Stepwise deletion of the HIV type I glycoprotein 41 N terminus leads to anincreasing export of microvesicles containing uncleaved env glycoprotein

Deletion of two or more amino acid residues from the N terminus of HIV-1 gp 41 leads to an increasing loss of cleavability of the envelope (Env) precur sor on introduction of an env-expressing vector into HeLa-T4(+) cells. In p rotein analysis, this is paralleled by the appearance of a second form of u ncleaved Env precursor that is terminally sialylated. Cell-derived microves icles that preferentially incorporate this form of Env precursor were found in the culture medium. The same applies to a mutant with a nonfunctional c leavage site, indicating that a pathway by which uncleaved Env glycoprotein leaves the cell exists. The amount of exported glycoprotein is augmented a s compared with wild-type Env. Transfection with a wild-type Env-expressing vector leads to the presence of extracellular microvesicles that contain o nly the transmembrane domain of HIV-1 Env. Microvesicles derived from wild- type Env and mutant Env contain sialylated glycoproteins that are resistant to exo- and endoglycosidase treatment unless the particles have been previ ously lysed by detergent. This raises the possibility that the C-terminal d omains of the glycoproteins are exposed on the surface of the exported micr ovesicles.