The Structure of the Talin Head Reveals a Novel Extended Conformation of the FERM Domain

Abstract

SummaryFERM domains are found in a diverse superfamily of signaling and adaptor proteins at membrane interfaces. They typically consist of three separately folded domains (F1, F2, F3) in a compact cloverleaf structure. The crystal structure of the N-terminal head of the integrin-associated cytoskeletal protein talin reported here reveals a novel FERM domain with a linear domain arrangement, plus an additional domain F0 packed against F1. While F3 binds β-integrin tails, basic residues in F1 and F2 are required for membrane association and for integrin activation. We show that these same residues are also required for cell spreading and focal adhesion assembly in cells. We suggest that the extended conformation of the talin head allows simultaneous binding to integrins via F3 and to PtdIns(4,5)P2-enriched microdomains via basic residues distributed along one surface of the talin head, and that these multiple interactions are required to stabilize integrins in the activated state.

A novel membrane-dependent on/off switch mechanism of talin FERM domain at sites of cell adhesion

“…The effect of IP4 was more pronounced than that with IP3, presumably due to the additional negatively charged phosphate group. Both IP3 and IP4 are quite selective, because, under the same conditions, neither perturbed talin-F0F1 (Supplementary information, Figure S3A), which also has positively charged surface for potential interaction with membranes [16]. This specificity is consistent with the talin-F2F3 being the major fragment for the lipid binding [14].…”

“…As mentioned above, talin-FERM contains a stretch of positively charged surface that associates with membrane to promote the talin-F3/β integrin-MPCT interaction [13][14][15][16][17]. Figure 1D (left panel) provides the detailed illustration of the positively charged surface in talin-F2F3, which mainly involves K268, K272, K274, R277, and K278 in talin-F2, and K322 and K324 in talin-F3.…”

“…Structural and biochemical analyses have shown that the talin-FERM binding to integrin β CT triggers the separation of a key integrin α/β CT clasp, thus facilitating the global conformational change and activation of the receptor [7,8,13]. Stretches of positively charged surfaces on F1, F2, and F3 were also found to be crucial for this process by targeting talin-FERM to the membrane and enhancing the talin-FERM/integrin β CT interaction [13][14][15][16][17]. However, how the membrane-targeting and integrin binding of talin-FERM are spatiotemporally regulated to control the dynamics of integrin adhesion is not understood.…”

“…Membrane lipid phosphotidylinositol-4,5-bisphosphate (PIP2) [19,21], which is locally enriched by talin-recruited PIPKIγ kinase [22,23], was shown to activate talin [19,21] and promote integrin-mediated cell adhesion [15,[24][25][26][27][28], but the detailed structural basis of this is not clear. The prevailing hypothesis is that PIP2 may sterically induce the conformational change of talin [2,15,16,19,21], a mechanism widely employed in the known PIP2-mediated activation of proteins, including FERM domain proteins [29,30].…”

The tale of two talins – two isoforms to fine‐tune integrin signalling

“…Moreover, the crystal structure of the talin1 FERM domain shows a linear domain structure 47 rather than the cloverleaf structure found in other FERM domain proteins. The structure of the talin2 FERM domain confirms this linear domain arrangement (our unpublished data).…”