Phospholipid scramblase involved in lipid homeostasis and membrane dynamics processes. Has phospholipid scramblase activity toward cholesterol and phosphatidylserine, as well as phosphatidylethanolamine and phosphatidylcholine. Required for autophagosome formation: participates in early stages of autophagosome biogenesis at the endoplasmic reticulum (ER) membrane by reequilibrating the leaflets of the ER as lipids are extracted by ATG2 (ATG2A or ATG2B) to mediate autophagosome assembly. In addition to autophagy, involved in other processes in which phospholipid scramblase activity is required. Required for normal motor neuron development.; (Microbial infection) Critical host factor required for infection by human coronaviruses SARS-CoV-2, HCoV-OC43, HCoV-NL63, and HCoV-229E, as well as all flaviviruses tested such as Zika virus and Yellow fever virus. Required post-entry of the virus to facilitate the ER membrane remodeling necessary to form replication organelles.