GTPase tethering membranes through formation of trans-homooligomers and mediating homotypic fusion of endoplasmic reticulum membranes. Functions in endoplasmic reticulum tubular network biogenesis (By similarity). Interacts with ZFYVE27 (By similarity). Interacts with REEP5 (PubMed:32075961). Localizes to endoplasmic reticulum tubules and accumulates in punctuate structures corresponding to 3-way junctions, which represent crossing-points at which the tubules build a polygonal network. Expressed in cardiomyocytes (at protein level). Belongs to the TRAFAC class dynamin-like GTPase superfamily. GB1/RHD3 GTPase family. GB1 subfamily.