Effect of the distal C162S mutation on the energetics of drug binding to p38α MAP kinase

The binding reactions of the inhibitor drugs, SB 203580, SKF 86002, and p38 INH.1 to the isoforms 1 and 2 splice variants of p38α MAP kinase and their C162S mutants, as determined from ITC measurements from 25 to 35 °C, are totally enthalpically driven with binding constants ranging from 107 M−1 for SKF 86002 and SB 203580 to 109 M−1 for p38 INH.1. Interactions of p38 INH.1 with an additional hydrophobic pocket of the kinase would account for its large increase in Kb. DSC scans exhibited single unfolding transitions for the isoforms, their mutants, and the mutants bound to the drug inhibitors. Two transitions, however, were observed for the isoform–drug complexes of SB 203580 and p38 INH.1 and were attributed to decoupled unfolding of the N- and C-terminal domains of the kinase. The C-terminal domain of isoform 1 is estimated to be less stable than of isoform 2 by 15 kJ mol−1.