Howard Hughes Medical Institute and Department of Molecular and Cell Biology, University of California at Berkeley, CA 94720, USA-
Abstract: The phosphoinositide-binding proteins Ent3p and Ent5p are required for protein transport from the trans-Golgi network -TGN- to the vacuole in Saccharomyces cerevisiae- Both proteins interact with the monomeric clathrin adaptor Gga2p, but Ent5p also interacts with the clathrin adaptor protein 1 -AP-1- complex, which facilitates retention of proteins such as Chs3p at the TGN- When both ENT3 and ENT5 are mutated, Chs3p is diverted from an intracellular reservoir to the cell surface- However, Ent3p and Ent5p are not required for the function of AP-1, but rather they seem to act in parallel with AP-1 to retain proteins such as Chs3p at the TGN- They have all the properties of clathrin adaptors, because they can both bind to clathrin and to cargo proteins- Like AP-1, Ent5p binds to Chs3p, whereas Ent3p facilitates the interaction between Gga2p and the endosomal syntaxin Pep12p- Thus, Ent3p has an additional function in Gga-dependent transport to the late endosome- Ent3p also facilitates the association between Gga2p and clathrin; however, Ent5p can partially substitute for this function- We conclude that the clathrin adaptors AP-1, Ent3p, Ent5p, and the Ggas cooperate in different ways to sort proteins between the TGN and the endosomes-