Abstract
Calcium ion (Ca(2+)) serves as a second messenger for a variety of cell functions in trypanosomes. Several proteins in the plasma membrane, acidocalcisomes, endoplasmic reticulum, and mitochondria are involved in its homeostasis and in cell signaling roles. The plasma membrane has a Ca(2+) channel for its uptake and a plasma membrane-type Ca(2+)-ATPase (PMCA) for its efflux. A similar PMCA is also located in acidocalcisomes, acidic organelles that are the primary Ca(2+) store and that possess an inositol 1,4,5-trisphosphate receptor (IP₃R) for Ca(2+) efflux. Their mitochondria possess a mitochondrial calcium uniporter complex (MCUC) for Ca(2+) uptake and a Ca(2+)/H⁺ exchanger for Ca(2+) release. The endoplasmic reticulum has a sarcoplasmic-endoplasmic reticulum-type Ca(2+)-ATPase (SERCA) for Ca(2+) uptake but no Ca(2+) release mechanism has been identified. Additionally, the trypanosomatid genomes contain other membrane proteins that could potentially bind calcium and await further characterization.