Structural basis of the interaction between integrin alpha6beta4 and plectin at the hemidesmosomes - PubMed (original) (raw)

Structural basis of the interaction between integrin alpha6beta4 and plectin at the hemidesmosomes

José M de Pereda et al. EMBO J. 2009.

Abstract

The interaction between the integrin alpha6beta4 and plectin is essential for the assembly and stability of hemidesmosomes, which are junctional adhesion complexes that anchor epithelial cells to the basement membrane. We describe the crystal structure at 2.75 A resolution of the primary alpha6beta4-plectin complex, formed by the first pair of fibronectin type III domains and the N-terminal region of the connecting segment of beta4 and the actin-binding domain of plectin. Two missense mutations in beta4 (R1225H and R1281W) linked to nonlethal forms of epidermolysis bullosa prevent essential intermolecular contacts. We also present two structures at 1.75 and 2.05 A resolution of the beta4 moiety in the absence of plectin, which reveal a major rearrangement of the connecting segment of beta4 on binding to plectin. This conformational switch is correlated with the way alpha6beta4 promotes stable adhesion or cell migration and suggests an allosteric control of the integrin.

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Figures

Figure 1

Figure 1

Structure of the integrin β4–plectin complex. (A) Schematic representation of the domain organisation of plectin and the cytoplasmic domains of integrin α6β4. The regions of both proteins corresponding to the primary interaction site, whose crystal structure is presented herein, are highlight by a yellow box. (B) Ribbon representation in two orthogonal views of the integrin β4 (residues 1127–1318 in blue and 1324–1330 in orange) bound to plectin (residues 60–290 in red), with secondary structure elements labelled. Molecular figures were prepared using PyMOL (Delano, 2002).

Figure 2

Figure 2

Integrin β4–plectin interface. (A) Open-book view of the complex. Ribbon representation of the β4 (left) and plectin (right) structure with residues that constitute the interface shown as sticks. (B, C) Surface representation coloured by electrostatic potential (from -12 kT/e in red to 12 kT/e in blue) of β4 (B) and plectin (C) in the same orientation as in (A). Residues that form part of the interfaces are labelled on each surface. The backbone of the companion partner is partially shown as a wire, with the side chains that participate in the interaction shown as sticks and labelled with arrows.

Figure 3

Figure 3

Structure of the N-terminal arm of plectin. (A) Representation of the N-terminal arm of plectin (red) bound to the FnIII-2 of β4 (blue). An omit map (2mFobs-DFcalc, contoured at 1σ) is shown in blue; the map was calculated after simulated annealing refinement of a model in which the plectin arm was omitted. (B) Cα-trace of the N-terminal region of ABD in the absence of plectin (orange, PDB 1MB8) superimposed on the structure of the ABD (red) bound to β4 (blue). (C) Comparison of the sequences of plectin 1C and 1A upstream of the ABD. Only the initial residues of the CH1, which is common to the two isoforms, are shown. The secondary structure elements in the free (orange) and β4-bound (red) structures of the ABD are shown on top.

Figure 4

Figure 4

Structural basis of missense mutations of β4 linked to epidermolysis bullosa. (A) Close-up showing the intermolecular contacts between R1225 of β4 (blue) and plectin (red). A hypothetical conformation of the His side chain in the R1225H mutant is shown to illustrate the effect of this substitution, which prevents the interactions with N146, R148 and D151 in plectin. (B) Detailed view of the contacts established by R1281 of β4, and nearby residues (coloured as in A). A possible structure of the Trp side chain in the disease-linked mutation R1281W is shown. The imidazole ring does not maintain the H-bonds established by R1281 and most likely it causes steric clashes with W1240 of β4 and P157 of plectin.

Figure 5

Figure 5

Conformational change of the connecting segment of β4 between the free and plectin-bound structures. (A) Ribbon representation of the 1126–1348 free β4 structure, with the FnIII-2 in blue and the CS in orange (the FnIII-1 has been omitted in all panels for clarity). The Pro-rich loop (residues 1324–1338), for which no electron density was observed, is shown as a dotted line. (B) Representation of the 1126–1339 free β4 structure in the same orientation and colouring as in (A). (C) Detailed view of the CS (shown as sticks, orange) in the 1126–1339 free β4 structure. P1323, P1327 and P1330 are highly exposed to the solvent, whereas P1333 contact the FnIII-2 right before the β-strand H. (D) Structure of the CS in the complex of β4 (blue) with plectin (red). The view is in the same orientation as in panels A and B, and the CH2 was omitted for clarity. (E) Schematic representation of the FnIII-2 and the CS of β4 in the free (left) and plectin-bound (right) structures. The arrows illustrate the structural reorganisation of the CS induced by plectin binding.

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