T-cell surface glycoprotein CD3 zeta chain is a transmembrane protein belonging to the CD3 ? (zeta)/FCER1G family, also known as T-cell receptor T3 zeta chain or CD247 (Cluster of Differentiation 247). This protein is part of a protein complex together with the T cell receptor (TCR), which can recognize various antigens with major histocompatibility complex (MHC) molecules. The structure of zeta transmembrane dimer consists of a left-handed coiled coil with polar contacts.