Mdm1/Snx13 is a novel ER-endolysosomal interorganelle tethering protein.
Although endolysosomal trafficking is well defined, how it is regulated and coordinates with cellular metabolism is unclear. To identify genes governing endolysosomal dynamics, we conducted a global fluorescence-based screen to reveal endomembrane effector genes. Screening implicated Phox (PX) domain-containing protein Mdm1 in endomembrane dynamics. Surprisingly, we demonstrate that Mdm1 is a novel interorganelle tethering protein that localizes to endoplasmic reticulum (ER)-vacuole/lysosome membrane contact sites (MCSs). We show that Mdm1 is ER anchored and contacts the vacuole surface in trans via its lipid-binding PX domain. Strikingly, overexpression of Mdm1 induced ER-vacuole hypertethering, underscoring its role as an interorganelle tether. We also show that Mdm1 and its paralogue Ydr179w-a (named Nvj3 in this study) localize to ER-vacuole MCSs independently of established tether Nvj1. Finally, we find that Mdm1 truncations analogous to neurological disease-associated SNX14 alleles fail to tether the ER and vacuole and perturb sphingolipid metabolism. Our work suggests that human Mdm1 homologues may play previously unappreciated roles in interorganelle communication and lipid metabolism.
Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390 Mike.Henne@utsouthwestern.edu sde26@cornell.edu.
W Mike
WM
Henne
Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853 Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853.
Lu
L
Zhu
Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853 Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853.
Zsolt
Z
Balogi
Medical Research Council Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, England, UK.
Christopher
C
Stefan
Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853.
Jeffrey A
JA
Pleiss
Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853 Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853 Mike.Henne@utsouthwestern.edu sde26@cornell.edu.
Scott D
SD
Emr
D001665:Binding Sites; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism*; D007381:Intermediate Filament Proteins / Q000737:chemistry / Q000502:physiology*; D008247:Lysosomes / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000502:physiology*; D013107:Sphingolipids / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism
D007381:Intermediate Filament Proteins; C075618:MDM1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D013107:Sphingolipids