scholarly journals Robustness and innovation along the endocytic route: Lessons from darkness

2021 ◽  
Vol 220 (7) ◽  
Author(s):  
Kaela S. Singleton ◽  
Victor Faundez
Keyword(s):  
Membrane Protein ◽  
Membrane Traffic ◽  
Sorting Signals ◽  
Fail Safe

What mechanisms ensure the loading of a SNARE into a nascent carrier? In this issue, Bowman et al. (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202005173) describe an unprecedented mechanism where two sorting complexes, AP-3 and BLOC-1, the latter bound to syntaxin 13, work as a fail-safe to recognize sorting signals in VAMP7, a membrane protein required for fusion to melanosomes. Their observations define one of the first examples of distributed robustness in membrane traffic mechanisms.

scholarly journals Jagunal is required for reorganizing the endoplasmic reticulum during Drosophila oogenesis

2007 ◽  
Vol 176 (7) ◽  
pp. 941-952 ◽  
Author(s):  
Sangil Lee ◽  
Lynn Cooley
Keyword(s):  
Endoplasmic Reticulum ◽  
Drosophila Melanogaster ◽  
Membrane Protein ◽  
Membrane Traffic ◽  
Protein Loss ◽  
Drosophila Oogenesis ◽  
Vesicular Traffic ◽  
Lateral Membrane ◽  
Evolutionarily Conserved ◽  
Er Membrane

Vesicular traffic in the Drosophila melanogaster oocyte occurs actively during vitellogenesis. Although endocytosis in the oocyte has been well characterized, exocytic vesicular traffic is less well understood. We show that the oocyte endoplasmic reticulum (ER) becomes concentrated into subcortical clusters during vitellogenesis. This ER reorganization requires Jagunal, which is an evolutionarily conserved ER membrane protein. Loss of Jagunal reduces vesicular traffic to the oocyte lateral membrane, but does not affect posterior polarized vesicular traffic, suggesting a role for Jagunal in facilitating vesicular traffic in the subcortex. Reduced membrane traffic caused by loss of Jagunal affects oocyte and bristle growth. We propose that ER reorganization is an important mechanism used by cells to prepare for an increased demand for membrane traffic, and Jagunal facilitates this process through ER clustering.

scholarly journals Phosphorylation of the AP2 μ subunit by AAK1 mediates high affinity binding to membrane protein sorting signals

2002 ◽  
Vol 156 (5) ◽  
pp. 791-795 ◽  
Author(s):  
Doris Ricotta ◽  
Sean D. Conner ◽  
Sandra L. Schmid ◽  
Kurt von Figura ◽  
Stefan Höning
Keyword(s):  
Membrane Proteins ◽  
Membrane Protein ◽  
Affinity Binding ◽  
Β Subunit ◽  
High Affinity Binding ◽  
Threonine Residue ◽  
Receptor Mediated Endocytosis ◽  
High Affinity ◽  
Sorting Signals

During receptor-mediated endocytosis, AP2 complexes act as a bridge between the cargo membrane proteins and the clathrin coat by binding to sorting signals via the μ2 subunit and to clathrin via the β subunit. Here we show that binding of AP2 to sorting signals in vitro is regulated by phosphorylation of the μ2 subunit of AP2. Phosphorylation of μ2 enhances the binding affinity of AP2 for sorting motifs as much as 25-fold compared with dephosphorylated AP2. The recognition of sorting signals was not affected by the phosphorylation status of the α or β2 subunit, suggesting that phosphorylation of μ2 is critical for regulation of AP2 binding to sorting signals. Phosphorylation of μ2 occurs at a single threonine residue (Thr-156) and is mediated by the newly discovered adaptor-associated kinase, AAK1, which copurifies with AP2. We propose that phosphorylation of the AP2 μ2 subunit by AAK1 ensures high affinity binding of AP2 to sorting signals of cargo membrane proteins during the initial steps of receptor-mediated endocytosis.

scholarly journals Tyrosine-based Membrane Protein Sorting Signals Are Differentially Interpreted by Polarized Madin-Darby Canine Kidney and LLC-PK1Epithelial Cells

1998 ◽  
Vol 273 (41) ◽  
pp. 26862-26869 ◽  
Author(s):  
Denise L. Roush ◽  
Cara J. Gottardi ◽  
Hussein Y. Naim ◽  
Michael G. Roth ◽  
Michael J. Caplan
Keyword(s):  
Membrane Protein ◽  
Protein Sorting ◽  
Madin Darby Canine Kidney ◽  
Sorting Signals ◽  
Darby Canine Kidney ◽  
Canine Kidney

TMCC3 localizes at the three-way junctions for the proper tubular network of the endoplasmic reticulum

2019 ◽  
Vol 476 (21) ◽  
pp. 3241-3260
Author(s):  
Sindhu Wisesa ◽  
Yasunori Yamamoto ◽  
Toshiaki Sakisaka
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Mammalian Cells ◽  
Coiled Coil ◽  
Transmembrane Domains ◽  
Domain Family ◽  
Coiled Coil Domain ◽  
U2os Cells ◽  
Er Membrane

The tubular network of the endoplasmic reticulum (ER) is formed by connecting ER tubules through three-way junctions. Two classes of the conserved ER membrane proteins, atlastins and lunapark, have been shown to reside at the three-way junctions so far and be involved in the generation and stabilization of the three-way junctions. In this study, we report TMCC3 (transmembrane and coiled-coil domain family 3), a member of the TEX28 family, as another ER membrane protein that resides at the three-way junctions in mammalian cells. When the TEX28 family members were transfected into U2OS cells, TMCC3 specifically localized at the three-way junctions in the peripheral ER. TMCC3 bound to atlastins through the C-terminal transmembrane domains. A TMCC3 mutant lacking the N-terminal coiled-coil domain abolished localization to the three-way junctions, suggesting that TMCC3 localized independently of binding to atlastins. TMCC3 knockdown caused a decrease in the number of three-way junctions and expansion of ER sheets, leading to a reduction of the tubular ER network in U2OS cells. The TMCC3 knockdown phenotype was partially rescued by the overexpression of atlastin-2, suggesting that TMCC3 knockdown would decrease the activity of atlastins. These results indicate that TMCC3 localizes at the three-way junctions for the proper tubular ER network.

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