Table 3.
SPR analysis of CD4 peptide–adaptor complex binding
| CD4 peptide | Sequence |
KD (μM)
|
|
|---|---|---|---|
| AP-1 | AP-2 | ||
| wt | Biotin-RHRRRQAERMSQIKRLLSEK | ND | 92 |
| L413A/L414A | Biotin-RHRRRQAERMSQIKRAASEK | ND | ND |
| S408 | Biotin-RHRRRQAERMSQIKRLLSEK | 0.60 | 0.12 |
| S415 | Biotin-RHRRRQAERMSQIKRLLSEK | 0.76 | 0.35 |
| S408/S415 | Biotin-RHRRRQAERMSQIKRLLSEK | 0.52 | 0.08 |
| S408/L413A/L414A | Biotin-RHRRRQAERMSQIKRAASEK | ND | 82 |
| S408/S415/L413A/L414A | Biotin-RHRRRQAERMSQIKRAASEK | 46 | 12 |
| S408E/L413A/L414A | Biotin-RHRRRQAERMEQIKRAASEK | 86 | ND |
CD4 cytoplasmic domain peptides were immobilized on streptavidin-coated sensor chips at similar densities (variation, <8%). Purified AP-1 and AP-2 complexes were used at concentrations ranging from 50 to 500 nM. The equilibrium constant (KD = the association rate [ka]/dissociation rate [kd]) was calculated from the sensorgrams (see Fig. 7) as described in MATERIALS AND METHODS. Phosphoserine residues are indicated in underlined type; ND, reactions in which the interactions were too weak to determine the binding constants.