Phospholipid scramblase involved in lipid homeostasis and membrane dynamics processes (By similarity). Has phospholipid scramblase activity toward cholesterol and phosphatidylserine, as well as phosphatidylethanolamine and phosphatidylcholine (By similarity). 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 (By similarity). Regulates ATP2A2 activity to control ER-isolation membrane contacts for autophagosome formation (PubMed:17940279). In addition to autophagy, involved in other processes in which phospholipid scramblase activity is required (By similarity). Modulates ER contacts with lipid droplets, mitochondria and endosomes (By similarity). Plays an essential role in formation of cell junctions (By similarity). Upon stress such as bacterial and viral infection, promotes formation of cytoplasmic vacuoles followed by cell death (PubMed:11785947, PubMed:12649568, PubMed:15367889). Involved in the cytoplasmic vacuolization of acinar cells during the early stage of acute pancreatitis (PubMed:11785947, PubMed:12649568, PubMed:15367889). a 1,2-diacyl-sn-glycero-3-phospho-L-serine(in) = a 1,2-diacyl-sn-glycero-3-phospho-L-serine(out) cholesterol(in) = cholesterol(out) a 1,2-diacyl-sn-glycero-3-phosphocholine(in) = a 1,2-diacyl-sn-glycero-3-phosphocholine(out) a 1,2-diacyl-sn-glycero-3-phosphoethanolamine(in) = a 1,2-diacyl-sn-glycero-3-phosphoethanolamine(out) Interacts with BECN1 (PubMed:17940279). Interacts with TJP1. Interacts with TP53INP2. Interacts with TMEM41B. Interacts with ATP2A2, PLN and SLN; competes with PLN and SLN to prevent them from forming an inhibitory complex with ATP2A2. Interacts with ATG2A (By similarity). Colocalizes with MAP1LC3A and BECN1. Highly expressed in intestine, kidney, ovary and placenta, moderately expressed in liver, lung, stomach, thymus, brain, and testis and slightly expressed in control thyroid and retina. Strongly expressed in pancreas (acinar cells) during acute pancreatitis. Overexpressed only in pancreas during acute pancreatitis. Up-regulated by starvation. Up-regulated following MTOR-inhibition by rapamycin. The VTT domain was previously called the SNARE-assoc domain. As there is no evidence that this domain associates with SNARE proteins, it was renamed as VMP1, TMEM41, and TVP38 (VTT) domain. Belongs to the VMP1 family.