Fig. 6.
Diminished interactions between two major domains caused by Pi release. (A) In ADP-Pi–bound F-form actin, the interactions between two major domains, OD (magenta) and ID (cyan), are composed of the P1-loop (OD)/P2-loop (ID) interactions mediated by Pi and the sensor loop (OD)/P2-loop (ID) interactions mediated by the hydrogen bond (dotted cyan line) between Gly158 and Me-His73. (B) The ADP-bound F-form actin structure indicates that Pi release has two consequences, indicated as (1) loss of Pi and (2) hydrogen bond disruption. Both diminish the interdomain interactions, and thereby promote the F-to-G back transition (see SI Appendix, Fig. S10 for more details).