The Vacuolar Zinc Transporter TgZnT Protects Toxoplasma gondii from Zinc Toxicity

摘要

Zinc (Znsup2+/sup) is the most abundant biological metal ion aside from iron and is an essential element in numerous biological systems, acting as a cofactor for a large number of enzymes and regulatory proteins. Znsup2+/sup must be tightly regulated, as both the deficiency and overabundance of intracellular free Znsup2+/sup are harmful to cells. Znsup2+/sup transporters (ZnTs) play important functions in cells by reducing intracellular Znsup2+/sup levels by transporting the ion out of the cytoplasm. We characterized a Toxoplasma gondii gene (TgGT1_251630, TgZnT), which is annotated as the only ZnT family Znsup2+/sup transporter in T. gondii . TgZnT localizes to novel vesicles that fuse with the plant-like vacuole (PLV), an endosome-like organelle. Mutant parasites lacking TgZnT exhibit reduced viability in in vitro assays. This phenotype was exacerbated by increasing zinc concentrations in the extracellular media and was rescued by media with reduced zinc. Heterologous expression of TgZnT in a Znsup2+/sup-sensitive Saccharomyces cerevisiae yeast strain partially restored growth in media with higher Znsup2+/sup concentrations. These results suggest that TgZnT transports Znsup2+/sup into the PLV and plays an important role in the Znsup2+/sup tolerance of T. gondii extracellular tachyzoites. IMPORTANCE Toxoplasma gondii is an intracellular pathogen of human and animals. T. gondii pathogenesis is associated with its lytic cycle, which involves invasion, replication, egress out of the host cell, and invasion of a new one. T. gondii must be able to tolerate abrupt changes in the composition of the surrounding milieu as it progresses through its lytic cycle. We report the characterization of a Znsup2+/sup transporter of T. gondii (TgZnT) that is important for parasite growth. TgZnT restored Znsup2+/sup tolerance in yeast mutants that were unable to grow in media with high concentrations of Znsup2+/sup. We propose that TgZnT plays a role in Znsup2+/sup homeostasis during the T. gondii lytic cycle.