DISTINCT STRUCTURAL IDENTITIES OF CATALYTIC AND CA-2+ BINDING DOMAINS IN THE SARCOPLASMIC-RETICULUM ATPASE

Electron microscopic visualization and diffraction patterns yield a profile for the 110-kD SR ATPase, which includes a globular cytosolic region connected through a stalk to a membrane-bound region. Chemical derivatization and mutagenesis demonstrate that the catalytic domain is located within the cytosolic region and the Ca2+ binding domain within the membrane-bound region. The catalytic domain of the Ca2+-ATPase and of the Na+/K+-ATPase can be interchanged by chimeric recombination without affecting the Ca2+ binding domain. Considerable detail of the ATPase folding pattern and functional structures is obtained by spectroscopic experiments and molecular modelling. The long-range functional linkage between the catalytic and Ca2+ binding domains appears to involve protein structural changes, most likely consisting of segmental reorientation with minimal alteration of secondary structure.