Figure 8.

The SERCA transport cycle with structural states relevant to the present study. The preincubation and starting conditions used herein are indicated with corresponding structures of SERCA. Shown are the calcium-free E2 state (Protein Data Bank code 1IWO), an E1-like state promoted by calcium (Protein Data Bank code 1SU4), an E2-like state promoted by ATP (Protein Data Bank code 4H1W), and a catalytically active E1-ATP-Ca²⁺ state (Protein Data Bank code 1T5S). For condition iv with low calcium and high ATP concentrations, PLN inhibition appears to follow the on-pathway E2 to E1 transition; however, the structural state of SERCA under these conditions is unknown.