NosD is a periplasmic protein which is thought to insert copper into the exported reductase apoenzyme (NosZ) [1]. This region forms a parallel beta helix domain.

1: Identification and analysis of the dissimilatory nitrous oxide reduction genes, nosRZDFY, of Rhizobium meliloti. Holloway P, McCormick W, Watson RJ, Chan YK; J Bacteriol 1996;178:1505-1514. PMID:8626275