The Evolution of SNAP-Tag Labels.

The conjugation of proteins with synthetic molecules can be conducted in many different ways. In this Perspective, we focus on tag-based techniques and specifically on the SNAP-tag technology. The SNAP-tag technology makes use of a fusion protein between a protein of interest and an enzyme tag that enables the actual conjugation reaction. The SNAP-tag is based on the O 6 -alkylguanine-DNA alkyltransferase (AGT) enzyme and is optimized to react selectively with O 6 -benzylguanine (BG) substrates. BG-containing dye derivatives have frequently been used to introduce a fluorescent tag to a specific protein. We believe that the site-specific conjugation of polymers to proteins can significantly benefit from the SNAP-tag technology. Especially, polymers synthesized via reversible deactivation radical polymerization allow for the facile introduction of a BG end group to enable SNAP-tag conjugation.