Antibodies against the Calcium-Binding Protein: Calsequestrin from Streptanthus tortuosus (Brassicaceae)

Plant microsomes contain a protein clearly related to a calcium-binding protein, calsequestrin, originally found in the sarcoplasmic reticulum of muscle cells, responsible for the rapid release and uptake of Ca²⁺ within the cells. The location and role of calsequestrin in plant cells is unknown. To generate monoclonal antibodies specific to plant calsequestrin, mice were immunized with a microsomal fraction from cultured cells of Streptanthus tortuosus (Brassicaceae). Two clones cross-reacted with one protein band with a molecular weight equal to that of calsequestrin (57 kilodaltons) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. This band is able to bind ⁴⁵Ca²⁺ and can be recognized by a polyclonal antibody against the canine cardiac muscle calsequestrin. Rabbit skeletal muscle calsequestrin cross-reacted with the plant monoclonal antibodies. The plant monoclonal antibodies generated here are specific to calsequestrin protein.