New crystal structures of PII-type ATPases: excitement continues.

P-type ATPases are ATP-powered ion pumps, classified into five subfamilies (PI-PV). Of these, PII-type ATPases, including Ca2+-ATPase, Na+,K+-ATPase and gastric H+,K+-ATPase, among others, have been the most intensively studied. Best understood structurally and biochemically is Ca2+-ATPase from sarcoplasmic reticulum of fast twitch skeletal muscle (sarco(endo)plasmic reticulum Ca2+-ATPase 1a, SERCA1a). Since publication of the first crystal structure in 2000, it has continuously been a source of excitement, as crystal structures for new reaction intermediates always show large structural changes. Crystal structures now exist for most of the reaction intermediates, almost covering the entire reaction cycle. This year the crystal structure of a missing link, the E1·Mg2+ state, finally appeared, bringing another surprise: bound sarcolipin (SLN). The current status of two other important PII-type ATPases, Na+,K+-ATPase and H+,K+-ATPase, is also briefly described.