Endoplasmic reticulum membrane protein that promotes endoplasmic reticulum-associated endosome fission (PubMed:30220460). Localizes to contact sites between the endoplasmic reticulum and endosomes and acts by promoting recruitment of the endoplasmic reticulum to endosome tubules for fission (PubMed:30220460). Endosome membrane fission of early and late endosomes is essential to separate regions destined for lysosomal degradation from carriers to be recycled to the plasma membrane (PubMed:30220460). . This is the function of TMCC1 (transmembrane and coiled-coil domain family 1, Ensembl gene identifier ENSG00000172765).