What ATP binding does to the Ca <sup>2+</sup> pump and how nonproductive phosphoryl transfer is prevented in the absence of Ca <sup>2+</sup>
Yoshiki Kabashima, Haruo Ogawa, Rie Nakajima, Chikashi Toyoshima
Abstract
Significance During phosphoryl transfer from ATP in P-type ion translocating ATPases, very large-scale and complex structural changes take place, resulting in occlusion of ions to be translocated. In the present report, we describe a new crystal structure of a calcium pump in the absence of Ca 2+ but with a bound ATP analogue. We show that the ATP analogue is delivered to the phosphorylation site with a correct geometry despite the absence of Ca 2+ . Yet phosphoryl transfer from ATP never occurs in the absence of Ca 2+ , although phosphorylation by P i is possible as a backward reaction. We describe the structural changes that ATP binding alone elicits in the calcium pump and why Ca 2+ binding is absolutely necessary for phosphoryl transfer.