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Mol Biol Cell. 2008 Apr;19(4):1415-26. doi: 10.1091/mbc.E07-12-1239. Epub 2008 Feb 6.

Phosphatidylinositol-4-kinase type II alpha contains an AP-3-sorting motif and a kinase domain that are both required for endosome traffic.

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  • 1Graduate Program in Biochemistry, Cell, and Developmental Biology, Emory University, Atlanta, GA 30322, USA.


The adaptor complex 3 (AP-3) targets membrane proteins from endosomes to lysosomes, lysosome-related organelles and synaptic vesicles. Phosphatidylinositol-4-kinase type II alpha (PI4KIIalpha) is one of several proteins possessing catalytic domains that regulate AP-3-dependent sorting. Here we present evidence that PI4KIIalpha uniquely behaves both as a membrane protein cargo as well as an enzymatic regulator of adaptor function. In fact, AP-3 and PI4KIIalpha form a complex that requires a dileucine-sorting motif present in PI4KIIalpha. Mutagenesis of either the PI4KIIalpha-sorting motif or its kinase-active site indicates that both are necessary to interact with AP-3 and properly localize PI4KIIalpha to LAMP-1-positive endosomes. Similarly, both the kinase activity and the sorting signal present in PI4KIIalpha are necessary to rescue endosomal PI4KIIalpha 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.

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