Identification of calcium-dependent phospholipid-binding proteins in higher plant cells

Calcium-dependent phospholipid-binding proteins of apparent M r 33 000 and 35 000 were isolated from suspension cultures of tomato cells. Two-dimensional gel electrophoresis showed the proteins to have isoelectric points of approx. 5.7 and 5.6, respectively. In the presence of calcium, both proteins bound to liposomes formed from a mixture of phosphatidylserine and phosphatidylcholine, but not to liposomes of phosphatidylcholine alone. Both proteins showed immunological similarities to previously characterized calcium-dependent phospholipid-binding proteins (annexins) from Torpedo marmorata and mammalian species. The protein of M r 33 000 cross-reacted with three separate antisera raised to the annexin Torpedo calelectrin, whereas that of M r 35 000 cross-reacted with antisera to the bovine annexins p68 and p32/34. We suggest that the two proteins may represent the first identification in higher plants of the annexin family of calcium-dependent phospholipid-binding proteins.