Guanine nucleotide dissociation inhibitor (GDI) which functions as a receptor-independent activator of heterotrimeric G-protein signaling. Keeps G(i/o) alpha subunit in its GDP-bound form thus uncoupling heterotrimeric G-proteins signaling from G protein-coupled receptors. Controls spindle orientation and asymmetric cell fate of cerebral cortical progenitors. May also be involved in macroautophagy in intestinal cells. May play a role in drug addiction. Interacts with GNAI1, GNAI2 and GNAI3 preferentially in their GDP-bound state. May also interact with GNAO1. Interacts with STK11/LKB1 and MACF1 (By similarity). Interacts with INSC/inscuteable and FRMPD1. Expressed in intestinal cells. The GoLoco domains mediate interaction with G(i/o) alpha (By similarity). The GoLoco domains are essential for the GDI activity toward G(i/o) alpha. Phosphorylation regulates interaction with G(i/o) alpha. Minor isoform. Major isoform. Belongs to the GPSM family. Truncated N-terminus. Truncated N-terminus.