| 2006 |
VARP (Varp/ANKRD27) functions as a guanine nucleotide exchange factor (GEF) for Rab21, preferentially binding GDP-bound Rab21 and catalyzing nucleotide exchange. Both the VPS9 domain and ankyrin repeats are required for endosomal localization and in vivo GEF activity. Ectopic expression causes enlargement of early endosomes and giant late endosomes. |
In vitro GEF assay, RNAi knockdown, subcellular localization by fluorescence microscopy, deletion/domain analysis |
Journal of cell science |
High |
16525121
|
| 2008 |
VARP physically interacts with active GTP-bound Rab38 via its ankyrin repeat 1 (ANK1) domain, functioning as a Rab38 effector. VARP is recruited to Rab38-positive organelles in an ANK1-dependent manner. |
Yeast two-hybrid screen, co-immunoprecipitation, in vitro pulldown with GTP/GDP-locked Rab38, fluorescence colocalization |
Biochemical and biophysical research communications |
Medium |
18477474
|
| 2009 |
VARP is a specific Rab32/38 effector; its first ankyrin repeat (ANKR1) domain functions as a GTP-dependent Rab32/38-binding domain. siRNA-mediated knockdown of Varp in melan-a melanocytes causes dramatic reduction of Tyrp1 (tyrosinase-related protein 1) signals from melanosomes without affecting Pmel17, demonstrating a role in melanogenic enzyme trafficking. |
Yeast two-hybrid, siRNA knockdown, deletion/domain analysis, immunofluorescence microscopy |
Molecular biology of the cell |
High |
19403694
|
| 2009 |
VARP interacts with TI-VAMP/VAMP7 through a specific interacting domain (ID). VARP, TI-VAMP, and Rab21 co-localize in perinuclear regions and transport vesicles in differentiating hippocampal neurons. Silencing Varp by RNAi, or expressing the ID domain or a Varp form lacking its VPS9 domain, impairs neurite growth, establishing VARP as a positive regulator of neurite growth via both its GEF activity and VAMP7 interaction. |
Co-immunoprecipitation, RNAi knockdown, domain expression, fluorescence colocalization in hippocampal neurons |
EMBO reports |
High |
19745841
|
| 2010 |
Ala-based site-directed mutagenesis identified critical residues for Rab32/38–VARP complex formation: Val-92 in Rab32 switch II (Val-78 in Rab38) is required for VARP binding, and Gln-509 and Tyr-550 in the ANKR1 domain of VARP are required for Rab32/38 binding. VARP point mutants Q509A and Y550A do not support peripheral melanosomal distribution of Tyrp1. The VPS9 domain GEF activity is dispensable for Tyrp1 trafficking, whereas VAMP7-binding ability is required. |
Site-directed mutagenesis, co-immunoprecipitation, knockdown-rescue experiments, immunofluorescence |
The Journal of biological chemistry |
High |
21187289
|
| 2011 |
Knockdown-rescue experiments in melanocytes showed that the Rab21-GEF activity of VARP (via its VPS9 domain) is required for forskolin-induced dendrite formation, whereas the Rab32/38 effector function (ANKR1) is not. Conversely, the Rab32/38 effector function is required for Tyrp1 transport to melanosomes, not dendrite formation. VAMP7-binding ability is required for both functions. |
siRNA knockdown, rescue with point mutants (VPS9 D310A/Y350A, ANKR1 Q509A/Y550A, VAMP7-binding deficient), morphological readout |
Molecular biology of the cell |
High |
22171327
|
| 2012 |
Crystal structure of the second ankyrin repeat domain of VARP in complex with the cytosolic portion of VAMP7 reveals that the VAMP7 SNARE motif is trapped between VARP and the VAMP7 longin domain. VARP kinetically inhibits VAMP7 SNARE complex formation, trapping it in a closed, fusogenically inactive conformation. This inhibition is enhanced when VARP simultaneously binds Rab32-GTP on the same membrane. |
X-ray crystallography, SNARE complex formation assay (in vitro), fluorescence colocalization, binding assays |
Nature structural & molecular biology |
High |
23104059
|
| 2014 |
VARP is recruited to endosomal membranes via direct interaction with VPS29, a subunit of the retromer complex; this recruitment is independent of Rab32 binding. The VARP ankyrin repeat/Rab32:GTP complex structure was determined. Transport of GLUT1 from endosomes to the cell surface requires VARP, VPS29, and VAMP7 and depends on the direct VPS29–VARP interaction. Endocytic cycling of VAMP7 depends on its interaction with VARP and consequently on retromer. |
X-ray crystallography (VARP ankyrin repeat/Rab32:GTP), direct pulldown, co-immunoprecipitation, siRNA knockdown of VARP/VPS29/VAMP7 with GLUT1 trafficking readout |
Developmental cell |
High |
24856514
|
| 2015 |
Rab40C, an atypical Rab containing a SOCS box that recruits a ubiquitin ligase complex, binds the ANKR2 domain of VARP and promotes its proteasomal degradation. Overexpression of Rab40C reduces Tyrp1 signals by degrading VARP; knockdown of Rab40C increases VARP levels. This identifies Rab40C as a regulator of Tyrp1 trafficking via controlling VARP protein stability. |
Co-immunoprecipitation, domain mapping, overexpression and knockdown, proteasome inhibitor experiments, immunofluorescence |
Biology open |
Medium |
25661869
|
| 2016 |
RACK1 binds the VARP ANKR2 domain and competes with Rab40C for the same binding site, thereby stabilizing VARP protein levels. Knockdown of RACK1 reduces Varp protein level and inhibits dendrite outgrowth in melanocytes; RACK1 overexpression inhibits the Varp–Rab40C interaction and counteracts negative effects of Rab40C on dendrite outgrowth. |
Co-immunoprecipitation, siRNA knockdown, overexpression, competitive binding assay, morphological readout |
The Journal of investigative dermatology |
Medium |
27066885
|
| 2018 |
VARP interacts with VAMP7 and kinesin 1, controls the peripheral pool of VAMP7-containing secretory lysosomes, and regulates cellular response to substrate rigidity. LRRK1 and VARP interact with VAMP7 in a competitive manner; LRRK1 negatively regulates VAMP7-mediated exocytosis while VARP promotes it, constituting a tug-of-war mechanism governing biomechanical control of lysosomal secretion. |
Co-immunoprecipitation, siRNA knockdown, atomic force microscopy, fluorescence microscopy of vesicle pools |
iScience |
Medium |
30240735
|
| 2020 |
NMR/X-ray structural determination of the complex between retromer subunit VPS29 and a 12-residue, four-cysteine/Zn++ microdomain (termed a Zn-fingernail) present in VARP. Mutations abolishing VPS29–VARP binding inhibit trafficking from endosomes to the cell surface. VARP and TBC1D5 bind the same site on VPS29 and compete for VPS29 binding in vivo. Structural analysis indicates VARP preferentially binds assembled retromer coats by simultaneously engaging two VPS29 subunits. |
NMR spectroscopy, X-ray crystallography, mutagenesis, co-immunoprecipitation competition assay, trafficking assay |
Nature communications |
High |
33024112
|
| 2020 |
VARP and Rab9 are dispensable for Rab32-mediated killing of Salmonella Typhi in macrophages (BRAM pathway). shRNA knockdown of VARP in macrophages did not affect Rab32 recruitment to Salmonella-containing vacuoles (SCV) or bacterial killing. |
shRNA knockdown, immunofluorescence of SCV, bacterial survival assay |
Frontiers in cellular and infection microbiology |
Medium |
33392103
|
| 2025 |
VARP directly interacts with SNX27 (identified biochemically and by AlphaFold modeling). In a fully reconstituted system with purified proteins and membranes, VARP is required to assemble a proposed endosomal supercomplex comprising SNX27, ESCPE-1 (SNX2/SNX6), and Retromer in vitro. VARP co-immunoprecipitates all coat components in cells. This places VARP as a scaffold for metazoan endosomal coat supercomplex assembly. |
Biochemical reconstitution with purified proteins, liposome tubulation assay, AlphaFold structural modeling, co-immunoprecipitation |
Science advances |
High |
39937906
|
| 2025 |
Knockout of VARP inhibits starvation-induced autophagic ATP secretion (amphisome pathway). RAB21 overexpression rescues ATP secretion in RAB21 KO cells but not in VARP KO cells, placing VARP downstream or in parallel to RAB21 in this secretory pathway. VARP partially colocalizes with LC3 upon starvation. |
CRISPR/KO of VAMP7/RAB21/VARP, ATP release assay, rescue overexpression, fluorescence colocalization |
Autophagy reports |
Medium |
40395984
|