Comparative cellular processing of the human immunodeficiency virus (HIV-1) envelope glycoprotein gp160 by the mammalian subtilisin/kexin-like convertases

We present here the pulse and pulse-chase analysis of the biosynthesis of the envelope glycoprotein gp160 and its intracellular processing by the subtilisin/kexin-like convertases furin, PACE4, PC1, PC2, PC5 and its isoform PC5/6-B. We demonstrate that furin and to a much lesser extent PACE4, PC5/6-B and PC1 are candidate enzymes capable of processing gp160 intracellularly. Furthermore we show that furin can also process gp 160/gp120 into gp77/gp53 products by cleavage at the sequence RIQR down arrow GPGR just preceding the conserved GPGR structure found at the tip of the hypervariable V3 loop. The results show that processing into gp120 could occur at or before the trans-Golgi network (TGN) where sulphation of the oligosaccharide moieties of gp160 was detected, In contrast, the formation of gp77/gp53 by furin is a late event occurring after exit from the TGN. Our data also revealed that the alpha-glucosidase I inhibitor N-butyldeoxynojirimycin, although affecting the oligosaccharide composition of gp 160, does not impair the processing of either gp160 or gp120 by either furin or PACE4. Finally, the co-expression of the [Arg(355), Arg(358)]-alpha-1-antitrypsin Portland variant was shown to potently inhibit the processing of both gp160 and gp120 by these convertases.