Allosteric inhibition of the guanine nucleotide exchange factor DOCK5 by a small molecule

Rac small GTPases as well as their GEFs from the Pier family are pivotal checkpoints in development, autoimmunity and bone homeostasis, as well as their abnormal regulation is connected to diverse pathologies. Small molecules that hinder their activities are thus required to investigate their functions. Here, we characterised the mechanism of inhibition of human DOCK5 by C21, a little molecule that inhibits mouse Dock5 in cells and blocks bone degradation in rodents types of brittle bones. We demonstrated the catalytic DHR2 domain of DOCK5 includes a high basal GEF activity even without the membranes which isn’t controlled with a simple feedback loop. C21 blocks this activity inside a non-competitive manner and it is specific for DOCK5. In comparison, another Pier inhibitor, CPYPP, inhibits both DOCK5 as well as an unrelated GEF, Trio. To achieve understanding of structural options that come with the inhibitory mechanism of C21, we used SAXS analysis of DOCK5DHR2 and crystallographic analysis of unbound Rac1-GDP. Together, these data claim that C21 uses intramolecular dynamics of DOCK5 and Rac1 to rework the complex into an unproductive conformation. According to this allosteric mechanism, we advise that diversion of intramolecular dynamics is really a potent mechanism for that CPYPP inhibition of multidomain regulators of small GTPases.