Fig. 3.
TAPBPR augments peptide binding by HLA-A2. (A) TAPBPR/HLA-A2 complexes (red), HLA-A2/FluM158–66 complexes (black), or TAPBPR alone (blue) at the indicated protein concentrations were offered either a high-affinity, fluorescent peptide [FITC-HBV18–27 (circles)], or a control fluorescent peptide [FITC-PAP277–285 (squares)] at 10 nM. (B) The HLA-A2/FluM158–66 exchange of peptide with fluorescent peptide is augmented by TAPBPR. Purified HLA-A2/FluM158–66 complexes were mixed in the indicated amounts with 10 nM FITC-HBV18–27 with or without additional purified recombinant TAPBPR, and FP was measured as described in Materials and Methods. Circles represent data points, and curves represent best fits. Graded concentrations of TAPBPR ranged from 0 (black), 3.9 (red), 7.8 (light blue), 15.6 (green), 31.2 (magenta), 62.5 (orange), 125 (brown), 250 (red), and 500 nM (blue). (C) HLA-A2/HBV18–27 complexes were similarly prepared and purified and analyzed with the same FITC-HBV18–27 peptide as in C. The family of curves is coded for the same concentrations of TAPBPR as in B. (D) No exchange of fluorescent peptide is observed when the probe peptide does not bind HLA-A2. Peptide FITC-PAP277–285 at 10 nM was used to test for exchange with HLA-A2/FluM158–66 complexes in the absence or presence of graded concentrations of TAPBPR. All experiments shown are representative of at least three similar ones.