CLIP-Cell™ Fluorescein is a green fluorescent substrate that can be used to label CLIP-tag™ fusion proteins inside living cells or in vitro. This cell-permeable substrate (BC-PF) is based on dipivaloylfluorescein and is suitable for standard fluorescein filter sets. Dipivaloylfluorescein is essentially non-fluorescent, but it becomes fluorescent inside the cell when it is hydrolyzed by non-specific esterases, yielding fluorescein. It has an excitation maximum at 500 nm and emission maximum at 524 nm. This substrate has limited photostability. If this presents a problem, we recommend using CLIP-Cell 505, which has similar spectral characteristics, but much greater photostability. This package includes 50 nmol of CLIP-Cell Fluorescein substrate, sufficient to make 10 ml of a 5 µM CLIP-tag fusion protein labeling solution.
The CLIP-tag protein labeling system enables the specific, covalent attachment of virtually any molecule to a protein of interest. CLIP-tag is a protein tag based on human O6-alkylguanine-DNAalkyltransferase (hAGT). CLIP-tag substrates are derivatives of benzylcytosine (BC). In the labeling reaction, the substituted benzyl group of the substrate is covalently attached to the reactive cysteine of CLIP-tag forming a stable thioether bond. Although CLIP-tag is based on the same protein as SNAP-tag®, the benzylcytosine substrates form a separate class of substrates, different from the benzylguanine substrates recognized by SNAP-tag. CLIP-tag and SNAP-tag can be used for orthogonal and complementary labeling of two proteins simultaneously in the same cells.
There are two steps to using this system: subcloning and expression of the protein of interest as a CLIP-tag fusion, and labeling of the fusion with the CLIP-tag substrate of choice. Expression of CLIP-tag fusion proteins is described in the documentation supplied with CLIP-tag plasmids. The labeling of the fusion proteins with the CLIP-tag substrate is described in this document.
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