Abstract
Background: Micronemal proteins of the thrombospondin-related anonymous protein (TRAP) family are believed to play essential roles during gliding motility and host cell invasion by apicomplexan parasites, and currently represent major vaccine candidates against Plasmodium falciparum, the causative agent of malaria. However, recent evidence suggests that they play multiple and different roles than previously assumed. Here, we analyse a null mutant for MIC2, the TRAP homolog in Toxoplasma gondii. Methods: We performed a careful analysis of parasite motility in a 3D-environment, attachment under shear stress conditions, host cell invasion and in vivo virulence. Results: We verified the role of MIC2 in efficient surface attachment, but were unable to identify any direct function of MIC2 in sustaining gliding motility or host cell invasion once initiated. Furthermore, we find that deletion of mic2 causes a slightly delayed infection in vivo, leading only to mild attenuation of virulence; like with wildtype parasites, inoculation with even low numbers of mic2 KO parasites causes lethal disease in mice. However, deletion of mic2 causes delayed host cell egress in vitro, possibly via disrupted signal transduction pathways. Conclusions: We confirm a critical role of MIC2 in parasite attachment to the surface, leading to reduced parasite motility and host cell invasion. However, MIC2 appears to not be critical for gliding motility or host cell invasion, since parasite speed during these processes is unaffected. Furthermore, deletion of MIC2 leads only to slight attenuation of the parasite.
Highlights
Apicomplexan parasites are obligate intracellular parasites that invade the host cell in an active process that involves the parasite’s own acto-myosin system acting in concert with parasitederived surface ligands (Meissner et al, 2013)
Gliding motility and host cell invasion by apicomplexan parasites have been thought to critically depend on members of the thrombospondin-related anonymous protein (TRAP) family, which are transmembrane proteins derived from the micronemes (Huynh & Carruthers, 2006; Sultan et al, 1997)
Aldolase was recently shown to be dispensable for gliding motility and invasion (Shen & Sibley, 2014b), but a new “connector” protein postulated to link the tail of MIC2 to actin has been described (Jacot et al, 2016)
Summary
Apicomplexan parasites are obligate intracellular parasites that invade the host cell in an active process that involves the parasite’s own acto-myosin system acting in concert with parasitederived surface ligands (Meissner et al, 2013). Depletion of MIC2 results in lower invasion rates, but has no influence on invasion speed we investigated the invasion process of mic KO parasites (Figure 5A) and found, as previously described (Huynh & Carruthers, 2006), that invasion is strongly inhibited, at 18 ± 3% relative to WT invasion levels In this assay the overall failure of invasion is measured, which could be due to defects in host cell attachment, junction formation or host cell penetration. Mic KO parasites invaded through a normal junction and penetrated the host cell at speeds similar to those of WT parasites (21.3 ± 11.7 s and 21.0 ± 6.9 s for WT and mic KO, respectively) (Videos S7 and Videos S8) These results lead us to conclude that the invasion deficiency observed for mic KO parasites is due to impaired attachment to the host cell, as suggested previously (Huynh & Carruthers, 2006). C) This localisation was supported by 3D diffuse tomographic reconstruction
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
