Protein Tags for Enhanced in Vivo Imaging

Technology #15128

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Professor Alice Ting
Department of Chemistry, MIT
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Jeffrey Martell
Department of Chemistry, MIT
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Tod Woolf
MIT Technology Licensing Officer
Patent Protection

Cytosolically-active peroxidases as reporters for microscopy

US Patent Issued
Engineered ascorbate peroxidase as a genetically encoded reporter for electron microscopy
Nature Biotechnology, 2012 Nov;30(11):1143-8


This method enables high-resolution cell imaging, using either light or electron microscopy, and is especially useful for probing protein-protein interactions.

Problem Addressed

Determining protein localization in live cells while maintaining sample integrity is difficult. Traditional techniques involve antibody staining of target proteins, but the permeablization treatments required for antibody access compromise cellular ultrastructure. Alternatives are limited by an inconvenient requirement for light and oxygen gas (which restricts their use to thin samples), or lack of activity in most cellular compartments.


Professor Alice Ting and colleagues have developed a tool that involves genetically fusing an engineered ascorbate peroxidase (APEX), to a protein of interest to catalyze the production of an electron-dense precipitate that is easily visualized with either light or electron microscopy. This reaction occurs quickly and locally, thereby attaining very high spatial resolution. The tag is non-toxic, is functional in all cellular compartments, and does not sterically hinder native proteins. Furthermore, it can be fused to fluorescent proteins, allowing for images from electron microscopy to be correlated with those from light microscopy. APEX2, an improved version of this enzyme, will be available shortly.


  • High spatiotemporal resolution 
  • Can be used to combine multiple imaging modalities
  • Genetic tag is small, sterically compatible with most proteins, and can be expressed in all cellular compartments
  • Can be used on samples of any thickness (reaction is not light-dependent) 
  • Straightforward method