CALCIUM LEVELS MODULATE POST- TRANSLATIONAL ARGINYLATION

MARCOS A. CARPIO; MARÍA BELÉN DECCA; MAURICIO R. GALIANO; MARTA E. HALLAK

Pinamar

Congreso; X Congreso Panamerican Association for Biochemistry and Molecular Biology, 41st Annual Meeting-Argentine Society for Biochemistry and Molecular Biology (SAIB), 20th Annual Meeting– Argentine Society for Neurochemistry; 2005

Argentine Society for Biochemistry and Molecular Biology - Argentine Society for Neurochemistry

Arginine can be posttranslationally incorporated by the enzyme arginyl-tRNA protein transferase into the NH2-terminus of soluble acceptor proteins. Among the arginylated proteins is calreticulina (CRT), a mayor intracellular calcium binding protein. Many cellular functions of CRT, such as chaperone and nuclear export activities are regulated by Ca+2 whose binding alters the conformation of CRT. Taking this into consideration, we studied if the posttranslational arginylation of CRT is also regulated by Ca+2. In vitro we found that the incorporation of 14C-arg is inhibited by Ca+2 whereas it is increased in the presence of the Ca+2 chelator EGTA. This is a specific effect on CRT since the arginylation of the other protein substrates was insensitive to calcium or EGTA. To address if arginylation of CRT is also modulated by Ca+2, we induced intracellular Ca+2 depletion in cultured cells by treatment with a combination of SERCA pump-inhibitor Thapsigargin and the membrane-permeant Ca+2 chelator Bapta-AM. We found that intracellular Ca+2 depletion dramatically increased the amount of arginylated CRT (100% respect to the cells cultured in the presence of Ca+2) as determined by immunocytochemistry assays. These results show that the posttranslational arginylation of CRT is regulated by Ca+2 levels, suggesting that a conformational change of CRT may be required for this modification to occur.