Rearrangement of boundary, stand-by, and fluid lipids during the formation of two-dimensional crystals of Ca2+-ATPase

Abstract

Ca2+-transport ATPase of sarcoplasmic reticulum of rabbit skeletal and carp abdominal muscle is essential for the removal of large amounts of Ca2+ ions during the relaxation of the muscle. As in the case of other lipid–protein systems, fluid lipid and motionally restricted boundary lipid sites lead to multicomponent spin label EPR spectra. Having subtracted the dominating fluid component a two-component lineshape is recovered as a subtraction endpoint, suggesting the presence of a third, motionally less restricted stand-by lipid shell as fraction of boundary lipids. On adding 5mM decavanadate the phosphate binding site is blocked and the protein dimers form a two dimensional array, at least in the case of the sarcoplasmic reticulum of rabbit. During two-dimensional crystal formation of rabbit Ca2+-ATPase an increase of lipids was found in boundary and stand-by shells. No such change was observed in the case of the sarcoplasmic reticulum of carp abdominal muscle.