PROTEIN-TRANSPORT FROM THE SECRETORY TO THE ENDOCYTIC PATHWAY IN MAMMALIAN-CELLS

The trans-Golgi network (TGN) is the last station of the secretory pat hway where soluble and membrane proteins are sorted for subsequent tra nsport to endocytic compartments. This pathway is primarily followed b y two distinct but related mannose 6-phosphate receptors which exhibit complementary functions in soluble lysosomal enzyme targeting. These transmembrane proteins and their bound ligands are packaged in transpo rt intermediates coated with clathrin and the AP-1 assembly complex. T heir segregation is determined by the interaction of tyrosine- and di- leucine-based sorting determinants present in their cytoplasmic domain s with AP-1. Other membrane proteins such as the lysosomal membrane gl ycoproteins or envelope glycoproteins of herpes viruses, which contain similar sorting signals, may also follow the same pathway. In this re view, we will summarize our current understanding of the molecular mec hanisms leading to membrane protein sorting in the TGN and the formati on of AP-1-coated transport intermediates. (C) 1998 Elsevier Science B .V. All rights reserved.