multi-color-localization-microscopy-single-membrane-proteins

Multi-color Localization Microscopy of Single Membrane Proteins in Organelles of Live Mammalian Cells

Knowledge about the localization of proteins in cellular subcompartments is crucial to understand their specific function. Here, we present a ...

While detailed information on the nanoscale-organization of proteins within intracellular membranes has emerged from electron microcopy, information on their spatiotemporal dynamics is scarce. By use of a photostable rhodamine attached specifically to Halo-tagged proteins in mitochondrial membranes, we were able to track and localize single protein complexes such as Tom20 and ATP synthase in suborganellar structures in live cells. Individual membrane proteins in the inner and outer membrane of mitochondria were imaged over long time periods with localization precisions below 15 nm. Projection of single molecule trajectories revealed diffusion-restricting microcompartments such as individual cristae in mitochondria. At the same time, protein-specific diffusion characteristics within different mitochondrial membranes could be extracted.

Nanoscale organization of mitochondrial microcompartments revealed by combining tracking and localization microscopy.

Mitochondria are the power plant of most non-green eukaryotic cells. An understanding of their function and regulation is only possible with the knowledge of the spatiotemporal dynamics of their proteins. Mitochondrial membrane proteins involved in diverse functions like protein import, cell respiration, metabolite transport, and mitochondrial morphology are mobile within membranes. Here, we provide a protocol for a superresolution fluorescence microscopy technique named tracking and localization microscopy (TALM) that allows for localization and diffusion analysis of single mitochondrial membrane proteins in situ in cell cultures. This noninvasive imaging technique is a useful tool to reveal the spatiotemporal organization of proteins in diverse mitochondrial membrane compartments in living cells. Proteins of interest are tagged with the HaloTag and specifically labeled with functionalized rhodamine dyes. The method profits from low abundance of proteins and therefore works better with substoichiometric labeling of HaloTag®-tagged proteins. In particular, the use of photostable bright rhodamine dyes enables the specific tagging and localization of single molecules with a calculated precision below 20 nm and the recording of single trajectories.

Single Molecule Tracking and Localization of Mitochondrial Protein Complexes in Live Cells.

Mitochondria are cellular organelles with multifaceted tasks and thus composed of different sub-compartments. The inner mitochondrial membrane especially has a complex nano-architecture with cristae protruding into the matrix. Related to their function, the localization of mitochondrial membrane proteins is more or less restricted to specific sub-compartments. In contrast, it can be assumed that membrane proteins per se diffuse unimpeded through continuous membranes. Fluorescence recovery after photobleaching is a versatile technology used in mobility analyses to determine the mobile fraction of proteins, but it cannot provide data on subpopulations or on confined diffusion behavior. Fluorescence correlation spectroscopy is used to analyze single molecule diffusion, but no trajectory maps are obtained. Single particle tracking (SPT) technologies in live cells, such as tracking and localization microscopy (TALM), do provide nanotopic localization and mobility maps of mitochondrial proteins in situ. Molecules can be localized with a precision of between 10 and 20 nm, and single trajectories can be recorded and analyzed; this is sufficient to reveal significant differences in the spatio-temporal behavior of diverse mitochondrial proteins. Here, we compare diffusion coefficients obtained by these different technologies and discuss trajectory maps of diverse mitochondrial membrane proteins obtained by SPT/TALM. We show that membrane proteins in the outer membrane generally display unhindered diffusion, while the mobility of inner membrane proteins is restricted by the inner membrane architecture, resulting in significantly lower diffusion coefficients. Moreover, tracking analysis could discern proteins in the inner boundary membrane from proteins preferentially diffusing in cristae membranes, two sub-compartments of the inner mitochondrial membrane. Thus, by evaluating trajectory maps it is possible to assign proteins to different sub-compartments of the same membrane.

Article	Year
Nanoscale organization of mitochondrial microcompartments revealed by combining tracking and localization microscopy. Nano letters\| PubMed ID: 22201267	2012
Single Molecule Tracking and Localization of Mitochondrial Protein Complexes in Live Cells. Methods in molecular biology (Clifton, N.J.)\| PubMed ID: 28276025	2017
Dynamic imaging of mitochondrial membrane proteins in specific sub-organelle membrane locations. Biophysical reviews\| PubMed ID: 28819924	2017

Timo Appelhans

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