Figure 9. Hypothetical model of p17 secretion from Gag-expressing cells.

The cytosolic Pr55^Gag, a polyprotein composed of the matrix protein p17 − whose NH₂-terminal myristic acid moiety in its sequestered conformation is in light green −, the capsid protein p24, the nucleocapsid protein p7, and the p6 domains (1), is recruited to the cellular membrane by PI(4,5)P₂, according to the model proposed by Saad et al.²⁶ (2). PI(4,5)P₂ association with the p17 highly basic domain induces a conformational change enabling the membrane-embedded aspartyl-protease to cleave p17 from the polyprotein Pr55^Gag (3). As a Pr55^Gag-free protein, p17 then moves to the extracellular space through an unconventional secretion mechanism (4).