Probable pseudophosphatase. Lacks several amino acids in the catalytic pocket which renders it catalytically inactive as a phosphatase. The pocket is however sufficiently preserved to bind phosphorylated substrates, and maybe protect them from phosphatases. Inhibits myoblast differentiation in vitro and induces oncogenic transformation in fibroblasts. May function as a guanine nucleotide exchange factor (GEF) activating RAB28. Promotes the exchange of GDP to GTP, converting inactive GDP-bound Rab proteins into their active GTP-bound form.