Atlastan

Atlastan is a term occasionally used to refer to atlastin, a family of endoplasmic reticulum (ER) membrane–anchored GTPases that mediate homotypic fusion of ER tubules. The spelling atlastan appears in some sources as an alternate transliteration or misspelling of atlastin, and this article treats it as referring to the same protein family.

Biological role and function: Atlastins, including the paralogs ATL1, ATL2, and ATL3, are essential for the formation and maintenance of the interconnected ER network in vertebrate cells. They function as dimeric GTPases: two molecules bind GTP, dimerize, and tether opposing ER membranes; subsequent GTP hydrolysis drives conformational changes that promote membrane fusion. This activity supports ER morphology, distribution of ER contact sites, and proper lipid and protein trafficking within the network.

Structure and mechanism: Each atlastin protein has a cytosolic N-terminal GTPase domain, followed by a three-helix middle domain, and a pair of C-terminal transmembrane helices that anchor the protein in the ER membrane, with a short luminal tail. Dimerization occurs via the GTPase and middle domains, and GTP binding and hydrolysis couple to the mechanical steps that fuse ER membranes.

Genetics and disease: In humans, ATL1, ATL2, and ATL3 encode the atlastin paralogs. Variants in these genes have been associated with hereditary spastic paraplegia and related neurodegenerative conditions, reflecting the importance of ER network integrity for axonal transport and neuron function. Experimental models show that loss or alteration of atlastin disrupts ER architecture and cellular organization.

Discovery and terminology: The proteins are commonly referred to as atlastin-1 (ATL1), atlastin-2 (ATL2), and atlastin-3 (ATL3). The term atlastan is sometimes used as an alternate spelling, but standard references describe the same gene family and its cellular role. See also Atlastin.