As shown in eq 1, interconversion between one or more inactive conformations, E′, and the conformation competent for binding substrate, E, determines the equilibrium population of active enzyme.
This implies that the mutant stabilizes the active more than the inactive conformation, consistent with a higher constitutive activity of the mutant with respect to the wild-type receptor.
Breaking of these interactions by the M398T mutation would destabilize the inactive conformation more than the active conformation and this is consistent with a 25-fold increase in constitutive activity compared to the wild-type receptor (Table 3).
Thereby, the enzyme would be kept in an inactive conformation more efficiently when bound to mismatched C rather than mismatched 5mC, resulting in a favored extension of 5mC.
For instance, Vivanco et al. [ 3] indicated that therapeutic failure may be in part explained by insufficient levels of EGFR inhibition, and that targeting its inactive conformation may be a more effective strategy.
Selective kinase targeting can be easier achieved within type II inhibitors, because more variability is seen among kinases in their inactive conformation [ 60].
Based on previous experiments published by the authors, the data are interpreted with a model in which the new compound shifts the equilibrium between the active and inactive conformation of the kinase much more towards the active state.
Kinases undergo conformational changes between active and inactive conformation and thus an additional hydrophobic pocket is created in the inactive conformation where the surrounding amino acids are less conserved [2].
Moreover, one set of direct gefitinib-binding studies suggested that this TKI binds more tightly to the activated (L834R) EGFR-TKD than to the inactive conformation [ 11].
The active conformation of Pak1, containing only the catalytic domain, shows a conformational change in the activation loop as compared to the inactive conformation [21].
