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Updated: Jan 25, 2026
Determination of Chemical Inhibitor Efficiency against Intracellular Toxoplasma Gondii Growth Using a Luciferase-Based Growth Assay
Published on: April 29, 2020
Microneme protein 8--a new essential invasion factor in Toxoplasma gondii
Henning Kessler1, Angelika Herm-Götz, Stephan Hegge
1Hygieneinstitute, Department of Parasitology, University Hospital Heidelberg, Im Neuenheimer Feld 324, D-69120 Heidelberg, Germany.
Abstract:
Apicomplexan parasites rely on sequential secretion of specialised secretory organelles for the invasion of the host cell. First, micronemes release their content upon contact with the host cell. Second, rhoptries are discharged, leading to the formation of a tight interaction (moving junction) with the host cell, through which the parasite invades. The functional characterisation of several micronemal proteins in Toxoplasma gondii suggests the occurrence of a stepwise process. Here, we show that the micronemal protein MIC8 of T. gondii is essential for the parasite to invade the host cell. When MIC8 is not present, a block in invasion is caused by the incapability of the parasite to form a moving junction with the host cell. We furthermore demonstrate that the cytosolic domain is crucial for the function of MIC8 and can not be functionally complemented by any other micronemal protein characterised so far, suggesting that MIC8 represents a novel, functionally distinct invasion factor in this apicomplexan parasite.
Insights
The apicomplexan parasite Toxoplasma gondii requires the MIC8 protein for host cell invasion. Without MIC8, parasites cannot form the moving junction necessary for entry, highlighting MIC8 as a distinct invasion factor.
Area of Science:
- Parasitology
- Cell Biology
- Molecular Biology
Background:
- Apicomplexan parasites invade host cells through a sequential process involving specialized secretory organelles.
- Micronemes and rhoptries are key organelles, with microneme secretion preceding rhoptry discharge for host cell interaction and invasion.
- Previous studies on Toxoplasma gondii micronemal proteins suggest a stepwise invasion mechanism.
Purpose of the Study:
- To investigate the essential role of the micronemal protein MIC8 in the host cell invasion process of Toxoplasma gondii.
- To determine the specific function of MIC8 during parasite invasion and its contribution to the formation of the moving junction.
Main Methods:
- Functional characterization of the micronemal protein MIC8 in Toxoplasma gondii.
- Analysis of parasite invasion capabilities in the absence of MIC8.
- Investigation of the role of the cytosolic domain of MIC8 in parasite function.
Main Results:
- The micronemal protein MIC8 is essential for Toxoplasma gondii host cell invasion.
- Absence of MIC8 prevents the formation of the moving junction, blocking parasite entry.
- The cytosolic domain of MIC8 is critical for its function and cannot be substituted by other known micronemal proteins.
Conclusions:
- MIC8 is a novel and functionally distinct invasion factor in apicomplexan parasites.
- The specific function of MIC8 in moving junction formation is crucial for parasite invasion.
- MIC8 represents a unique target for therapeutic strategies against apicomplexan infections.
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