Skip to main content
. 2020 Nov 5;370(6521):1208–1214. doi: 10.1126/science.abe0075

Fig. 2. Stability and binding of the de novo protein decoys CTC-445, CTC-445.2, and CTC-445.2d.

Fig. 2

(A) Design models of CTC-445, CTC-445.2, and CTC-445.2d. CTC-445.2 contains five mutations that were guided by directed evolution experiments. CTC-445.2d is a bivalent variant composed of two CTC-445.2 subunits linked by a 16-mer flexible GS linker (sequence -GGGSGGSGSGGSGGGS-). (B) Circular dichroism of recombinantly expressed CTC-445 (red), CTC-445.2 (blue), and CTC-445.2d (orange). Thermally induced melting of the decoys was followed by its circular dichroism signal at 208 nm (heating rate, 2°C/min). The inset shows far ultraviolet (UV) wavelength spectra at 20°C (purple), after heating to ~95°C (brown), and after cooling the heated sample to 20°C (green dashed). Complete ellipticity spectra recovery (full reversibility) upon cooling was observed in all cases. Calculated Tm values for CTC-445, CTC-445.2, and CTC-445.2d are 75.3 ± 0.2°C, ≈93°C, and 71.7.± 0.2°C, respectively. (C) Binding was assessed using biolayer interferometry (OCTET) binding assays of CTC-445, CTC-445.2, and CTC-445.2d against immobilized SARS-CoV-2 RBD (top) or SARS-CoV-1 RBD (bottom) (see table S1). The model fitting is shown with dotted black lines.