Fig. 8: Overlaid viral cytochrome b5 structures showing the positioning of the conserved histidine residues (red) binding the heme.
From: Cytochrome b5 occurrence in giant and other viruses belonging to the phylum Nucleocytoviricota
Note that there is some variability in the heme-adjacent residues. Human, amoeba, and virus conserved F40 (alignment position 91) is a tyrosine in faunusvirus, while F63 (alignment position 114) is a conserved methionine in mimivirus, megavirus, tupanvirus, and moumouvirus, but a phenylalanine in soil faunusvirus, hyperion virus, terrestrivirus and metazoan cytochrome b5s.
