Fig. 3. Photo-controlled TAP inhibition by pc-ICP47 variants. (a) Binding of the reporter peptide C4F to TAP was competed with increasing concentrations of ICP472–34 or pc-ICP472–34 variants. Unmodified ICP47 (Ki = 100 ± 11 nM) and pc-ICP47 with the photo-cleavable amino acid at position 15 have very similar IC50 values (15R-Anp, Ki = 121 ± 9 nM; 15S-Anp, Ki = 125 ± 8 nM), whereas lower inhibition constants were observed for pc-ICP4714Anp variants (14R-Anp, Ki = 550 ± 35 nM; 14S-Anp, Ki = 489 ± 22 nM). (b) Peptide binding was blocked with 100 μM of pc-ICP4715Anp2–34 and unmodified ICP472–34. After photo-cleavage at 365 nm, peptide binding to TAP was restored (>80%) for both pc-ICP4715Anp2–34, while illumination of unmodified ICP472–34 did not recover the TAP activity.
