Catalyzes the conversion of GTP to GDP through hydrolysis of the gamma-phosphate bond in GTP (By similarity). Binds to microtubules and promotes microtubule polymerization and bundling. GTPase activity is not necessary for these microtubule-related functions (PubMed:28855639). GTP + H2O = GDP + H(+) + phosphate Expressed in many adult amd embryonic tissues. In adults, highest levels in ovaries and testes, followed by skeletal muscle, stomach, brain, kidney and liver. Weak expression in heart and brain. At stage 22, expressed in blood islands, somites, eyes, trunk neural crest, mandibular crest segment, hyoid crest segment and branchial crest segment. At stage 32, expressed in otic vesicle, pronephros, forebraiin, midbrain, hindbrain, branchial arch, eyes, lens, spinal cord and notochord. Belongs to the TRAFAC class OBG-HflX-like GTPase superfamily. OBG GTPase family.