Sulfolipid is a potential candidate for annexin binding to the outer surface of chloroplast

Using a subcellular-specific proteomic approach, we have identified by prot ein microsequencing, a putative 35-kDa annexin from among the chloroplast e nvelope polypeptides, To confirm this identification, we demonstrate that ( a) a 35-kDa protein, identified as annexin by antibody cross-reactivity, co -purifies with Percoll-purified chloroplasts and their envelope membranes w hen extracted in the presence of Ca2+ and (b) the native spinach annexin pr otein binds to chloroplast-specific lipids in a Ca2+-dependent manner. The binding of the spinach annexin to these glycerolipids occurs at similar Ca2 + concentrations as those, which promote the interaction of annexins to pho spholipids in other membranes. Among chloroplast glycerolipids known to be accessible on the cytosolic face (outer leaflet) of the outer envelope memb rane, sulfolipid, and probably phosphatidylinositol, would be the sole cand idates for a putative Ca2+- dependent interaction of annexin with the chlor oplast surface. (C) 2000 Academic Press.