The invention of green fluorescent protein (GFP) as a tool for observing cellular activity under fluorescence microscopy has accelerated life science research and rightfully earned a Nobel in chemistry.
GFP is still limited in higher resolution applications because it is dependent on visible light, the wavelength of which is much larger than what is being studied. A team of researchers led by a couple chemists at MIT have developed a protein tag that works much like GFP but at nanometer resolution of electron microscopy.
From the study abstract in Nature Biotechnology:
Here we report the development of ‘APEX’, a genetically encodable EM tag that is active in all cellular compartments and does not require light. APEX is a monomeric 28-kDa peroxidase that withstands strong EM fixation to give excellent ultrastructural preservation. We demonstrate the utility of APEX for high-resolution EM imaging of a variety of mammalian organelles and specific proteins using a simple and robust labeling procedure. We also fused APEX to the N or C terminus of the mitochondrial calcium uniporter (MCU), a recently identified channel whose topology is disputed3, 4. These fusions give EM contrast exclusively in the mitochondrial matrix, suggesting that both the N and C termini of MCU face the matrix. Because APEX staining is not dependent on light activation, APEX should make EM imaging of any cellular protein straightforward, regardless of the size or thickness of the specimen.
MIT press release: A new glow for electron microscopy
Study abstract in Nature Biotechnology: Engineered ascorbate peroxidase as a genetically encoded reporter for electron microscopy