SiMPull: Single Molecule Pull-Down


Cellular processes result from coordinated interactions between protein molecules. A detailed analysis of these interactions is central to understanding cell function and regulation. Traditionally, protein–protein interactions have been studied using a technique called ‘pull-down assay’, where, the target protein or 'bait' is captured from the cell or tissue extracts. When the bait protein is isolated, the proteins interacting with it, or the 'prey', are co-captured. These protein complexes are purified and subsequently analyzed using western blot or mass spectrometry. Using this analysis, however, it is often difficult to resolve complexity and functional role of the protein assemblies. Now, researchers at Taekjip Ha’s group have developed a novel technique, single molecule pull-down or SiMPull, for studying protein interactions at a single molecule resolution (Nature, 473, 484-488 (2011)). SiMPull combines conventional pull-down assay with single molecule imaging: protein complexes are pulled-down directly from fresh cultured cell or tissue extracts on to microscope slides and imaged under a single molecule fluorescence microscope. Once the complexes are immobilized on microscope slides, one can perform single molecule biochemistry to yield additional information about their composition and function. Additionally, the assay is very sensitive, “We can now use a single cell as opposed to 5000 cells for a regular western blot,” says Ha. “And this can be done in 20 minutes.”  Link to publication: