Starch binding domain-containing protein 1 (Stbd1) has been associated with glycogen trafficking and metabolism, and has been linked to autophagy through its interaction with autophagy proteins, as well as through a binding motif. It was thus proposed that Stbd1 is a selective autophagy receptor for glycogen trafficking to lysosomes. On page 903, Petros Petrou and co-workers explore the functions of Stbd1 in HeLa cells and show that it resides at the endoplasmic reticulum (ER), also localising to mitochondria-associated membranes – the sites of ER-mitochondria contacts. When overexpressed, Stbd1 induces morphological changes in both the ER and mitochondrial network, and the formation of organised ER structures. The authors find that Stbd1 is N-myristoylated. Lack of N-myristoylation promotes its subcellular localisation to ER–mitochondria contact sites, for which Stbd1 binding to glycogen is essential. Non-myristoylated Stbd1 increases ER–mitochondria association and leads to fragmented mitochondria. Conversely, knockdown of Stbd1 provokes a weakening of ER–mitochondria tethers and changes in mitochondria morphology with fewer and more-elongated mitochondria present in the cells. The work describes a new role for Stbd1 at ER–mitochondria contact sites and highlights the molecular mechanism for the cellular localisation of Stbd1.
