Fig. 3

Comparative structure models of OsCAX1a and OsMHX1 determined by homology modelling. a Models of OsCAX1a and OsMHX1 generated using the known structures of ScVCX1 and MjNCX, respectively. The proteins are viewed from within the membrane. OsCAX1a has 11 predicted transmembrane (TM) helices with the first non-conserved TM labelled as MR. TM helices that can be clearly sub-divided (kinked) are referred to as ‘a’ and ‘b’. M1 to M10 in both proteins are coloured equivalently, and the MR and acidic helix domains, and non-TM regions are shaded in grey. b Sequence alignment of the α-repeat sequences within helices M2/M3 and M7/M8. The signature sequence (GNXXE for CAX; GXSXPE/D for NCX) is boxed in red. c Comparison of the putative cation binding pocket of OsCAX1a and OsMHX1. Key residues of M2 and M7 that bind to a Ca²⁺ ion in ScVCX1 (relative to OsCAX1a) and in MjNCX (relative to OsMHX1) are indicated in parentheses while the equivalent residues in the same positions are shown. A Ca²⁺ ion is indicated in the OsCAX1a pocket. Substitution of a Glu residue (E54) with a Gln residue (Q102) in OsMHX1 may explain the lack of Ca²⁺ binding but Mg²⁺-binding residues are unknown