Structural analysis of crystalline Ca++ transport ATPase vesicles
In our efforts to study the three-dimensional structure and molecular organization of ion-motive ATPases by electron microscopy and image processing we have systematically investigated conditions which induce the formation of ordered arrays of these integral membrane proteins. Among them we have explored the effect(s) of vanadate and other multi-valent ions on ATPase crystal formation by starting from published procedures [e.g. 1,2]. Here we present some preliminary results concerned with the packing and molecular organization of vanadate-induced crystalline arrays of a Ca++ transport ATPase in tubular rabbit sarcoplasmic reticulum vesicles.The Ca++ activated ATPase from rabbit sarcoplasmic reticulum was purified as published. Induction of ordered tubular arrays of the protein with vanadate was basically achieved as described, except that the protein was slowly dialysed against a vanadate-containing buffer rather than directly adding the vanadate to the protein. Optimal yields of crystalline arrays were obtained after two days of dialysis at 4°C.