Figure 3
From: The molecular architecture of dihydropyrindine receptor/L-type Ca2+ channel complex
Membrane topology determination, crystal structural docking and subunit assignments of DHPR complex.
(a) Membrane topology. The 3D EM maps of DHPR are coloured in cyan, the anti-α2 and anti-β antibodies are coloured in magenta and orange, respectively. The position of putative lipid bilayer is marked according to Figure 2b. As the α2 subunit is located on the extracellular side and the β subunit is located on the cytoplasmic side17,18, the membrane topology of DHPR can be determined from the subunit-specific antibody labelling as shown here, which is consistent with the direction and orientation of ion-conduction channel shown in Figure 2b. (b) Crystal structure docking and subunit assignments. Crystal structure of CavAb (PDB-ID:4MS2), a constructed bacterial Ca2+ channel and a homologue of the α1 subunit of DHPR and the cardiac DHPR β2a (a homologue of skeletal β subunit) complex with AID of the α1 subunit (PDB ID:1T0J) were fit into the pseudo-4-fold “trapezoid” and the “tetrahedroid” regions of the DHPR EM-map, respectively. Coloured ribbons represent the atomic models of the I–IV subunits of CavAb (red, yellow, cyan and blue) and the DHPR β subunit (green). Left: top view, viewed from the extracellular side, down the putative ion-conduction channel. Middle: side view (“diamond”), viewed parallel to the membrane plane, obtained by a rotation of 90° up-wards of the top view. Right: bottom view, viewed from the cytoplasmic side, obtained by a down-wards rotation of 180° of the top view. The putative locations of subunits α1, α2, β and δ are indicated.
