Related Experiment Video
Updated: Aug 4, 2025
Preparing Lamellae from Vitreous Biological Samples Using a Dual-Beam Scanning Electron Microscope for Cryo-Electron Tomography
Published on: August 5, 2021
Cryo-tomography reveals rigid-body motion and organization of apicomplexan invasion machinery
Long Gui1, William J O'Shaughnessy2, Kai Cai1,3
1Department of Cell Biology, University of Texas, Southwestern Medical Center, Dallas, TX, USA.
Abstract:
The apical complex is a specialized collection of cytoskeletal and secretory machinery in apicomplexan parasites, which include the pathogens that cause malaria and toxoplasmosis. Its structure and mechanism of motion are poorly understood. We used cryo-FIB-milling and cryo-electron tomography to visualize the 3D-structure of the apical complex in its protruded and retracted states. Averages of conoid-fibers revealed their polarity and unusual nine-protofilament arrangement with associated proteins connecting and likely stabilizing the fibers. Neither the structure of the conoid-fibers nor the architecture of the spiral-shaped conoid complex change during protrusion or retraction. Thus, the conoid moves as a rigid body, and is not spring-like and compressible, as previously suggested. Instead, the apical-polar-rings (APR), previously considered rigid, dilate during conoid protrusion. We identified actin-like filaments connecting the conoid and APR during protrusion, suggesting a role during conoid movements. Furthermore, our data capture the parasites in the act of secretion during conoid protrusion.
Insights
The apical complex of malaria and toxoplasmosis parasites moves as a rigid body, not a spring. Apical-polar-rings dilate during protrusion, revealing new insights into parasite invasion mechanisms.
Area of Science:
- Cell biology
- Parasitology
- Structural biology
Background:
- Apicomplexan parasites, causing malaria and toxoplasmosis, possess a complex apical structure crucial for host cell invasion.
- The precise 3D-structure and motility mechanism of the apical complex remain poorly understood.
Purpose of the Study:
- To elucidate the 3D-structure of the apical complex in protruded and retracted states using advanced imaging techniques.
- To determine the structural dynamics of the conoid and associated components during parasite invasion.
Main Methods:
- Cryo-focused ion beam (cryo-FIB) milling combined with cryo-electron tomography (cryo-ET).
- 3D reconstruction and averaging of conoid fibers and the apical complex.
Main Results:
- The conoid moves as a rigid body; its structure is invariant during protrusion/retraction.
- Apical-polar-rings (APR) were found to dilate during conoid protrusion, contrary to previous assumptions.
- Actin-like filaments connecting the conoid and APR suggest a role in motility.
- Secretion events were observed concurrently with conoid protrusion.
Conclusions:
- The conoid's rigid-body motion, not compressibility, drives invasion.
- APR dilation and actin-like filaments are key components of the apical complex's motility mechanism.
- This study provides unprecedented structural detail of apicomplexan invasion machinery.
Related Concept Videos
01:07Electron Microscope Tomography and Single-particle Reconstruction
Electron Tomography
Electron tomography can be performed either in TEM or STEM (scanning transmission...
01:28Cryo-electron Microscopy