%0 Journal Article
%T Autoinhibition Mechanism for Phosphoinositide Binding by the Endosomal Trafficking Protein Tom1
%J -
%D 2019
%R https://doi.org/10.1016/j.bpj.2018.11.2007
%X In eukaryotes, the adaptor protein Tom1 plays an important role in transporting ubiquitinated proteins (cargo) targeted for their degradation at the early/late endosomal/lysosomal pathway. The protein trafficking function of Tom1 can be inhibited due to infection by Shigella nexfleri. This bacterium induces the production of phosphatidylinositol-5-phosphate [PtdIns(5)P] in the host, and high levels of this phosphoinositide are shown to cause accumulation of Tom1 onto signaling endosomes, delaying the host protein degradation process and, simultaneously, facilitating bacterial survival. Tom1 is modular with an N-terminal VHS domain, followed by a central GAT domain, and a C-terminal disordered domain. The VHS domain of Tom1 has been shown to be responsible of PtdIns(5)P binding. Unexpectedly, we found that full-length Tom1 does not bind the phosphoinositide, suggesting an intramolecular modulatory mechanism in Tom1 that control its subcellular localization. Through truncation of the protein at different sites, we found that a region adjacent to the VHS domain, that we termed the linker region, is responsible for autoinhibition of PtdIns(5)P binding. Moreover, a highly conserved region within this linker presents an acidic dileucine motif that, when absent, favors binding of Tom1 to PtdIns(5)P. NMR data indicates that the acidic dileucine motif directly binds the Tom1 VHS domain following a fast exchange regime. The acidic dileucine binding site in the VHS domain partially overlaps with that for PtdIns(5)P but not with that for ubiquitin. Molecular dynamic simulations show that Tom1 cycles between open and closed conformations, with the latter dominated by a direct interaction of the VHS domain with the downstream linker region. Overall, our studies suggest a novel role of acidic dileucine motifs, which regulate the subcellular localization of Tom1 by blocking its membrane interactions at resting PtdIns(5)P intracellular levels without affecting its cargo trafficking function
%U https://www.cell.com/biophysj/fulltext/S0006-3495(18)33272-7