Peng Xia and Xuebiao Yao of the Hefei National Laboratory
for Physical Sciences at the Nanoscale and University of Science and Technology
of China, and their colleagues have managed to visualize protein interactions
at nanometer spatial resolution in live cells. The study is published in Molecular
Biology of the Cell (MBoC) and will also presented at the 2014 ASCB/IFCB
meeting in Philadelphia on December 8 at 1:30 pm in the ASCB Learning Center.
To move around cells have to keep reorganizing their
cytoskeleton, removing pieces from one end of a microtubule and add them to the
front, like a railroad with a limited supply of tracks. The EB protein family helps
regulate this process and can act as a scaffold for other proteins involved in
pushing the microtubule chain forward.
This new method uses photoactivatable complementary
fluorescent proteins (PACF) to observe and quantify protein-protein
interactions in live cells at the single molecule level. Yao and Xia introduced
two EB proteins into cells, one with half of a photoactivatable green
fluorescent protein (PAGFP), and one with the other half of PAGFP. These PAGFP
pieces will only fluoresce if the EB proteins are in a complex together and
photoactivated. A different wavelength of light can also be used to switch them
off. The researchers could assemble super-resolution images of protein
complexes by activating and then bleaching subsets of EB molecules.
The researchers opine that their technique has revealed a
critical role for a previously uncharacterized EB1 linker region in tracking
microtubule plus-ends in live cells. Precise localization of dynamic
microtubule plus-end hub protein EB1 dimers, and their distinct distributions
at the leading edge and cell body of migrating cells can be determined with the
help of this technique, which can be applied to the study of other protein
complexes in unprecedented detail.