S-Palmitoylation determines TMEM55B-dependent positioning of lysosomes.

The spatio-temporal cellular distribution of lysosomes depends on active transport mainly driven by microtubule-motors such as kinesins and dynein. Different protein complexes attach these molecular motors to their vesicular cargo: TMEM55B, as an integral lysosomal membrane protein, is a component of such a complex mediating the retrograde transport of lysosomes by establishing an interaction with the cytosolic scaffold protein JIP4 and dynein/dynactin. Here we show that TMEM55B and its paralog TMEM55A are S-palmitoylated proteins and lipidated at multiple cysteine-residues. Mutation of all cysteines in TMEM55B prevents S-palmitoylation and causes the retention of the mutated protein in the Golgi-apparatus. Consequently, non-palmitoylated TMEM55B is no longer able to modulate lysosomal positioning and the perinuclear clustering of lysosomes. Additional mutagenesis of the dileucine-based lysosomal sorting motif in non-palmitoylated TMEM55B leads to partial missorting to the plasma membrane instead of retention in the Golgi, implicating a direct effect of S-palmitoylation on the adaptor-protein-dependent sorting of TMEM55B. Our data suggest a critical role of S-palmitoylation on the trafficking of TMEM55B and TMEM55B-dependent lysosomal positioning.