Structural studies on full-length talin1 reveal a compact auto-inhibited dimer: Implications for talin activation

Abstract

Talin is a large adaptor protein that activates integrins and couples them to cytoskeletal actin. Talin contains an N-terminal FERM (band 4.1, ezrin, radixin, moesin) domain (the head) linked to a flexible rod comprised of 13 amphipathic helical bundles (R1–R13) that terminate in a C-terminal helix (DD) that forms an anti-parallel dimer. We derived a three-dimensional structural model of full-length talin at a resolution of approximately 2.5 nm using EM reconstruction of full-length talin and the known shapes of the individual domains and inter-domain angles as derived from small angle X-ray scattering. Talin adopts a compact conformation consistent with a dimer in which the two talin rods form a donut-shaped structure, with the two talin heads packed side by side occupying the hole at the center of this donut. In this configuration, the integrin binding site in the head domain and the actin-binding site at the carboxy-terminus of the rod are masked, implying that talin must unravel before it can support integrin activation and engage the actin cytoskeleton.

Talin determines the nanoscale architecture of focal adhesions

“…4). Interestingly, the length of talin/L432G corresponds to ∼81 nm (21 nm/sin 15°), in good agreement with the recent estimate of the end-to-end length of talin in which all domains are folded (35). We surmise that the increased length of ∼16 nm observed in cells expressing wild-type talin could be due to their greater contractility relative to talin/L432G cells, which may lead to a partial unfolding of rod domains.…”

“…S4A). Recent structural studies suggest that individual domains of the talin rod are highly modular (35), permitting us to generate "minitalins" analogs that vary in sequence from 29 to 58% of full-length talin. We refer to these by their nominal sequence lengths, e.g., T29 for the analog that contains 29% of the sequence of full-length talin (T100), and so on ( Fig.…”

Talin – the master of integrin adhesions

“…Electron microscopy observations have suggested that cytoplasmic talin is in a closed conformation (Molony and Burridge, 1985), and cryo-electron microscopy was used to generate a rolled-up dimer model, with talin heads packed at the centre of a doughnut-shaped structure that is unable to bind integrins (Goult et al, 2013a). Two intramolecular interactions between the head and rod have been mapped: between R9 and F3, masking IBS1 (Goksoy et al, 2008;Goult et al, 2009;Zhang et al, 2016), and between R1-R2 and F2-F3, potentially masking membranebinding regions of talin head (Banno et al, 2012).…”

“…The FERM domain of talin is atypical in that the first of the characteristic three subdomains (F1) is duplicated, adding a fourth subdomain at the N-terminus (F0) , a feature only shared with kindlins. The head is followed by an unstructured region (the 'linker'; ∼80 amino acids) and then the rod domain (∼2000 amino acids), which is formed of 13 helical bundle domains (R1-R13, containing 62 α-helices) each consisting of four or five α-helices Goult et al, 2013a). In some non-vertebrate organisms, talin has additional sequences beyond the 62nd helix; for example, Dictyostelium talin B contains a villin headpiece-like domain (Tsujioka et al, 1999), and a Drosophila variant extends talin by ∼300 amino acids (Senetar and McCann, 2005).…”

Protein conformation as a regulator of cell–matrix adhesion

“…A recent study suggests that talin adopts a donut-shaped structure in its auto-inhibited state 114 ( Fig. 2).…”