GTPase tethering membranes through formation of trans-homooligomers and mediating homotypic fusion of endoplasmic reticulum membranes. Functions in endoplasmic reticulum tubular network biogenesis. May also regulate Golgi biogenesis. May regulate axonal development. Monomer as apoprotein and in the GDP-bound form. Homodimer in the GTP-bound form. Homooligomer. Interacts (via N-terminal region) with MAP4K4 (via CNH regulatory domain). Interacts with SPAST; interaction is direct (By similarity). Interacts with REEP5, RTN3 and probably RTN4 (via the transmembrane region) (PubMed:19665976). Interacts with REEP1. Interacts with CPT1C. Interacts with ARL6IP1 (By similarity). Interacts with ZFYVE27 (PubMed:24668814). Localizes to endoplasmic reticulum tubular network. Belongs to the TRAFAC class dynamin-like GTPase superfamily. GB1/RHD3 GTPase family. GB1 subfamily.