Fig. 2
p2TA binds directly to CD28. A, B Representative surface plasmon resonance responses for binding of CD28-IgG-Fc to immobilized peptides p2TA (700 resonance units) (A) and pe12 (1260 resonance units) (B) (top panels); KD, 4 and 3 µM, respectively. Analyte concentrations increased in twofold increments from 0.2 µM. Representative surface plasmon resonance responses for binding of IgG-Fc to immobilized p2TA and pe12 are shown in bottom panels; analyte concentrations increased in twofold increments from 0.125 µM. C Representative surface plasmon resonance responses for binding of disulfide-linked homodimeric CD28 extracellular domain protein without Fc (CD28) to immobilized p2TA (733 resonance units). Analyte concentrations increased in twofold increments from 0.125 µM; KD, 3.4 µM. D The p2TA, p5TA and p4TA regions at the homodimer interface of CD28. In the sequence of the extracellular domain of CD28, dimer interface contact residues are shown in red color, peptide sequences p2TA, p4TA and p5TA are highlighted in yellow, and the αCD28 epitope [13] is underlined. In structure model of the extracellular domain of costimulatory receptor CD28 (green; 1yjd.pdb), a single beta-barrel, region of p2TA is shown in sticks in dark blue with 2 dimer interface contacts in orange, region of p5TA is in red with 4 dimer interface contacts in yellow and on the right the HVK sequence shared with the epitope, and region of p4TA is in cyan with 3 dimer interface contacts in orange