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

Using a subcellular-specific proteomic approach, we have identified by protein microsequencing, a putative 35-kDa annexin from among the chloroplast envelope 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 when extracted in the presence of Ca(2+) and (b) the native spinach annexin protein binds to chloroplast-specific lipids in a Ca(2+)-dependent manner. The binding of the spinach annexin to these glycerolipids occurs at similar Ca(2+) concentrations as those, which promote the interaction of annexins to phospholipids in other membranes. Among chloroplast glycerolipids known to be accessible on the cytosolic face (outer leaflet) of the outer envelope membrane, sulfolipid, and probably phosphatidylinositol, would be the sole candidates for a putative Ca(2+)-dependent interaction of annexin with the chloroplast surface.