Intracellular calcium channels in protozoa

Abstract

Ca2+-signaling pathways and intracellular Ca2+ channels are present in protozoa. Ancient origin of inositol 1,4,5-trisphosphate receptors (IP3Rs) and other intracellular channels predates the divergence of animals and fungi as evidenced by their presence in the choanoflagellate Monosiga brevicollis, the closest known relative to metazoans. The first protozoan IP3R cloned, from the ciliate Paramecium, displays strong sequence similarity to the rat type 3 IP3R. This ciliate has a large number of IP3- and ryanodine(Ry)-like receptors in 6 subfamilies suggesting the evolutionary adaptation to local requirements for an expanding diversification of vesicle trafficking. IP3Rs have also been functionally characterized in trypanosomatids, where they are essential for growth, differentiation, and establishment of infection. The presence of the mitochondrial calcium uniporter (MCU) in a number of protozoa indicates that mitochondrial regulation of Ca2+ signaling is also an early appearance in evolution, and contributed to the discovery of the molecular nature of this channel in mammalian cells. There is only sequence evidence for the occurrence of two-pore channels (TPCs), transient receptor potential Ca2+ channels (TRPCs) and intracellular mechanosensitive Ca2+-channels in Paramecium and in parasitic protozoa.

Calcium Entry in Toxoplasma gondii and Its Enhancing Effect of Invasion-linked Traits

“…Specific searches in the T. gondii genome, as well as in other Apicomplexan genomes, have revealed no evidence for the existence of STIM or ORAI (27,28), in agreement with our results on the absence of SOCE in T. gondii. It is interesting to note, however, that evidence for the presence of STIM and ORAI orthologs has been reported in other unicellular protists, like the choanoflagellate Monosiga brevicollis, which belongs to the supergroup Ophisotkonta, which also includes animals and fungi (11,29).…”

“…Previous studies have shown that intracellular Ca 2ϩ stores are important for initiation of gliding motility (5), microneme secretion (6), conoid extrusion (7), active parasite invasion (8 -10), and egress (8) (reviewed in Ref. 11), but the role of extracellular Ca 2ϩ in these processes was not studied in detail or was considered minor.…”

Calcium signaling in trypanosomatid parasites

“…In T. brucei the IP 3 R localizes to acidocalcisomes rather than to the ER [4,5]. The acidocalcisome localization was first reported using the epitope-tagged protein [4,5] and recently confirmed using specific antibodies against TbIP 3 R [67].…”

“…The acidocalcisome localization was first reported using the epitope-tagged protein [4,5] and recently confirmed using specific antibodies against TbIP 3 R [67]. As indicated above (Section 4.1) evidence for ER localization in T. cruzi [54] is weak and contradicts proteomic analyses of acidocalcisomes and contractile vacuole complex of these parasites that provided evidence for the presence of the TcIP 3 R ortholog in these organelles [33].…”

“…They possess a limited number of plasma membrane Ca 2+ channels [1] and one putative voltage-gated Ca 2+ channel localizes to the flagellum [2], which is also where many Ca 2+ -binding proteins and enzymes involved in cell signaling also localize [3]. One particular intracellular Ca 2+ channel, the inositol 1,4,5-triphosphate receptor (IP 3 R) is not localized to the endoplasmic reticulum, as in most vertebrate cells, but to acidocalcisomes [4,5]. Acidocalcisomes are lysosome-related organelles, first described in trypanosomatids [6,7] and later found in a variety of cells, from bacteria to human cells [8], that are acidic and rich in phosphorus compounds (phosphate, pyrophosphate and polyphosphate) and cations.…”