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Updated: Jan 27, 2026

The CryoAPEX Method for Electron Microscopy Analysis of Membrane Protein Localization Within Ultrastructurally-Preserved Cells
Published on: February 27, 2020
CryoAPEX - an electron tomography tool for subcellular localization of membrane proteins
Ranjan Sengupta1, Michael J Poderycki1, Seema Mattoo2
1Department of Biological Sciences, Purdue University, 915 W. State St., LILY G-227, West Lafayette, IN 47907, USA.
Abstract:
We describe a method, termed cryoAPEX, which couples chemical fixation and high-pressure freezing of cells with peroxidase tagging (APEX) to allow precise localization of membrane proteins in the context of a well-preserved subcellular membrane architecture. Further, cryoAPEX is compatible with electron tomography. As an example, we apply cryoAPEX to obtain a high-resolution three-dimensional contextual map of the human FIC (filamentation induced by cAMP) protein, HYPE (also known as FICD). HYPE is a single-pass membrane protein that localizes to the endoplasmic reticulum (ER) lumen and regulates the unfolded protein response. Alternate cellular locations for HYPE have been suggested. CryoAPEX analysis shows that, under normal and/or resting conditions, HYPE localizes robustly within the subdomains of the ER and is not detected in the secretory pathway or other organelles. CryoAPEX is broadly applicable for assessing both lumenal and cytosol-facing membrane proteins.
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