The [zeta] CA active site resembles that of [beta] Cas coordinating the metal ion to a His and two Cys residues (x, x+52, x+62, where x=263 in CDCA1) [45].
Crystals structures of [zeta] CAs are limited to CDCA1. CDCA1 has three tandem repeats (R1-R3), each of which is enzymatically active and mimics the structure of [beta] CA dimer.