CDC50A functions as an essential accessory subunit for P4-ATPase phospholipid flippases, facilitating the translocation of aminophospholipids from the outer to inner leaflet of cellular membranes 1. As a terminal-glycosylated transmembrane protein, CDC50A is ubiquitously expressed and localizes to various cellular compartments including the trans-Golgi network, secretory vesicles, and plasma membrane 2. The protein's extracellular domain contains evolutionarily conserved residues critical for both chaperoning P4-ATPases to their membrane destinations and inducing their ATP hydrolysis-coupled flippase activity 1. CDC50A forms functional complexes with multiple P4-ATPases including ATP8B1, ATP8B2, ATP10A, and ATP11C, which collectively maintain phospholipid asymmetry essential for cellular homeostasis 34. Loss of CDC50A function disrupts phosphoinositide homeostasis at the plasma membrane and affects natural killer cell-mediated cytotoxicity through altered phosphatidylserine exposure 35. Clinically, CDC50A expression correlates with cancer-initiating cell properties in epithelial ovarian cancer and shorter platinum-free intervals, suggesting its potential as a therapeutic biomarker 6. The protein is also exploited by pathogens like Newcastle disease virus to facilitate viral replication through manipulation of membrane lipid asymmetry 7.