CD98 is a single-pass type I I membrane protein which belongs to the SLC3A transporter family. SLC3A2/MDU1 is expressed ubiquitously in all tissues tested with highest levels detected in kidney, placenta and testis and weakest level in thymus. It consists of an 85 kDa glycosylated type II transmembrane heavy chain and a 40-50 kDa non-glycosylated light chain with 12 transmembrane segments. The heavy chain (SLC3A2) pairs with one of several light chains (SLC7A5, 6, 7, 8, 10, or 11) and is required for the cell surface expression and amino acid transport function of the light chains. It is involved in guiding and targeting of LAT1 and LAT2 to the plasma membrane. It also mediates integrin signaling, T cell costimulation, B cell proliferation, and viral fusion with cell membranes.