The incorporation of the zetazeta signalling module requires one basic TCR alpha and two zetazeta aspartic acid TM residues. The structure of the zetazeta(TM) dimer consists of a left-handed coiled coil with polar contacts. Two aspartic acids are critical for zetazeta dimerization and assembly with TCR.
Jiyao W et al.(2023). "The conserved domain database in 2023.",