Fig 2: Characterization of Nanofitins targeting the LepR. (A) Signals obtained in a competition ELISA with Nanofitins tested on immobilized rhLepR in the presence or absence of leptin. (B) Signals obtained with a cross-reactivity ELISA with Nanofitins tested on immobilized rhLepR or rmLepR. Signal ratio of 1:1 is indicated by a black line, with a delimitation of ±0.25 absorbance units.

Fig 3: Ex vivo transport experiments across porcine intestinal tissue performed with (A) labeled anti-LepR Nanofitins 1-F08 (n = 10), 1-D07 (n = 4), and an irrelevant Nanofitin (n = 6) at 90 µM; (B) labeled 1-F08 at 90 µM in the presence of a 9-fold excess of unlabeled 1-F08 (1-F08 + excess of 1-F08, n = 6) or unlabeled irrelevant Nanofitin (1-F08 + excess of Irr-NF, n = 8); or (C) labeled 1-F08-NF2 (n = 4) and labeled irrelevant NF-NF2 (Irr NF-NF2, n = 5) tested at 90 µM. The masses used to calculate the percentages of initial donor transported were determined by fluorescence. The percentages of Nanofitin transported (B) were normalized with the percentage of labeled 1-F08 transported in the absence of an excess of unlabeled Nanofitin. Results are expressed as mean values ± SD (unpaired Student’s t-test; ** p < 0.01, *** p < 0.001).

Fig 4: Biochemical analysis of human leptin variants constructed in this study. (A, B) Receptor activation on HEK cells transfected with the human LEPRb gene together with a STAT3-responsive Photinus luciferase and a constitutively expressed Renilla luciferase (for signal normalization). Cells were stimulated with (A) recombinant unmodified or (B) PASylated leptin variants (50 fM–500 nM), followed by measurement of JAK/STAT activation using a dual luciferase assay. (C) Real-time SPR binding analysis of PAS(200)-huLeptinW100Q to its target human LepRb, which was immobilized as Fc-fusion protein on the sensorchip. (D) Thermal unfolding of PASylated leptin variants monitored by CD spectroscopy at 222 nm (curve fits shown as solid lines).