This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Before the parasite Toxoplasma gondii can invade a cell, it has to know it has reached the right place. New research from the Whitehead Institute reveals that the parasite doesn't simply recognize a ready-made doorway into the cell.
Instead, it helps create the conditions for its own entry. Researchers in the lab of Whitehead Institute member Sebastian Lourido have discovered that Toxoplasma reorganizes sugar-coated proteins on a host cell's surface, creating specialized membrane patches that depend on cholesterol and help trigger the parasite's invasion machinery. "The host cell, far from being a kind of passive, static entity in this process, is actually having its surface mixed around and remodeled by the parasite in order to achieve the right conditions for entry," said Lourido, also an associate professor of biology at MIT.
The study, led by first author Dylan Valleau, appears in The EMBO Journal on Sept. 25. Toxoplasma gondii is the single-celled parasite that causes toxoplasmosis. It belongs to a larger group of parasites called apicomplexans, which includes Plasmodium, the parasite responsible for malaria, and Cryptosporidium, which causes cryptosporidiosis.
These parasites must invade host cells to survive and reproduce. Toxoplasma completes the entire invasion process in less than a minute. Lourido's lab has long been interested in a fundamental mystery underlying that process: How does a parasite know when it has reached a host cell and should commit to entering?
A key step in that transition from contact to invasion is the discharge of contents from specialized organelles called rhoptries. At precisely the right moment, Toxoplasma releases their contents into the host cell. Among their cargo are proteins that manipulate the host cell and help establish receptors the parasite uses to enter—in effect, allowing Toxoplasma to make its own doorway.
Scientists had identified several components of the parasite machinery involved in rhoptry discharge, but what tells the parasite when to trigger that machinery remained unclear. The new study provides part of the answer. Rather than searching for additional parasite genes involved in invasion, the researchers approached the question from the other side.
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