The HNOBA domain is found associated with the HNOB domain and Pfam:PF00211 in soluble cyclases and signalling proteins. The HNOB domain is predicted to function as a heme-dependent sensor for gaseous ligands, and transduce diverse downstream signals, in both bacteria and animals.

1: Ancient conserved domains shared by animal soluble guanylyl cyclases and bacterial signaling proteins. Iyer LM, Anantharaman V, Aravind L; BMC Genomics 2003;4:5. PMID:12590654