The DOMON (named after dopamine beta-monooxygenase N-terminal) domain is 110-125 residues long. It is predicted to form an all beta fold with up to 11 strands and is secreted to the extracellular compartment. The beta-strand folding produces a hydrophobic pocket which appears to bind soluble haem. This is consistent with the predominant architectures where the protein is associated with cytochromes or enzymatic domains whose activity involves redox or electron transfer reactions potentially as a direct participant in the electron transfer process. The DOMON domain superfamily, of which this is just one member, shows (1) multiple hydrophobic residues that contribute to the hydrophobic core of the strands of the beta-sandwich, and small residues found at the boundaries of strands and loops, (2) a strongly conserved charged residue (usually arginine/lysine) at the end of strand 9, which possibly stabilises the loop between 9 and 10, and (3) a polar residue (usually histidine, lysine or arginine), that interacts or coordinates with ligands [1]. The suggested superfamily includes both haem- and sugar-binding members: the haem-binding families being the ethyl-Benzoate dehydrogenase family EB_dh, Pfam:PF09459, the cellobiose dehydrogenase family CBDH and this family, and the sugar-binding families being the xylanases, CBM_4_9, Pfam:PF02018. The common feature of the superfamily is the 11-beta-strand structure, although the first and eleventh strands are not well conserved either within families or between families.

1: The DOMON domains are involved in heme and sugar recognition. Iyer LM, Anantharaman V, Aravind L; Bioinformatics. 2007;23:2660-2664. PMID:17878204