Crystal structures of the calcium pump and sarcolipin in the Mg2+-bound E1 state.

P-type ATPases are ATP-powered ion pumps that establish ion concentration gradients across biological membranes, and are distinct from other ATPases in that the reaction cycle includes an autophosphorylation step. The best studied is Ca(2+)-ATPase from muscle sarcoplasmic reticulum (SERCA1a), a Ca(2+) pump that relaxes muscle cells after contraction, and crystal structures have been determined for most of the reaction intermediates. An important outstanding structure is that of the E1 intermediate, which has empty high-affinity Ca(2+)-binding sites ready to accept new cytosolic Ca(2+).

Trinitrophenyl derivatives bind differently from parent adenine nucleotides to Ca2+-ATPase in the absence of Ca2+.

Trinitrophenyl derivatives of adenine nucleotides are widely used for probing ATP-binding sites. Here we describe crystal structures of Ca(2+)-ATPase, a representative P-type ATPase, in the absence of Ca(2+) with bound ATP, trinitrophenyl-ATP, -ADP, and -AMP at better than 2.4-Å resolution, stabilized with thapsigargin, a potent inhibitor.

How processing of aspartylphosphate is coupled to lumenal gating of the ion pathway in the calcium pump.

Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum is the best-studied member of the P-type or E1/E2 type ion transporting ATPases. It has been crystallized in seven different states that cover nearly the entire reaction cycle. Here we describe the structure of this ATPase complexed with phosphate analogs BeF(3)(-) and AlF(4)(-) in the absence of Ca(2+), which correspond to the E2P ground state and E2 approximately P transition state, respectively.