Ca²⁺ Content and Expression of an Acidocalcisomal Calcium Pump Are Elevated in Intracellular Forms ofTrypanosoma cruzi

Abstract

The survival of a eukaryotic protozoan as an obligate parasite in the interior of a eukaryotic host cell implies its adaptation to an environment with a very different ionic composition from that of its extracellular habitat.

A Functional Aquaporin Co-Localizes with the Vacuolar Proton Pyrophosphatase to Acidocalcisomes and the Contractile Vacuole Complex of Trypanosoma cruzi

“…However, some acidocalcisomes were labeled with antibodies against TcAQP but not with antibodies against TcPPase, and vice versa. Similar heterogeneity in labeling of acidocalcisomes with antibodies against a V-H ϩ -ATPase and a Ca 2ϩ -ATPase has been reported before (35) and could suggest the existence of different populations of acidocalcisomes. However, we cannot rule out the possibility that some aquaporin could be labeling another unidentified organelle.…”

TcSCA Complements Yeast Mutants Defective in Ca2+ Pumps and Encodes a Ca2+-ATPase That Localizes to the Endoplasmic Reticulum of Trypanosoma cruzi

“…Invasion of cells by T. cruzi is dependent upon an elevation in the concentration of cytosolic free calcium in the invading trypomastigote (1,2). Unlike mammalian cells, T. cruzi possesses most of its intracellular Ca 2ϩ in an acidic compartment named the acidocalcisome (3)(4)(5)(6)(7)(8). The molecular and biochemical characterization of this organelle has provided evidence that it has an orthovanadate-sensitive plasma membrane-type Ca 2ϩ ATPase for Ca 2ϩ uptake (3,(5)(6)(7).…”

“…Expression of genes identified as encoding Ca 2ϩ -ATPases and localization of the corresponding proteins is necessary, as the plasma membrane-type Ca 2ϩ ATPase/SERCA paradigm does not necessarily apply in nonanimal cells; a SERCA-type gene in tomato is expressed in different parts of the cell (16). Also, a Tca1 gene has been identified in T. cruzi (6), which encodes a protein with homology to mammalian plasma membrane Ca 2ϩ -ATPases but with characteristics that place it in a novel category of Ca 2ϩ -ATPases along with the vacuolar Ca 2ϩ -ATPases described in Saccharomyces cerevisiae (17), Dictyostelium discoideum (18), Entamoeba histolytica (19), and Toxoplasma gondii (20). The gene is expressed at a high level in the amastigote stage and is localized to acidocalcisomes and the plasma membrane of the parasite (6).…”

“…Unlike mammalian cells, T. cruzi possesses most of its intracellular Ca 2ϩ in an acidic compartment named the acidocalcisome (3)(4)(5)(6)(7)(8). The molecular and biochemical characterization of this organelle has provided evidence that it has an orthovanadate-sensitive plasma membrane-type Ca 2ϩ ATPase for Ca 2ϩ uptake (3,(5)(6)(7). Evidence for non-mitochondrial and endoplasmic reticulumlocated Ca 2ϩ uptake has been more elusive and based on the presence of a low capacity and high affinity orthovanadatesensitive Ca 2ϩ uptake in permeabilized cells and the ability of these cells to buffer [Ca 2ϩ ] in the range 0.05-0.1 M (9), features in common with the sarcoplasmic/endoplasmic reticulum Ca 2ϩ -ATPases (SERCA) 1 of animal cells (10).…”

“…(6). The Alexafluor 564-conjugated goat anti-rabbit antibody was from Molecular Probes (Eugene, OR).…”