Microneme protein 8 - A new essential invasion factor in Toxoplasma gondii

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 juction) with the host cell, through which the parasite invades. The functional characterisation of several micronemal proteins in Toxoplasma gondii suggests the occurence of a stepwise process. Here, we show that the micronemal protein MIC8 of T. gondii 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 cystolic 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 distinc invasion factor in this apicomplexan parasite.