Endogenous envelope proteins originate from retroviral envelope proteins, which mediate receptor recognition and membrane fusion during early infection. Endogenous envelope proteins may have kept, lost or modified their original function during evolution.
Subcellular locations: Cell membrane
This uncleaved form present at the cell surface represents the major form .
Subcellular locations: Secreted
This secreted form, which is released in the extracellular medium following cleavage, constitutes a minor form .
Expressed at high level in the placenta and stem cells (at protein level) . Also expressed in the kidney but at a lower level . Endogenous retroviral envelope protein HEMO, secreted form: Present in the blood of pregnant women (at protein level) .