Revisiting the Role of Toxoplasma gondii ERK7 in the Maintenance and Stability of the Apical Complex.

Nicolas Dos Santos Pacheco,Bohumil Maco,Nicolò Tosetti,Romuald Haase,Catherine Suarez,Bingjian Ren,Jon P Boyle,Dominique Soldati-Favre,Aarti Krishnan

doi:10.1128/mbio.02057-21

Abstract

ABSTRACTToxoplasma gondii extracellular signal-regulated kinase 7 (ERK7) is known to contribute to the integrity of the apical complex and to participate in the final step of conoid biogenesis. In the absence of ERK7, mature parasites lose their conoid complex and are unable to glide, invade, or egress from host cells. In contrast to a previous report, we show here that the depletion of ERK7 phenocopies the depletion of the apical cap protein AC9 or AC10. The absence of ERK7 leads to the loss of the apical polar ring (APR), the disorganization of the basket of subpellicular microtubules (SPMTs), and a severe impairment in microneme secretion. Ultrastructure expansion microscopy (U-ExM), coupled to N-hydroxysuccinimide ester (NHS-ester) staining on intracellular parasites, offers an unprecedented level of resolution and highlights the disorganization of the rhoptries as well as the dilated plasma membrane at the apical pole in the absence of ERK7. Comparative proteomics analysis of wild-type and ERK7-depleted parasites confirmed the disappearance of known apical complex proteins, including markers of the apical polar ring and a new apical cap named AC11. Concomitantly, the absence of ERK7 led to an accumulation of microneme proteins, resulting from the defect in the exocytosis of the organelles. AC9-depleted parasites were included as controls and exhibited an increase in inner membrane complex proteins, with two new proteins assigned to this compartment, namely, IMC33 and IMC34.

Highlights

Toxoplasma gondii extracellular signal-regulated kinase 7 (ERK7) is known to contribute to the integrity of the apical complex and to participate in the final step of conoid biogenesis
Both TgMAPKlike 1 and TgMAPK2 are involved in different steps of parasite replication [11, 12], while TgERK7 is involved in conoid biogenesis, hampering parasite invasion, egress, and dissemination [3]
We have revisited the role of ERK7 in the integrity of the apical complex of T. gondii in light of unmatching phenotypic consequences compared to Apical cap protein 9 (AC9) depletion [1, 3]

Summary

Introduction

Toxoplasma gondii extracellular signal-regulated kinase 7 (ERK7) is known to contribute to the integrity of the apical complex and to participate in the final step of conoid biogenesis. The absence of ERK7 leads to the loss of the apical polar ring (APR), the disorganization of the basket of subpellicular microtubules (SPMTs), and a severe impairment in microneme secretion. The conditional depletion of the apical cap structural protein AC9 or AC10 leads to a disorganization of SPMTs as well as the loss of the APR and conoid, resulting in a microneme secretion defect and a block in motility, invasion, and egress. AC9 was assigned a dual role in localizing ERK7 at the apical cap and in regulating its kinase activity and substrate specificity [2] Another protein, the conoidal ankyrin repeat-containing protein (CPH1), was reported to contribute to conoid integrity in extracellular parasites. The accumulation of microneme proteins reflected the severe defect in the exocytosis of these secretory organelles in the absence of ERK7

Methods

Results

Conclusion