Directed evolution of APEX2 for electron microscopy and proximity labeling
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Updated: Apr 20, 2026

Mitochondria and Endoplasmic Reticulum Imaging by Correlative Light and Volume Electron Microscopy
Published on: July 20, 2019
Stephanie S Lam1, Jeffrey D Martell1, Kimberli J Kamer2
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
Abstract:
APEX is an engineered peroxidase that functions as an electron microscopy tag and a promiscuous labeling enzyme for live-cell proteomics. Because limited sensitivity precludes applications requiring low APEX expression, we used yeast-display evolution to improve its catalytic efficiency. APEX2 is far more active in cells, enabling the use of electron microscopy to resolve the submitochondrial localization of calcium uptake regulatory protein MICU1. APEX2 also permits superior enrichment of endogenous mitochondrial and endoplasmic reticulum membrane proteins.
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