Fig. 6.

Allosteric model of PLN interaction with SERCA. PLN monomer interconverts between the bent form (T state) and the less stable (more dynamically disordered) extended form (R state). The T state inhibits SERCA because of its interaction in the transmembrane domain. Only in the R state, in which the cytoplasmic domains interact, is SERCA-bound PLN capable of reversing SERCA inhibition, because of PLN phosphorylation or mutation. SERCA has a greater affinity for the R form and thus shifts the equilibrium toward this regulatory intermediate.