Speaker
Description
Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) transporters regulate calcium signaling by active calcium
ion reuptake to internal stores. Several of the structural transitions associated with transport have been characterized
by X-ray crystallography, but critical intermediates of the inward-outward switching are missing.
We combined time-resolved X-ray solution scattering (TR-XSS) experiments and molecular dynamics (MD)
simulations for real-time tracking of concerted SERCA reaction-cycle dynamics in the native membrane. The
TR-XSS pre-pulse model differed in the domain arrangement compared to Ca2E1 crystal structures. A 1.5
ms intermediate showed closure of the cytosolic domains typical of Ca2+- and ATP-bound E1 states. A subsequent
transi-ent state with a 13 ms rise-time showed a novel actuator (A) domain arrangement that exposes the
ADP-binding site after phosphorylation. Hence, the obtained TR-XSS models determine the relative timing
of so-far elusive domain rearrangements in a native environment.
