FIGURE 10.

Conserved 23-amino acid tandem membrane occupation and recognition nexus (MORN) repeat atomic structures and predicted junctophilin 2 (JPH2) β-strand architecture. A and B: Domain depiction and crystal structure of the NH₂-terminal deletion proteins Trypanosoma brucei TbMORN1(7–15) and Toxoplasma gondii TgMORN1(7-15) each forming tail-to-tail homodimers. Amino acid numbers and NH₂(N)/COOH (C) termini are indicated on top. The crystal structure is shown both from the side and 90° rotated as indicated. Major dimensions are indicated (double arrows). Each truncated protomer contains 9 MORN repeats of which the 3 COOH-terminal repeats additionally provide the antiparallel tail-to-tail interactions. The secondary structure consists exclusively of antiparallel β-strands and peripheral loops. TbMORN1(7–15) and TgMORN1(7–15) exhibit the same number of MORN repeats and structural configurations. Modified with permission from Sajko et al. (81). C: consensus MORN repeat sequence of TbMORN(7–15) revised according to its crystal structure. While repeats 7–15 exist in the crystal structure, the deleted repeats 1–6 are inferred. Blue color intensities indicate the conservation of sequence identity as indicated by the legend (%cutoff). TbMORN1 consists entirely of MORN repeats and β-hairpins, where the NH₂-terminal and COOH-terminal 6-residue β-strands are connected by a 5-residue loop. Finally, a 6-residue loop connects to the subsequent MORN repeat. The highly conserved GxG and additional motifs of the 23-residues consensus MORN repeat are indicated below. Modified with permission from Sajko et al. (81). D: conserved JPH2 YxGxW and GxG motifs of the 23-residues consensus MORN repeat sequence of JPH2. While the JPH2 sequence identity indicated by %cutoff (legend) is lower, the 6-residue tandem β-strands connected by a 5-residue loop are confirmed by similarity to the revised TbMORN1 consensus sequence.