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. 2019 Feb 6;151(4):593–605. doi: 10.1085/jgp.201812268

Figure 3.

Figure 3.

State diagram of one RYR tetramer to illustrate calculation of binding energies ΔE. The states are identified by their energy Eo (for o = 0–3), expressed in parentheses in terms of the model parameters. As shown, the tetramer energy depends on its occupancy o and on simultaneous occupancy of adjacent protomers in adjacent tetramers. Eo may therefore adopt multiple values for the same occupancy. Among the many states available to a tetramer, the diagram illustrates those with four of five possible o values and up to two simultaneously occupied adjacent protomers. Arrows represent transitions.2 The diagonal gray arrows represent binding to (or unbinding from) a protomer that has the adjacent protomer occupied. In this example, the lower value of ΔE2 illustrates a case of Eq. 3 and the higher value illustrates Eq. 4 with starting occupancy o = 2 in both cases. Parameters ao and S have arbitrary values, which result in positive ΔE2; other possibilities are explored later.