Abstract
Understanding membrane protein trafficking, assembly, and expression requires an approach that differentiates between those residing in intracellular organelles and those localized on the plasma membrane. Traditional fluorescence-based measurements lack the capability to distinguish membrane proteins residing in different organelles. Cutting edge methodologies transcend traditional methods by coupling pH-sensitive fluorophores with total internal reflection fluorescence microscopy (TIRFM). TIRF illumination excites the sample up to approximately 150 nm from the glass-sample interface, thus decreasing background, increasing the signal to noise ratio, and enhancing resolution. The excitation volume in TIRFM encompasses the plasma membrane and nearby organelles such as the peripheral ER. Superecliptic pHluorin (SEP) is a pH sensitive version of GFP. Genetically encoding SEP into the extracellular domain of a membrane protein of interest positions the fluorophore on the luminal side of the ER and in the extracellular region of the cell. SEP is fluorescent when the pH is greater than 6, but remains in an off state at lower pH values. Therefore, receptors tagged with SEP fluoresce when residing in the endoplasmic reticulum (ER) or upon insertion in the plasma membrane (PM) but not when confined to a trafficking vesicle or other organelles such as the Golgi. The extracellular pH can be adjusted to dictate the fluorescence of receptors on the plasma membrane. The difference in fluorescence between TIRF images at neutral and acidic extracellular pH for the same cell corresponds to a relative number of receptors on the plasma membrane. This allows a simultaneous measurement of intracellular and plasma membrane resident receptors. Single vesicle insertion events can also be measured when the extracellular pH is neutral, corresponding to a low pH trafficking vesicle fusing with the plasma membrane and transitioning into a fluorescent state. This versatile technique can be exploited to study localization, expression, and trafficking of membrane proteins.
Document Type
Article
Publication Date
3-16-2017
Digital Object Identifier (DOI)
https://doi.org/10.3791/55466
Funding Information
This work was supported in part by the National Institute on Drug Abuse T32 DA 016176, National Institute on Drug Abuse DA 038817, and National Institute on Drug Abuse DA 040047.
Related Content
The video component of this article can be found at https://www.jove.com/video/55466/.
Repository Citation
Fox-Loe, Ashley M.; Henderson, Brandon J.; and Richards, Christopher I., "Utilizing pHluorin-Tagged Receptors to Monitor Subcellular Localization and Trafficking" (2017). Chemistry Faculty Publications. 114.
https://uknowledge.uky.edu/chemistry_facpub/114
Materials List
Notes/Citation Information
Published in Journal of Visualized Experiments, issue 121, e55466, p. 1-7.
Copyright © 2017 Journal of Visualized Experiments
The copyright holder has granted the permission for posting the article here.