Fig. (1) PCSK9-HT is labeled with HaloTag ligands TMR and Alexa Fluor 488. A Huh7 stable cell line expressing C-terminal PCSK9-HaloTag fusion protein was established and verified with western blot (A, clone 14-13-E4). The expression level of PCSK9-HT is about 2-fold of the endogenous PCSK9 level. B. Purified PCSK9-HT inhibited LDL uptake in a dose dependent manner in HepG2 cells. The de-creased potency of PCSK9-HT (red) compared to wt PCSK9 (blue) is likely due to protein impurity. C. 14-13-E4 cells were labeled with 0.2 µM Alexa Fluor 488 overnight, followed by TMR labeling (5 µM) for 15 min. The unbound ligand was washed off before the second label-ing or image capture. Confocal images were taken with a Zeiss LSM 510 confocal microscope with appropriate fluorescence filters. Intracel-lular PCSK9 (red) and internalized PCSK9 (green) showed different staining patterns.