sm1 and sm2 are comprised of both RFAD-Hα and B/retroB, while sm3 is comprised of RFAD-Hα only. Each N-terminus (NH2) of RFAD-Hα, B, and retroB is linked to the C-terminus (COOH) of huHF subunit (huHFα or huHFβ). That is, in sm1, the C-terminus of native MMOB was linked to the C-terminus of huHFβ, while in sm2, the N-terminus of native MMOB was linked to the C-terminus of huHFβ. In RFAD-Hα, the N-terminus of Hα (Ala64 to Leu321 of native MMOHα) is linked to the C-terminus of RFAD (FAD-binding domain of native MMOR). H6 is inserted for Ni2+-affinity purification, and L in sm1 to sm3 represents a linker peptide (G3SG3TG3SG3). smδ is only RFAD-Hα without linking to the huHF subunit.
