TackOD1 (Thaumarchaeal output domain 1) is a predicted metal-binding domain found in archaea and in some bacteria. It contains 11 highly conserved Cys residues, which form 5 CxxC motifs and an HxxC motif. In several instances, it is found in combination with the Response_reg Pfam:PF00072 domain (Galperin et al., 2018, Phyletic distribution and lineage-specific domain architectures of archaeal two-component signal transduction systems).