(A) Helical regions of SR4, SR5, and SR6 are superimposed onto corresponding region of SR3. The color scheme is the same as in Figure 1B.
(B) Structure-based sequence alignments of SR3, SR4, SR5 and SR6 of desmoplakin. Secondary structure elements were assigned according to the program PROCHECK ⁵⁰. The α helices in the spectrin repeats are enclosed by green colored boxes and the a and d positions in the heptad patterns are shown above the sequences. The SH3 domain with N- and C-terminal linkers is inserted into the loop between helices B and C of SR5 at the position indicated by the red asterisk. Magenta boxes indicate β-strands in the SH3 domain. Blue and red underlined residues at the N-terminal linker region of the SH3 domain represent potential cleavage sites for trypsin and chymotrypsin, respectively.
(C) Comparison of hydrophobic interactions in SR3 and SR6. Trp194 in SR3 is a conserved aromatic residue position found in the hydrophobic core of most spectrin repeats, but is replaced by Asp556 in SR6, which faces toward the solvent region. In SR6, Phe600, located in the loop between helices B and C of SR6, participates in hydrophobic core interactions.

Residues mutated in ARVD/C are shown as sticks on ribbon representation of DP(175–630) in the same orientation as in the right figure of Figure 1b. Core residues, which contribute the structural integrity of DP(175–630) and surface residues are colored in cyan and red, respectively. A close up view of the SH3 domain and nearby regions is shown at the right.

(A) Desmoplakin primary structure. Desmoplakin consists of three major regions whose amino acid boundaries are indicated. A close up view of the plakin domain within DPNT is shown, with the colored regions representing the 4 spectrin repeats found in the crystal structure of DP(175–630).
(B) Overall structure of DP(175–630) shown as a ribbon representation and as an electrostatic surface (contoured at ±5 kT/e), shown in two orientations. The N and C termini and each spectrin repeat are labeled. Each spectrin repeat is colored as shown in panel (A).
(C) Packing of the two copies of DP(175–630) in the asymmetric unit, shown in green and purple.
(D) The two molecules in the asymmetric unit after superposition of their SR3 domains.

(A) Overall structure of the SH3 domain of desmoplakin. Beta-strands, RT loop, n-Src loop, and the N and the C termini are labeled.
(B) Comparison of canonical ligand-binding sites of the SH3 domains from desmoplakin and α-spectrin. The SH3 domain of α-spectrin and p41 peptide complex (PDB code 2JMA) (right) is shown in the same orientation as the SH3 domain of demoplakin (left). SR4 and the SH3 domain of desmoplakin are displayed in the same colors used in Figure 1; the SH3 domain of α-spectrin and its peptide ligand are colored yellow and red, respectively. Amino acid residues that form the canonical binding pocket of the SH3 domain in α-spectrin and those from equivalent positions in the SH3 domain of desmoplakin are labeled, and their side chains are shown as sticks; the Cα of glycine 509 is shown as a ball. Side chains of residues in SR4 interacting with the SH3 domain are also shown. The position of tryptophan 360 in SR4 overlaps that of proline in the p41 peptide ligand.

(A) Crystal structures of α-actinin (SRs1–4; PDB code 1HCI), α-spectrin (SR15-SR16-SR17; PDB code 1U4Q), erythroid β-spectrin (SR8-SR9; PDB code 1S35), plectin (SR1-SR2; PDB code 2ODU), and BPAG1e (SR3-SR4; PDB code 2IAK) were used for the comparison with the structure of DP(175–630). The N-terminal repeat of each protein was superimposed onto SR3 of desmoplakin (green). (B) The C-terminal repeat of BPAG1e, plectin, and β-spectrin are shown in apical view when their N-terminal repeats are superimposed into SR3 of DP(175–630). The color scheme is the identical to that in panel (A).