Retroviral envelope proteins mediate receptor recognition and membrane fusion during early infection. Endogenous envelope proteins may have kept, lost or modified their original function during evolution. This endogenous envelope protein has lost its original fusogenic properties but has immunosuppressive properties in vivo. SU mediates receptor recognition. TM anchors the envelope heterodimer to the viral membrane through one transmembrane domain. The other hydrophobic domain, called fusion peptide, mediates fusion of the viral membrane with the target cell membrane (By similarity). The surface (SU) and transmembrane (TM) proteins form a heterodimer. SU and TM are attached by noncovalent interactions or by a labile interchain disulfide bond (By similarity). Low expression in skin and testis. No expression in several cell lines. Contains the CKS-17 immunosuppressive domain present in many retroviral envelope proteins. As a synthetic peptide, it inhibits immune function in vitro and in vivo (By similarity). Specific enzymatic cleavages in vivo yield the mature SU and TM proteins. The CXXC motif is highly conserved across a broad range of retroviral envelope proteins. It is thought to participate in the formation of a labile disulfide bond possibly with the CX6CC motif present in the transmembrane protein. Isomerization of the intersubunit disulfide bond to an SU intrachain disulfide bond is thought to occur upon receptor recognition in order to allow membrane fusion (By similarity). Envelope protein HERV-H19 and HERV-H/p62 are allelic variants of the same provirus. Ortholog in Pan troglodytes. HERV-H family subgenomic RNAs have been observed. This provirus is intergenic, the closest flanking genes being TAIP2 and GALNT3. Belongs to the gamma type-C retroviral envelope protein family. HERV class-I H env subfamily.