Journal: Nat Commun / Year: 2023 Title: Origin and arrangement of actin filaments for gliding motility in apicomplexan parasites revealed by cryo-electron tomography. Authors: Matthew Martinez / Shrawan Kumar Mageswaran / Amandine Guérin / William David Chen / Cameron Parker Thompson / Sabine Chavin / Dominique Soldati-Favre / Boris Striepen / Yi-Wei Chang / Abstract: The phylum Apicomplexa comprises important eukaryotic parasites that invade host tissues and cells using a unique mechanism of gliding motility. Gliding is powered by actomyosin motors that ...The phylum Apicomplexa comprises important eukaryotic parasites that invade host tissues and cells using a unique mechanism of gliding motility. Gliding is powered by actomyosin motors that translocate host-attached surface adhesins along the parasite cell body. Actin filaments (F-actin) generated by Formin1 play a central role in this critical parasitic activity. However, their subcellular origin, path and ultrastructural arrangement are poorly understood. Here we used cryo-electron tomography to image motile Cryptosporidium parvum sporozoites and reveal the cellular architecture of F-actin at nanometer-scale resolution. We demonstrate that F-actin nucleates at the apically positioned preconoidal rings and is channeled into the pellicular space between the parasite plasma membrane and the inner membrane complex in a conoid extrusion-dependent manner. Within the pellicular space, filaments on the inner membrane complex surface appear to guide the apico-basal flux of F-actin. F-actin concordantly accumulates at the basal end of the parasite. Finally, analyzing a Formin1-depleted Toxoplasma gondii mutant pinpoints the upper preconoidal ring as the conserved nucleation hub for F-actin in Cryptosporidium and Toxoplasma. Together, we provide an ultrastructural model for the life cycle of F-actin for apicomplexan gliding motility.
Organelle or cellular component: IMC surface filaments, top view
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Supramolecule #1: IMC surface filaments, top view
Supramolecule
Name: IMC surface filaments, top view / type: organelle_or_cellular_component / ID: 1 / Parent: 0 Details: In situ structure of the IMC surface filaments, top view, from Cryptosporidium parvum sporozoites
Source (natural)
Organism: Cryptosporidium parvum Iowa (eukaryote)
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Experimental details
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Structure determination
Method
cryo EM
Processing
subtomogram averaging
Aggregation state
particle
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Sample preparation
Buffer
pH: 7.4
Grid
Model: Quantifoil R2/2 / Material: COPPER / Mesh: 200 / Support film - Material: CARBON / Support film - topology: HOLEY / Pretreatment - Type: GLOW DISCHARGE
Vitrification
Cryogen name: ETHANE-PROPANE / Chamber humidity: 99 % / Chamber temperature: 310 K / Instrument: LEICA EM GP Details: Isolated sporozoites were resuspended in media, and 4 uL was applied to the carbon side of the grid and front blotted for 4s.
Details
Sample was averaged from within frozen-hydrated Cryptosporidium parvum sporozoites
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Electron microscopy
Microscope
FEI TITAN KRIOS
Specialist optics
Phase plate: VOLTA PHASE PLATE / Energy filter - Name: GIF Bioquantum / Energy filter - Slit width: 20 eV
Image recording
Film or detector model: GATAN K3 (6k x 4k) / Average exposure time: 0.4 sec. / Average electron dose: 2.3 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Applied symmetry - Point group: C1 (asymmetric) / Resolution.type: BY AUTHOR / Resolution: 38.5 Å / Resolution method: FSC 0.5 CUT-OFF / Software - Name: Dynamo (ver. 1.1.509) / Number subtomograms used: 5421
Extraction
Number tomograms: 24 / Number images used: 6709 / Method: Filaments traced / Software - Name: Dynamo (ver. 1.1.509) Details: Traced filaments in IMOD. Imported coordinates into Dynamo, where points were placed along each filament trace.
Final angle assignment
Type: NOT APPLICABLE / Software - Name: Dynamo (ver. 1.1.509)
FSC plot (resolution estimation)
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