Structure of the plakin domain of plectin

Abstract

Plectin is a member of the plakin family of proteins that cross-links components of the cytoskeleton and link them to membrane-associated structures, such as hemidesmosomes. Plectin has a multi-domain structure. The N-terminal region contains a conserved domain terme the plakin domain that consists of an array of 9 Spectrin Repeats (SR1 to SR9) arranged in tandem and a Src-homology 3 (SH3) domain inserted in the central SR5. We have combined x-ray crystallography and SAXS to elucidate the structure of the plakin domain of plectin. Here, we present the crystal structure of several fragments of the central (SR3-SR6) and C-terminal region (SR7-SR9) of the plakin domain, that together cover the region SR3-SR9. Each SR consists on 3 helices (A,B y C) connected by short loops and packed in a helical bundle with a up-down-up topology. Adjacent SRs are linked by a continuos helix formed by the fusion of the helix-C of the N-terminal repeat and the helix-A of the C-terminal repeat. Yet there is no conservation in the relative orientation of adjacent SRs. The SH3 domain of plectin shows the canonical SH3 fold, but exhibits alterations in its putative Pro-rich binding-site suggesting that this domain does not bind to Pro-rich motifs. Moreover, the SH3 binding-site is occluded by intramolecular contacts with the SR4. Residues that participate in the SR4-SH3 interaction are conserved in other members of the plakin family. The structure of the plakin domain of plectin serves as a structural model for other plakins.