The structure of the RIM C₂A domain is conserved from fly to man. (A) RIM protein layout for the human RIMS1 and the Drosophila homologue showing the position of its Rab3/Zinc-finger, PDZ, PxxP, C₂A and C₂B domains, known interaction partners are displayed above [the interaction with Munc13 (in parentheses) is observed only in mammals and not Drosophila]. Position of the CORD7 mutation site in the C₂A domain (red) is indicated. (B) Schematic representation of the Drosophila RIM C₂A domain structure. β-strands (β1-β8) are coloured in magenta and the 3₁₀-helix connecting β5 to β6 in yellow. The arginine doublet linked to CORD7 (R915, R916) is shown as sticks. The enlarged view of the dashed box (right) shows the superposition of the 3₁₀-helix region of Drosophila RIM C₂A (magenta) with rat RIM2 C₂A (green; PDB ID 2BWQ). (C) Protein alignments of wild-type RIM C₂A and C₂B domains (truncated for display purpose) from different species. HS = Homo sapiens; MM = Mus musculus; RN = Rattus norvegicus; DM = Drosophila melanogaster; CE = Caenorhabditis elegans. Alignments for C₂A and C₂B domains were calculated separately. Blue residues correspond to positions that are fully conserved between C₂A and C₂B domains in all displayed RIM homologues. Positions of the 3₁₀-helix (yellow), β-strands 5 and 6 (grey) of the Drosophila domain and the CORD7 mutation site in human (red) as part of an RR-motif are denoted. Note that the 3₁₀-helix with the arginine doublet is absent from RIM C₂B domains. GenBank/Uniprot entries: Q86UR5 (RIMS1-HS), Q99NE5 (RIMS1-MM), Q9EQZ7 (RIMS2-MM), Q80U57 (RIMS3-MM), P60191 (RIMS4-MM), AF199329 (RIM2-RN), V5M054 (RIM-DM), Q22366 (UNC-10-CE). (D) Electrostatic potential of accessible surfaces for the Drosophila RIM C₂A domain. Blue indicates positively charged regions, red negatively charged and white regions without charge. (E) Magnification of the domain bottom face in the wild-type, the CORD7 mutation and the RR > EE variants. See also Supplementary Table 1.