Structural Basis of Integrin Activation by Talin

Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, England, UK.
Cell (Impact Factor: 32.24). 02/2007; 128(1):171-82. DOI: 10.1016/j.cell.2006.10.048
Source: PubMed


Regulation of integrin affinity (activation) is essential for metazoan development and for many pathological processes. Binding of the talin phosphotyrosine-binding (PTB) domain to integrin beta subunit cytoplasmic domains (tails) causes activation, whereas numerous other PTB-domain-containing proteins bind integrins without activating them. Here we define the structure of a complex between talin and the membrane-proximal integrin beta3 cytoplasmic domain and identify specific contacts between talin and the integrin tail required for activation. We used structure-based mutagenesis to engineer talin and beta3 variants that interact with comparable affinity to the wild-type proteins but inhibit integrin activation by competing with endogenous talin. These results reveal the structural basis of talin's unique ability to activate integrins, identify an interaction that could aid in the design of therapeutics to block integrin activation, and enable engineering of cells with defects in the activation of multiple classes of integrins.

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    • "The retention of slow rolling also suggests that shear forces applied to L2- ICAM-1 bonds are sufficient for integrin extension (Chen et al., 2012). In static systems, the L325R mutation prevents the talin-induced tilting of the 3 transmembrane domain required for allosteric activation of IIb3 (Wegener et al., 2007; Kim et al., 2012). Our finding that talin binding to the MP domain of the  subunit, which is blocked by the L325R mutation, is required for arrest indicates that the forces experienced during slow rolling are not sufficient to cause the headpiece opening associated with neutrophil arrest, even in the presence of chemokines. "
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    ABSTRACT: Neutrophil recruitment, mediated by β2 integrins, combats pyogenic infections but also plays a key role in ischemia-reperfusion injury and other inflammatory disorders. Talin induces allosteric rearrangements in integrins that increase affinity for ligands (activation). Talin also links integrins to actin and other proteins that enable formation of adhesions. Structural studies have identified a talin1 mutant (L325R) that perturbs activation without impairing talin's capacity to link integrins to actin and other proteins. Here, we found that mice engineered to express only talin1(L325R) in myeloid cells were protected from renal ischemia-reperfusion injury. Dissection of neutrophil function in vitro and in vivo revealed that talin1(L325R) neutrophils had markedly impaired chemokine-induced, β2 integrin-mediated arrest, spreading, and migration. Surprisingly, talin1(L325R) neutrophils exhibited normal selectin-induced, β2 integrin-mediated slow rolling, in sharp contrast to the defective slow rolling of neutrophils lacking talin1 or expressing a talin1 mutant (W359A) that blocks talin interaction with integrins. These studies reveal the importance of talin-mediated activation of integrins for renal ischemia-reperfusion injury. They further show that neutrophil arrest requires talin recruitment to and activation of integrins. However, although neutrophil slow rolling requires talin recruitment to integrins, talin-mediated integrin activation is dispensable. © 2015 Yago et al.
    Journal of Experimental Medicine 07/2015; 210(2). DOI:10.1084/jem.20142358 · 12.52 Impact Factor
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    • "(B) Structure of talin2 F2-F3 (yellow) aligned with the F2-F3 domains of talin1 from PDB 1MK9 (cyan) (Garcia-Alvarez et al, 2003). (C) Structure of β1D (red) bound to talin2 F2-F3 (yellow) aligned to the structure of the β3/PIPK1γ peptide (magenta) bound to talin1 F3 (cyan) from PDB 2H7E (Wegener et al, 2007). The alignment used the backbone of the talin1 F3 domain. "

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    • "A major intracellular player known to contribute to integrin function regulation and activation is Talin1 [24], [27]–[30]. Talin1 is a cytoplasmic protein that mediates the link between LFA-1 and the cytoskeleton by binding the β2 subunit of LFA-1 to actin [32], [33]. Since we here observed major changes in the fraction of stationary, cytoskeleton bound LFA-1 molecules between monocytes and mDCs, and between mDCs before and after CCL21 activation and ligand binding, we next sought to investigate the involvement of Talin1 in this difference. "
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    ABSTRACT: LFA-1 is a leukocyte specific β2 integrin that plays a major role in regulating adhesion and migration of different immune cells. Recent data suggest that LFA-1 on mature dendritic cells (mDCs) may function as a chemokine-inducible anchor during homing of DCs through the afferent lymphatics into the lymph nodes, by transiently switching its molecular conformational state. However, the role of LFA-1 mobility in this process is not yet known, despite that the importance of lateral organization and dynamics for LFA-1-mediated adhesion regulation is broadly recognized. Using single particle tracking approaches we here show that LFA-1 exhibits higher mobility on resting mDCs compared to monocytes. Lymphoid chemokine CCL21 stimulation of the LFA-1 high affinity state on mDCs, led to a significant reduction of mobility and an increase on the fraction of stationary receptors, consistent with re-activation of the receptor. Addition of soluble monomeric ICAM-1 in the presence of CCL21 did not alter the diffusion profile of LFA-1 while soluble ICAM-1 nano-aggregates in the presence of CCL21 further reduced LFA-1 mobility and readily bound to the receptor. Overall, our results emphasize the importance of LFA-1 lateral mobility across the membrane on the regulation of integrin activation and its function as adhesion receptor. Importantly, our data show that chemokines alone are not sufficient to trigger the high affinity state of the integrin based on the strict definition that affinity refers to the adhesion capacity of a single receptor to its ligand in solution. Instead our data indicate that nanoclustering of the receptor, induced by multi-ligand binding, is required to maintain stable cell adhesion once LFA-1 high affinity state is transiently triggered by inside-out signals.
    PLoS ONE 06/2014; 9(6):e99589. DOI:10.1371/journal.pone.0099589 · 3.23 Impact Factor
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