Genetically encoded FerriTag as a specific label for cryo-electron tomography.

Area of Science:

• Cell Biology
• Structural Biology
• Biophysics

Background:

• Cryo-electron tomography (cryoET) offers high-resolution 3D imaging of cellular components.
• Locating specific proteins within live cells using cryoET remains a significant technical hurdle.
• Existing labeling methods like fluorescent proteins or immunogold are often inadequate for small structures at molecular resolution in cryo-preserved samples.

Purpose of the Study:

• To develop an efficient and non-disruptive method for precisely localizing target proteins in live cells using cryoET.
• To overcome the limitations of conventional labeling techniques for high-resolution cellular imaging.

Main Methods:

• Utilized a rapamycin-inducible dimerization system employing FK506 binding protein (FKBP) and FKBP-rapamycin binding (FRB) domains.
• Fused FKBP to the target protein of interest and FRB to ferritin, a large, electron-dense complex.
• Induced FKBP-FRB binding with rapamycin, leading to ferritin accumulation at the target protein's location for cryoET visualization.

Main Results:

• Successfully demonstrated the rapamycin-induced localization of ferritin to target proteins in live cells.
• Achieved accurate spatial marking of target proteins, enabling their identification within complex cellular environments via cryoET.
• The ferritin tag provided strong contrast, facilitating detection at nanometer and sub-nanometer resolutions.

Conclusions:

• The FKBP-FRB-ferritin system provides a robust solution for targeting and visualizing specific proteins in live cells using cryoET.
• This method overcomes previous limitations, enabling high-resolution structural studies of protein localization and function in situ.
• Advances in cryoET and subtomogram averaging can be further leveraged with this innovative labeling strategy.