This family consists of a number of eukaryotic proteins including CXXC motif containing zinc binding protein (previously known as UPF0587 protein C1orf123). The crystal structure reveals that the protein binds a Zn2+ ion in a tetrahedral coordination with four Cys residues from two CxxC motifs. CXXC motif containing zinc binding protein was initially identified as an interaction partner for the heavy metal-associated (HMA) domain of CCS (copper chaperone for superoxide dismutase). However, it was shown that only misfolded mutant forms, lacking part of the zinc-binding sites, interact with CCS [1].

1: Identification of a novel zinc-binding protein, C1orf123, as an interactor with a heavy metal-associated domain. Furukawa Y, Lim C, Tosha T, Yoshida K, Hagai T, Akiyama S, Watanabe S, Nakagome K, Shiro Y; PLoS One. 2018;13:e0204355. PMID:30260988