch from Short- to Intermediate- and Long-lived States of the αA Domain Generates LFA-1/ICAM-1 Catch Bonds

Abstract

Binding of lymphocyte function-associated antigen-1 (LFA-1) to intercellular adhesion molecule-1 (ICAM-1) mediates leukocyte adhesion under force. Using a biomembrane force probe capable of measuring single bond interactions, we showed ICAM-1 binding to LFA-1 at different conformations, including the bent conformation with the lowest affinity. We quantify how force and conformations of LFA-1 regulate its kinetics with ICAM-1. At zero-force, on-rates were substantially changed by conditions that differentially favor a bent or extended LFA-1 with a closed or open headpiece; but off-rates were identical. With increasing force, LFA-1/ICAM-1 bond lifetimes (reciprocal off-rates) first increased (catch bonds) and then decreased (slip bonds). Three states with distinct off-rates were identified from lifetime distributions. Force shifted the associated fractions from the short-to intermediate-and long-lived states, producing catch bonds at low forces, but increased their off-rates exponentially, converting catch to slip bonds at high forces. An internal ligand antagonist that blocks pulling of the ␣ 7 -helix suppressed the intermediate-/long-lived states and eliminated catch bonds, revealing an internal catch bond between the ␣A and ␤A domains. These results elucidate an allosteric mechanism for the mechanochemistry of LFA-1/ICAM-1 binding.Integrins are membrane molecules broadly expressed on a wide variety of cells as ␣␤ heterodimers that bind ligands on another cell or the extracellular matrix (1, 2). Integrin/ligand interactions are thought to be capable of not only transmitting forces but also transducing signals bi-directionally across the cell membrane, thereby playing a key role in mechanosensing and mechanotransduction (3, 4).Integrins can assume distinct conformations with different ligand binding affinities (1, 2). Several types of conformational changes have been described based on structural (5-8) and functional (9 -14) studies (see below Integrin/ligand bonds are often subjected to forces externally applied to the cell, e.g. during leukocyte adhesion to vascular surfaces, or internally generated by the cell, e.g. during migration. Mechanical forces have been suggested to regulate integrin binding affinity by inducing conformational changes. For example, applying a shear flow to cells has been shown to enhance integrin/ligand binding (12,17,18). Atomic force microscopy single-bond experiments have demonstrated that ␣ 5 ␤ 1 , an ␣A domain-lacking integrin, forms catch bonds with fibronectin (FN) in which force prolongs bond lifetimes in the 10 -30 pN range (19). Steered molecular dynamics simulations have suggested how force might activate integrin ␣A domains (20) and the headpiece of integrin ␣ V ␤ 3 (21-24). However, many mechanistic details about the integrin mechanochemistry are still missing.Using force clamp (25) and thermal fluctuation (26) experiments to measure single bond interactions by a biomembrane force probe (BFP), here we show that lymphocyte functionassociated antigen-1 (LFA-1), an ␣A domain-...

Dynamic control of β1 integrin adhesion by the plexinD1-sema3E axis

“…4C). The generation of a stronger bond under force is consistent with the properties of catch bonds (27). Assay of the α4β1/VCAM-1 bond characteristics under a range of applied forces (Fig.…”

“…Since the initial demonstration of the P-selectin complex binding to PSGL-1 as a catch bond (35), these bonds have been demonstrated for integrins (27,36), actomyosin (37), bacterial adhesion FimH (38), platelet glycoprotein Ibα (39), kinetochore protein (40), cadherin (41), and actin (42). Here we provide a definitive physiologic demonstration of catch bond regulation by a semaphorin signaling through a plexin.…”

Dynamic catch of a Thy-1–α5β1+syndecan-4 trimolecular complex

“…Surprisingly, we find a complex mechanical regulation of adhesive bonds at the single-molecule level: tensile force prolongs the bond lifetime (that is, catch bonds). In contrast to the well-known catch bonds of bimolecular systems, such as cell adhesion receptors (integrins 28,38,39 , selectins 40,41 , glycoprotein Iba 30,42 , E-cadherin 43 and FimH 44 ), the T-cell receptor 31 and cytoskeletal linkages 45,46 , the Thy-1 catch bond is strongly correlated with a bond-stiffening phenotype, termed 'dynamic catch', which partially shifts force to the already engaged but unstretched coreceptor Syn4. Thus, the data reveal a unique, previously unreported class of receptor-ligand bonds whereby force tightens co-receptor engagement that is required for forcemediated adhesion signalling.…”

“…However, the molecular mechanisms by which mechanical force is transduced into biochemical signals remains obscure 27 . Singlemolecule approaches (that is, the biomembrane force probe (BFP)) have been extensively used to study force regulation of protein-protein interactions, determine protein conformational changes and understand signal initiation [28][29][30][31] , dissecting the relative contribution of individual proteins from complex molecular cohorts 32 . For example, single-molecule studies have elucidated the catch bond behaviour-bonds can be stabilized rather than disrupted by force 33,34 .…”

Analyses of movement and contact of two nucleated cells using a gas-driven micropipette aspiration technique

“…A finite element simulation was applied to quantify the effect of the gap distance, indicating a decreased pressure drop inside the pipette (from 98% to 60% when the gap changes from 2 to 0.5 μm on the chosen parameters) (Chen et al, 2010). Since the cell on the right side reported here has the smaller size than the one used in the reference (Chen et al, 2010), it is reasonably supposed that the actual pressure drop is~80-90% of the original pressure drop and that the above equation is still applicable for force and cell movement calculations. Here the suction pressure was given to be 0.3 mm H 2 O and the gas flow rate was varied from 150 to 200 ml/min.…”