Figure 6.

Model of α_1S–β_1a interactions in the assembly of the DHP receptor complex in the skeletal muscle triad. β_1a without the α_1S subunit is localized in the cytoplasm. On coexpression β_1a and α_1S form a complex in the endoplasmic reticulum that is then incorporated into the junctional T-tubules (TT). Deletion of the β interaction domain in the I–II cytoplasmic loop blocks β_1a association and export of the α_1S mutant (α_1S-Δ) from the endoplasmic reticulum. A point mutation (α_1S-Y366S) in the high affinity β_1a binding site of α_1S (symbolized by the rectangular nipple) inhibits α_1S/β_1a complex formation but not the functional incorporation of the mutated α_1S-Y366S into the T-tubules. Dynamic interactions between free cytoplasmic β_1a and a low affinity interaction site (symbolized by the triangular notch) may modulate Ca²⁺ currents of α_1S-Y366S and may be involved in the translocation of α_1S-Y366S into the T-tubules.