FIGURE 1.

Isothermal titration calorimetric analysis of the binding of a C-terminal peptide from SR-BI to individual recombinant PDZ domains of PDZK1. The indicated individual recombinant wild-type and mutant PDZ domains (0.03 mm in 1.8 ml of 150 mm NaCl, 0.5 mm tris(2-carboxyethyl)phosphine, 25 mm Tris, pH 8.0) were placed in a titration cell and equilibrated at 20 °C: PDZ1 (A), PDZ2 (B), PDZ3 (C), PDZ3 containing a Tyr²⁵³ → Ala substitution (D), and PDZ4 (E). A solution containing 0.3 to 1.0 mm of the C-terminal heptapeptide from SR-BI, ⁵⁰³VLQEAKL⁵⁰⁹, was injected in 10-μl aliquots with an interval of 4 min between each addition to permit re-equilibration. Titration curves were analyzed and K_d values were determined using ORIGIN 7.0 software.