GTPase tethering membranes through formation of trans-homooligomers and mediating homotypic fusion of endoplasmic reticulum membranes. Functions in endoplasmic reticulum tubular network biogenesis (PubMed:27619977). May also regulate Golgi biogenesis. May regulate axonal development. Monomer as apoprotein and in the GDP-bound form. Homodimer in the GTP-bound form. Interacts (via N-terminal region) with MAP4K4 (via CNH regulatory domain). Interacts with REEP5, RTN3 and RTN4 (via the transmembrane region). Interacts with SPAST; interaction is direct. May interact with TMED2. Interacts with REEP1. Interacts with CPT1C. Interacts with ARL6IP1 (By similarity). Interacts with ZFYVE27 (PubMed:23969831). Localizes to endoplasmic reticulum tubular network (PubMed:27619977). Expressed predominantly in the adult and fetal central nervous system. Measurable expression in all tissues examined, although expression in adult brain is at least 50-fold higher than in other tissues. Detected predominantly in pyramidal neurons in the cerebral cortex and the hippocampus of the brain. Expressed in upper and lower motor neurons (at protein level). The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the TRAFAC class dynamin-like GTPase superfamily. GB1/RHD3 GTPase family. GB1 subfamily. Extended N-terminus. Truncated N-terminus.