G Protein Beta Subunit Like Protein (GbL)

The predicted human GBL protein shares 96.6% amino acid identity with rat Gbl, which contains 7 WD40 repeats similar to those of G protein beta subunits. Immunoprecipitation of membrane and cytosolic fractions of transfected human embryonic kidney cells showed that rat Gbl was predominantly cytosolic.Loss-of-function experiments using small interfering RNA showed that, like MTOR and raptor, GBL participated in nutrient- and growth factor-mediated signaling to S6K1 (RPS6KB1), a downstream effector of MTOR, and in control of cell size. Binding of GBL to MTOR strongly stimulated MTOR kinase activity toward S6K1 and 4EBP1 (EIF4EPB1), and this effect was reversed by stable interaction of raptor with MTOR. Nutrients and rapamycin regulated the association of MTOR with raptor only in complexes that also contained GBL.