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. Author manuscript; available in PMC: 2014 Jun 1.
Published in final edited form as: Curr Protoc Chem Biol. 2013 Jun;5(2):131–155. doi: 10.1002/9780470559277.ch130019

Figure 1.

Figure 1

Cartoon of TMP-tags. (A) Non-covalent TMP-tag is based on the high-affinity interaction between E. coli dihydrofolatereductase (eDHFR) and the antibiotic trimethoprim (TMP). The target protein (purple) is tagged with eDHFR (blue) and then labeled with a cell-permeable TMP-fluorophore (F) heterodimer. (B) The TMP-tag is rendered covalent by installing a nucleophilic amino acid near the binding pocket to react with a latent electrophile (acrylamide) when TMP binds to eDHFR. (C) The fluorogenic TMP-tag centers a TMP-quencher (Q) –fluorophore (F) heterotrimer. When TMP binds to eDHFR, the nucleophilic amino acid near the binding pocket initiated a proximity-induced SN2 reaction that cleaves the electrophile attached to the quencher and thus switches on the fluorophore.