Labeling of Proteins in vitro (S9106)


  1. Dissolve the vial of SNAP-Cell Block (100 nmol) in 50 μl of fresh DMSO to yield a labeling stock solution of 2 mM SNAP-Cell Block. Mix by vortexing for 10 minutes until all the SNAP-tag substrate is dissolved. Dilute this 2 mM stock solution 1:4 in fresh DMSO to yield a 500 µM stock for labeling proteins in vitro.

  2. Set up the reactions, in order, as follows:
    Component Volume Final Conc.
    Phosphate Buffered Saline (PBS) 40 µl 1X
    50 mM DTT 1 µl 1 mM
    50 µM SNAP-tag Purified Protein 5 µl 5 µM
    500 µM SNAP-Cell Block 2 µl 20 µM
    250 µM SNAP-tag Substrate 2 µl 10 µM
    Total Volume 50 µl  
  3. Incubate sample containing only 20 µM SNAP-Cell Block in the dark for 20 minutes at 37°C. 

  4. Once incubation with SNAP-Cell Block is complete, add 2 µl of 250 µM SNAP-tag substrate, mix and incubate in the dark for 30 minutes at 37°C. 

  5. Run sample on an SDS-PAGE gel and detect using a fluorescent gel scanner or store samples at -20°C or -80°C in the dark.

    Removal of Unreacted Substrate (optional)
    After the labeling reaction the unreacted substrate can be separated from the labeled SNAP-tag fusion protein by gel filtration or dialysis. Please refer to the vendor’s instructions for the separation tools you are using.

    Notes for Labeling in vitro
    We recommend the routine addition of 1 mM DTT to all buffers used for handling, labeling and storage of the SNAP-tag. The stability of the SNAP-tag is improved in the presence of reducing agents; however it can also be labeled in their absence, if handling at temperatures above 4°C is minimized.

    SNAP-tag fusion proteins can be purified before labeling, but the labeling reaction also works in non-purified protein solutions (including cell lysates).

    For troubleshooting please refer to the instructions supplied with SNAP-Cell products as appropriate.