The DM13 domain is a component of a novel electron-transfer system potentially involved in oxidative modification of animal cell-surface proteins [1]. It contains a nearly absolutely conserved cysteine, which could be involved in a redox reaction, either as a naked thiol group or through binding a prosthetic group like heme [1].

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