Human zonula occludens 2 (ZO-2) protein is a multi-domain protein that consists of an SH3 domain, a GK domain and three copies of a PDZ domain with slight divergence. The three PDZ domains act as protein-recognition modules that may mediate protein assembly and subunit localization. The crystal structure of the second PDZ domain of ZO-2 (ZO-2 PDZ2) was determined by molecular replacement at 1.75 A resolution, revealing a dimer in the asymmetric unit. The dimer is stabilized by extensive symmetrical domain-swapping of the beta1 and beta2 strands. Structural comparison shows that the ZO-2 PDZ2 homodimer may have a similar ligand-binding pattern to the ZO-1 PDZ2-connexin 43 complex.