Structural basis of kindlin-mediated integrin recognition and activation

Abstract

Kindlins and talins are integrin-binding proteins that are critically involved in integrin activation, an essential process for many fundamental cellular activities including cell-matrix adhesion, migration, and proliferation. As FERM-domain-containing proteins, talins and kindlins, respectively, bind different regions of β-integrin cytoplasmic tails. However, compared with the extensively studied talin, little is known about how kindlins specifically interact with integrins and synergistically enhance their activation by talins. Here, we determined crystal structures of kindlin2 in the apo-form and the β1-and β3-integrin bound forms. The apo-structure shows an overall architecture distinct from talins. The complex structures reveal a unique integrin recognition mode of kindlins, which combines two binding motifs to provide specificity that is essential for integrin activation and signaling. Strikingly, our structures uncover an unexpected dimer formation of kindlins. Interrupting dimer formation impairs kindlin-mediated integrin activation. Collectively, the structural, biochemical, and cellular results provide mechanistic explanations that account for the effects of kindlins on integrin activation as well as for how kindlin mutations found in patients with Kindler syndrome and leukocyte-adhesion deficiency may impact integrin-mediated processes.I ntegrins, composed of α-and β-subunits, are the major receptors mediating the cell-extracellular matrix (ECM) adhesion (1-3). By connecting specific ECM proteins and diverse cytoskeletal regulators, integrins mediate bidirectional transmembrane signaling (4, 5). Stable integrin-ECM interaction and subsequent signaling require integrin activation, which was reported to be mediated by talin, a 4.1-protein/ezrin/radixin/moesin (FERM) domain-containing protein (6). Recently, kindlins, another family of FERM-containing proteins, were found to play crucial roles in integrin activation and signaling (7-12).The kindlin family consists of three members in vertebrates, kindlin1/2/3, each containing a FERM domain and a PH domain (Fig. 1A) (13). Compared with the typical FERM domain that consists of three lobes (F1, F2, and F3), kindlin-FERM contains an additional N-terminal F0 lobe. In kindlins, the F1 and F2 lobes are split by a largely unstructured insertion and the PH domain, respectively (Fig. 1A). Kindlins, although sharing high sequence similarity (SI Appendix, Fig. S1), show distinct tissue distributions and nonredundant functions. Kindlin1 is expressed mainly in epithelia, and nonfunctional kindlin1 mutations lead to Kindler syndrome, a congenital skin disease (14-16). Expression of kindlin3 is restricted to the hematopoietic system, and mutations in kindlin3 were found to associate with leukocyte-adhesion deficiency type III (LADIII) (17, 18). Kindlin2 is ubiquitously expressed, and loss of kindlin2 in mice leads to peri-implantation lethality (11). Kindlins are also involved in tumorigenesis and metastasis (19). The kindlin-associated diseases are due, at least in part...

Kindlin supports platelet integrin αIIbβ3 activation by interacting with paxillin

“…A conserved loop in the F 0 subdomain of kindlin-1 is involved in mediating the interaction with PXN and supporting integrin αIIbβ3 activation The F 0 subdomains of kindlins adopt a ubiquitin-like fold (Goult et al, 2009;Li et al, 2017;Perera et al, 2011). To identify the PXN binding sites in kindlin-1 (Fig.…”

“…Because the M3 region is more conserved across the kindlin family members (Fig. 3C) and the M4 is involved in interfacing with the F 1 subdomain in kindlins (Goult et al, 2009;Li et al, 2017), we focused on the M3 region for subsequent studies. When kindlin-1 and the M3 mutant were co-expressed with PXN in CHO-αIIbβ3 cells, we found that the M3 mutant of kindlin-1 exhibited a weaker interaction with PXN compared with its wild-type counterpart (∼65% reduction based on the results from three experiments), although they interacted equally with the β3-integrin (Fig.…”

Kindlin Assists Talin to Promote Integrin Activation

“…The crystal structures of the kindlin2-integrinβ3 and talin1-integrinβ3 complexes revealed the hbond network between the molecules (33). To determine the stability of kindlin2 or talin1integrin complex, we calculated the number of hbonds between integrin CT -kindlin F3 and integrin CT -talin F3.…”

“…In the present study we use the recently solved crystal structure of kindlin (31) to investigate the molecular mechanism of integrin activation through simultaneous binding of talin and kindlin. We use all-atomic microsecond-scale molecular dynamic simulations of αllbβ3 TM/CT structure in an explicit lipid-water environment under the following three conditions: in complex with talin1 F2-F3 subdomains (IT), with kindlin2 (IK), and with both (ITK) to uncover the role of kindlin in integrin activation (Fig.…”

Solution structure of a ubiquitin‐like protein from Trypanosoma brucei

“…The structure of TbUbl11 is comprised of a mostly antiparallel five-stranded β-sheet, which is curling around a central α-helix. The secondary structure elements are as follows: β1 (Residues [15][16][17][18][19], β2 (Residues 24-28), β3 (Residues 58-61), β4 (Residues 64-65), β5 (Residues 83-87), α1 (Residues 35-46), 3 10 helix (Residues 54-56), and α2 (Residues 73-76) [ Fig. 1(d)].…”