SNAP-tag Technology
Purpose
SNAP-tag labeling is an ideal way to identify and observe proteins in an organism through the creation of fusion proteins. Most other fusion protein labeling devices face two major concerns, either they are limited to labeling methods that can be genetically encoded into an organism or they are specified to only be used in the study of a single type of protein without the ability to diversify. SNAP-tag labeling overcomes these problems seen in other fusion protein labeling methods by relying on tags that can be labeled with synthetic probes (which allow for better visualization than natural probes) and by having the ability to work as a labeling method for about any protein since they are chemically inert towards proteins other than benzylguanine (BG) derivatives. The SNAP-tag protein (a 20kD mutant alkylguanine-DNA-alkyltransferase) is able to fuse to a protein of interest and not affect the function of most of these the protein. This allows for SNAP-tag labeling to help with the visualization and study of proteins in living cells.
Discovery
Jon Beckwith is credited along with a group of scientists as being a pioneer in developing fusion proteins that could be easily tagged in a way that didn't inhibit the function of the proteins. In 1980 this type of tagging was first performed by fusing β-galactosidase to the cytoplasmic membrane protein MalF to help facilitate this proteins eventual purification. Following this experiment, a multitude of tags have emerged and become popular in various branches of biology. The eventual development of the SNAP-tag protein would soon follow and its ability to far exceed other tagging methods have lead to its prominent use in protein tagging.
How SNAP-tag Works
In order to tag a protein with SNAP-tag technology one must first create a fusion protein that includes a SNAP protein(mutant alkylguanine-DNA-alkyltransferase). To create this type of fusion protein an individual will need a vector that includes the SNAP26b gene along with restriction sites down stream of this specific gene. This will allow for an individual to subclone any gene of interest into the regions downstream of the SNAP26b gene, which creates the highest probability for N- or C-terminal fusion occurring correctly between the SNAP protein and the protein that's being tagged. The prepared plasmid vector can then be transformed into a cell to clone the fusion protein. Once the fusion protein is expressed in an observable concentration an individual will need to introduce a benzylguanine (BG) derivative that has been tagged with a fluorescent particle. Benzylguanine (BG) derivatives interact with alkylguanine-DNA-alkyltransferase (or SNAP proteins) in a way that results in the formation of a stable thioether bond between a reactive cysteine residue the tag and the probe. Allowing for visualization of the protein of interest that had its gene originally subcloned into the plasmid vector. https://www.youtube.com/watch?v=NBRk3f6q-_M (Link to video on SNAP-tag Applications and other Basics)
Advantages/Disadvantages of SNAP-tag Technology
| Advantages | Disadvantages |
|---|---|
| It can use synthetic probes such as fluorophores or affinity labels which allow for better visualization of proteins | Some proteins that are fused to the SNAP protein have a change in function that occurs |
| Labeling with SNAP-tag is irreversible and quantitative, making it better suited for the detection and quantitation of labeled proteins via in-gel fluorescence scanning of SDS-PAGE gels | Once the fluorescent tag has been bound its irreversible so no other activities to the protein can be undertaken |
| SNAP-tag proteins can be labeled at both cell surfaces and within cells | |
| SNAP-tag proteins are inert to all proteins other than Benzylguanine (BG) derivatives and they don't usually effect protein function |