Cytochrome c oxidase subunit IIa family
This family consists of the cytochrome c oxidase subunit IIa family. The bax-type cytochrome c oxidase from Thermus thermophilus is known as a two subunit enzyme. From its crystal structure, it was discovered that an additional transmembrane helix 'subunit IIa' spans the membrane. This subunit consists of 34 residues forming one helix across the membrane. The presence of this subunit seems to be important for the function of cytochrome c oxidases.
Jiyao W et al.(2023). "The conserved domain database in 2023.",