Control of host invasion by protein complexes conserved across apicomplexan parasites - 7. Project summary/abstract how apicomplexan parasites recognize host cells to invade them remains a mystery

The National Institute of Allergy and Infectious Diseases awarded Whitehead Institute for Biomedical Research $899,850 on February 20, 2026, under the Allergy and Infectious Diseases Research program (CFDA 93.855) to investigate how apicomplexan parasites recognize and invade host cells.

The funded research examines the molecular mechanisms by which parasites such as Toxoplasma and Plasmodium trigger rhoptry discharge—the secretion of proteins from specialized organelles upon contact with host cells—as a gateway to intracellular invasion. The project tests the hypothesis that two conserved microneme protein complexes, the clamp and crmp complexes, recognize host-cell N-glycans to mediate rhoptry discharge. Aim 1 determines the glycan specificity of these complexes using glycan arrays. Aim 2 uses high-speed live-cell imaging to characterize how host N-glycosylation alters invasion stages and isolates defects in rhoptry discharge. Aim 3 applies phosphoproteomics and proximity-labeling to characterize signaling events triggered by host-cell recognition. Work is performed in Cambridge, Massachusetts, with a period of performance from February 20, 2026, through January 31, 2031. The award is structured as a Project Grant, the standard NIH research funding mechanism for investigator-led basic and translational science.

Since these parasites only replicate intracellularly, invading host cells is essential to their survival. Invasion relies on the coordinated secretion of proteins from two distinct types of organelles: micronemes and rhoptries. Rhoptries are exclusively discharged upon host-cell contact; however, the molecular events that trigger this process remain completely unknown. Understanding the factors required for rhoptry discharge can help US uncover the basis of host-cell recognition. Two conserved microneme complexes-the clamp and crmp complexes-have recently been shown by the lourido and lebrun labs to be required for rhoptry discharge, making them likely mediators of host-cell recognition. Our preliminary studies have identified n-glycosylation pathways as key host requirements for rhoptry discharge. Loss of host n-glycosylation significantly reduced rhoptry discharge, while buffering any additional effect from knocking down the clamp or crmp complexes. Based on these observations, we hypothesize that the clamp and crmp complexes recognize host cells through n-glycans to mediate rhoptry discharge. This proposal brings together the two teams that discovered these critical complexes to examine how they recognize host n-glycosylation and mediate rhoptry discharge. Aim 1 will determine the glycan specificity of the clamp and crmp complexes through traditional or liquid glycan arrays. Aim 2 will characterize how n-glycosylation alters the various stages of invasion using high-speed live-cell imaging to dissect the multi-stage invasion process and pinpoint defects to rhoptry discharge. Aim 3 will characterize the signaling events triggered by host-cell recognition through phosphoproteomics and proximity-labeling. Taken together the proposed experiments will uncover how apicomplexans respond to host contact to discharge rhoptries and initiate invasion. Beyond its fundamental importance, this information can be used to design inhibitors of host cell entry that would block parasite infection.