Intracellular Targeting Signals and Lipid Specificity Determinants of the ALA/ALIS P 4 -ATPase Complex Reside in the Catalytic ALA α-Subunit

Members of the P 4 subfamily of P-type ATPases are believed to catalyze flipping of phospholipids across cellular membranes, in this way contributing to vesicle biogenesis in the secretory and endocytic pathways. P 4 -ATPases form heteromeric complexes with Cdc50-like proteins, and it has been suggested that these act as β-subunits in the P 4 -ATPase transport machinery. In this work, we investigated the role of Cdc50-like β-subunits of P 4 -ATPases for targeting and function of P 4 -ATPase catalytic α-subunits. We show that the Arabidopsis P 4 -ATPases ALA2 and ALA3 gain functionality when coexpressed with any of three different ALIS Cdc50-like β-subunits. However, the final cellular destination of P 4 -ATPases as well as their lipid substrate specificity are independent of the nature of the ALIS β-subunit they were allowed to interact with.