| Popis: |
Under physiological conditions, most Ca(2+)-ATPase (SERCA) molecules bind ATP before binding the Ca(2+) transported. SERCA has a high affinity for ATP even in the absence of Ca(2+), and ATP accelerates Ca(2+) binding at pH values lower than 7, where SERCA is in the E2 state with low-affinity Ca(2+)-binding sites. Here we describe the crystal structure of SERCA2a, the isoform predominant in cardiac muscle, in the E2·ATP state at 3.0-Å resolution. In the crystal structure, the arrangement of the cytoplasmic domains is distinctly different from that in canonical E2. The A-domain now takes an E1 position, and the N-domain occupies exactly the same position as that in the E1·ATP·2Ca(2+) state relative to the P-domain. As a result, ATP is properly delivered to the phosphorylation site. Yet phosphoryl transfer never takes place without the filling of the two transmembrane Ca(2+)-binding sites. The present crystal structure explains what ATP binding itself does to SERCA and how nonproductive phosphorylation is prevented in E2. |
