Direct visualization of vaults within intact cells by electron cryo-tomography

Area of Science:

• Cell biology
• Structural biology
• Biochemistry

Background:

• The vault complex is a large, evolutionarily conserved ribonucleoprotein complex found in eukaryotes.
• While its structure and composition are well-studied, the biological function of vaults remains largely unknown.
• Previous research focused on purified and recombinant vaults, with limited understanding of their native intracellular state.

Purpose of the Study:

• To investigate the morphology of intracellular vaults within intact human cells.
• To compare the structure of native vaults with previously characterized purified and recombinant vaults.
• To explore the intracellular associations and localization of vault complexes.

Main Methods:

• Electron cryo-tomography was employed to visualize vault complexes in primary human cells.
• Subtomogram averaging was used to analyze the internal structure of intracellular vaults.
• Ultrastructural analysis focused on vaults located in the cell periphery.

Main Results:

• Intracellular vaults exhibit similar overall size and shape to purified and recombinant vaults.
• Densities within the vault lumen were found to be randomly distributed, lacking ordered internal structure.
• Vaults at the cytoplasmic periphery were observed to associate with granule-like structures and actin filaments.

Conclusions:

• Intracellular vaults share morphological similarities with their purified counterparts.
• The random distribution of internal densities suggests a non-enzymatic or dynamic structural role.
• Peripheral associations with granules and actin provide crucial ultrastructural context for understanding native vault function.