Figure 1.

Characterization of a releasable SNAP-tag probe. (a) Schematic of BG-S-S-488, with O⁶-benzylguanine (blue), Alexa Fluor 488 (green), and disulfide linkage (red) highlighted. (b) Comparison of sensitivity of BG-S-S-488 versus SNAP-Surface 488 (New England Biolabs) to TCEP in HeLa cells transfected with SNAP-β2ADR. Scale bar, 10 μm. (c) Comparison of the ability of unesterified TCEP versus tmTCEP to cleave intracellular BG-S-S-488. Free label is extracted by TX-100 from endosomes in cells incubated with tmTCEP. Scale bar, 10 μm. (d) Fluorescence time course showing sensitivity of BG-S-S-488 to different TCEP concentrations in live COS cells transfected with SNAP-β2ADR. Measurements were taken in the absence of endocytosis, so that only cell surface fluorescence was quantified.