SNX1

SNX1 is a sorting nexin that governs the sorting of internalized membrane cargo between endosome-to-Golgi retrieval, plasma membrane recycling, and degradative pathways (PMID:17101778, PMID:18088323). Its core conserved function, established through the yeast ortholog Vps5p, is retrieval of cargo from the endosomal/prevacuolar compartment back to the late Golgi (PMID:9175702), and in mammals SNX1 acts as one half of an interchangeable SNX1/SNX2 dimer that, together with the obligate Vps26-Vps29-Vps35 trimer, constitutes the retromer complex; either SNX1 or SNX2 is required to recruit the trimer to endosomes and to retrieve CI-MPR and sortilin to the TGN (PMID:17101778, PMID:18088323). Structurally, SNX1 assembles into helical rows of crosslinked dimers wrapped around tubular membranes, providing the membrane-deforming activity that generates endosome-to-TGN transport carriers (PMID:33658379), and these carriers mediate retrograde transport of cargo including Shiga toxin (PMID:17498660). Beyond retrieval, SNX1 binds the cytoplasmic tails of multiple cargoes — the EGFR lysosomal targeting motif (PMID:8638121), at least ten GPCR tails with nanomolar affinity (PMID:15452121) — and can direct receptors to degradation: it is required for retromer-independent lysosomal sorting of activated PAR1 (PMID:16407403) and for proteasomal turnover of AT1R (PMID:33972750), while conversely retrieving E-cadherin from a degradative route to promote its recycling (PMID:17502486). SNX1 also opposes ESCRT-0 (Hrs/HGRS-1) degradative microdomain assembly on endosomes in conjunction with RME-8 (PMID:28053230), links to plasma-membrane recycling via a direct DxF-motif interaction with the SNX27 FERM domain (PMID:34866035), and during starvation cooperates with SNX2 to form endosomal tubules that tether to VAPB-positive ER subdomains supporting autophagosome biogenesis (PMID:36585258).

1. 1996 Medium

   Established SNX1 as a cargo-tail-binding protein that controls receptor fate, by showing it engages the EGFR lysosomal targeting code and promotes receptor degradation.

   Evidence Co-IP/binding assay and overexpression measuring EGFR surface levels and degradation rates

   PMID:8638121

   Open questions at the time

   • Based on overexpression rather than endogenous loss-of-function
   • Did not define the endosomal machinery or membrane mechanism downstream of cargo binding
2. 1997 High

   Defined the conserved core function of the SNX1 ortholog as endosome-to-late-Golgi retrieval, framing SNX1 as a retrieval factor rather than purely a degradative router.

   Evidence Yeast Vps5p null mutant analysis with fractionation, immunofluorescence, and vacuolar sorting assays

   PMID:9175702

   Open questions at the time

   • Established in yeast ortholog; mammalian cargo set not yet defined
   • Did not identify partner subunits of the retrieval machinery
3. 2004 Medium

   Showed SNX1 binds a broad set of GPCR C-terminal tails with high affinity, generalizing its cargo-recognition role beyond EGFR to seven-transmembrane receptors.

   Evidence GST pull-down across 59 GPCR tail fusions, SPR kinetics, and NK1 receptor truncation mapping

   PMID:15452121

   Open questions at the time

   • In vitro binding did not establish trafficking outcome for each receptor
   • Did not resolve which interactions retrieve versus degrade cargo
4. 2006 High

   Resolved the architecture of mammalian retromer as a SNX1/SNX2 dimer plus a Vps26-Vps29-Vps35 trimer and established that SNX1/SNX2 recruits the trimer to endosomes for CI-MPR retrieval.

   Evidence Biochemical fractionation, reciprocal Co-IP, and combinatorial siRNA depletion with CI-MPR trafficking assays in HeLa cells

   PMID:17101778

   Open questions at the time

   • Did not determine how the SNX dimer is itself targeted to the correct membrane microdomain
   • Interchangeability of SNX1 vs SNX2 for all cargoes not exhaustively tested
5. 2006 High

   Demonstrated a retromer-independent degradative role for SNX1, showing endogenous SNX1 routes activated PAR1 to lysosomes without Vps26/Vps35, Hrs, or Tsg101.

   Evidence siRNA depletion with siRNA-resistant rescue and epistasis knockdowns plus agonist-induced PAR1 degradation assays

   PMID:16407403

   Open questions at the time

   • Molecular machinery substituting for retromer/ESCRT in this pathway not identified
   • Generality of retromer-independent degradation to other GPCRs unresolved
6. 2007 High

   Defined SNX1-positive endosome-to-TGN transport carriers as discrete structures and broadened the retrieval cargo repertoire while also showing SNX1 can rescue cargo from degradation toward recycling.

   Evidence Quantitative immuno-EM and 3D electron tomography (sortilin/MPR carriers); siRNA with E-cadherin recycling/degradation assays; Shiga toxin transport assays

   PMID:17498660 PMID:17502486 PMID:18088323

   Open questions at the time

   • Did not establish how cargo is selected into versus excluded from a given carrier
   • Redundancy with SNX2 left some functions only partially attributable to SNX1
7. 2007 Medium

   Identified EHD1 as a factor stabilizing SNX1 endosomal tubules, linking tubule integrity to retromer-dependent CI-MPR retrieval.

   Evidence Comparative endosomal proteomics, Co-IP, EHD1 RNAi, and dominant-negative P-loop mutant with CI-MPR trafficking assay

   PMID:17868075

   Open questions at the time

   • Direct versus indirect EHD1-SNX1 contact not established
   • Did not resolve the mechanical step EHD1 contributes to tubule stability
8. 2017 High

   Revealed a regulatory role for SNX1 in restricting degradative microdomains, showing SNX1/SNX-1 with RME-8 opposes ESCRT-0 (Hrs/HGRS-1) assembly on endosomes.

   Evidence C. elegans snx-1 null and rme-8 ts mutants with live imaging and membrane fractionation, confirmed by SNX1/SNX2 siRNA in HeLa cells

   PMID:28053230

   Open questions at the time

   • Mechanism by which SNX1/RME-8 displaces or excludes HGRS-1 not defined
   • Relationship of this activity to retromer-mediated retrieval not fully mapped
9. 2018 Medium

   Established the biochemical basis of a SNX1-containing BAR-domain heterodimer by reconstituting a stable 1:1 SNX1-SNX6 complex.

   Evidence Recombinant co-expression and purification with solution stoichiometry determination

   PMID:29908913

   Open questions at the time

   • Functional consequences of the SNX1-SNX6 pairing not tested
   • Relationship to the SNX1/SNX2 dimer not resolved
10. 2021 High

    Provided the structural mechanism of membrane deformation, showing SNX1 forms crosslinked helical lattices of dimers around tubular membranes and how retromer reorganizes this coat.

    Evidence Cryo-EM of SNX1 on tubular membranes with comparison to the retromer-SNX coat

    PMID:33658379

    Open questions at the time

    • Did not capture cargo within the lattice
    • Dynamics of coat assembly and disassembly in cells not resolved
11. 2021 High

    Connected SNX1 to plasma-membrane recycling machinery by mapping a direct DxF-motif interaction between the SNX1 N-terminus and the SNX27 FERM domain.

    Evidence Purified-protein pulldowns, ITC affinity measurement, and DxF/N-terminal mutagenesis abolishing binding

    PMID:34866035

    Open questions at the time

    • Cellular cargo handed off via this interface not defined here
    • Modest ~10 uM affinity leaves regulation of the interaction open
12. 2021 Medium

    Extended SNX1's degradative routing to proteasomal control of a GPCR, showing SNX1 loss raises AT1R levels and calcium signaling by reducing AT1R ubiquitination and proteasomal turnover.

    Evidence CRISPR KO mice and siRNA in A10 cells with Co-IP, cycloheximide chase, and proteasomal/lysosomal inhibitor experiments

    PMID:33972750

    Open questions at the time

    • Mechanistic link between an endosomal sorting nexin and proteasomal degradation not resolved
    • Whether SNX1 acts directly or via an adaptor on AT1R unclear
13. 2022 Medium

    Implicated SNX1 in autophagy initiation, showing starvation-induced SNX1 tubules tether to VAPB-positive ER subdomains in cooperation with SNX2 to support autophagosome biogenesis.

    Evidence SNX1/SNX2 depletion with live-cell imaging of endosomal tubules and ER autophagy markers plus autophagic response assays

    PMID:36585258

    Open questions at the time

    • Direct SNX1 contribution distinct from SNX2-VAPB binding not isolated
    • How tubule-ER contact promotes autophagosome formation mechanistically not defined
14. 2024 Medium

    Identified chaperone and disease-relevant regulation of SNX1, showing DNAJC13/Hsc70 controls SNX1 association in retromer transport and that excess alpha-synuclein weakens SNX1-VPS35 coupling.

    Evidence Co-IP of DNAJC13-SNX1-Hsc70, Hsc70 inhibition, and alpha-synuclein overexpression with SNX1-VPS35 interaction and retrograde transport assays in PD-mimetic models

    PMID:38886344

    Open questions at the time

    • Causal contribution to disease pathology not established
    • Whether alpha-synuclein acts directly on the SNX1-VPS35 interface unresolved

• How SNX1 discriminates among retrieval, recycling, and degradative fates for a given bound cargo, and what signals switch it between these outputs, remains unresolved.
• No unifying model linking cargo-tail recognition to fate selection
• Regulatory inputs (post-translational modification, lipid signals) that direct SNX1 between pathways not defined