Structural basis for the specificity of PPM1H phosphatase for Rab GTPasesLRRK2 serine/threonine kinase is associated with inherited Parkinson’s disease. LRRK2 phosphorylates a subset of Rab GTPases within their switch 2 motif to control their interactions with effectors. Recent work has shown that the metal-dependent protein phosphatase PPM1H counteracts LRRK2 by dephosphorylating Rabs. PPM1H is highly selective and closely related PPM1J exhibits no activity toward substrates such as Rab8a phosphorylated at Thr72 (pThr72). Here we have identified the structural determinant of PPM1H specificity for Rabs. The crystal structure of PPM1H reveals that it is a dimer, confirmed by biophysical analysis, and possesses a conserved catalytic domain that strikingly has evolved a 110-residue flap domain adjacent to the active site. The flap domain distantly resembles tudor domains that interact with histones in the context of epigenetics. Cellular assays, crosslinking and 3-D modelling suggest that the flap domain encodes the docking motif for phosphorylated Rabs. Consistent with this hypothesis, a PPM1J chimaera with the PPM1H flap domain dephosphorylates pThr72 of Rab8a both in vitro and in cellular assays. Therefore, PPM1H has acquired a Rab-specific...Access is restricted by the data custodian. The collection's description and structure are public; the data is not available for querying through this network.Structural basis for the specificity of PPM1H phosphatase for Rab GTPases is published on Viral AI.