Abstract
The binding of plectin to the beta4 subunit of the alpha6beta4 integrin is a critical step in the formation of hemidesmosomes. An important interaction between these two proteins occurs between the actin-binding domain (ABD) of plectin and the first pair of fibronectin type III (FNIII) domains and a small part of the connecting segment of beta4. Previously, a few amino acids, critical for this interaction, were identified in both plectin and beta4 and mapped on the crystal structures of the ABD of plectin and the first pair of FNIII domains of beta4. In the present study, we used this biochemical information and protein-protein docking calculations to construct a model of the binary complex between these two protein domains. The top scoring computational model predicts that the calponin-homology 1 (CH1) domain of the ABD associates with the first and the second FNIII domains of beta4. Our mutational analysis of the residues at the proposed interface of both the FNIII and the CH1 domains is in agreement with the suggested interaction model. Computational simulations to predict protein motions suggest that the exact model of FNIII and plectin CH1 interaction might well differ in detail from the suggested model due to the conformational plasticity of the FNIII domains, which might lead to a closely related but different mode of interaction with the plectin-ABD. Furthermore, we show that Ser-1325 in the connecting segment of beta4 appears to be essential for the recruitment of plectin into hemidesmosomes in vivo. This is consistent with the proposed model and previously published mutational data. In conclusion, our data support a model in which the CH1 domain of the plectin-ABD associates with the groove between the two FNIII domains of beta4.
Highlights
Several kinds of skin blistering diseases are known to be due to defects in the adhesion of basal cells of the epidermis to the underlying basement membrane
The region of 4 predicted to interact with the plectin-actin-binding domain (ABD) extends over an interdomain region that includes the C-CЈ and E-F loops in the first fibronectin type III (FNIII) and the lower part of the ABE sheet and the B-C loop of the second FNIII domain
The calponin-homology 1 (CH1) domain, but not the CH2 domain, of the plectin-ABD was predicted to be involved in direct binding to this interdomain region of 4
Summary
Several kinds of skin blistering diseases are known to be due to defects in the adhesion of basal cells of the epidermis to the underlying basement membrane. Missense mutations in the gene encoding 4 have been described in patients with a non-lethal form of epidermolysis bullosa (EB) [3, 4] These mutations (R1225H and R1281W) have been shown to result in a failure of 4 to recruit the intermediate filament linker protein plectin into the epithelial adhesive superstructures called hemidesmosomes [5]. The loss or a reduced expression of plectin results in a skin blistering disorder called epidermolysis bullosa simplex associated with muscular dystrophy. This further confirms the importance of the interaction of ␣64 with plectin in maintaining epithelial integrity (6 –9). Plectin-4 Docking Model mains of 4 have been determined [22,23,24] but not the structure of the complex of the two proteins
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