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Phosphatidylinositol-4-Kinase Type II Alpha Contains an AP-3–sorting Motif and a Kinase Domain That Are Both Required for Endosome Traffic

By Branch Craige, Gloria Salazar and Victor Faundez


The adaptor complex 3 (AP-3) targets membrane proteins from endosomes to lysosomes, lysosome-related organelles and synaptic vesicles. Phosphatidylinositol-4-kinase type II � (PI4KII�) is one of several proteins possessing catalytic domains that regulate AP-3–dependent sorting. Here we present evidence that PI4KII � uniquely behaves both as a membrane protein cargo as well as an enzymatic regulator of adaptor function. In fact, AP-3 and PI4KII � form a complex that requires a dileucine-sorting motif present in PI4KII�. Mutagenesis of either the PI4KII�-sorting motif or its kinase-active site indicates that both are necessary to interact with AP-3 and properly localize PI4KII � to LAMP-1–positive endosomes. Similarly, both the kinase activity and the sorting signal present in PI4KII � are necessary to rescue endosomal PI4KII � siRNA-induced mutant phenotypes. We propose a mechanism whereby adaptors use canonical sorting motifs to selectively recruit a regulatory enzymatic activity to restricted membrane domains

Year: 2007
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