SNX20

SNX20 (SLIC-1) is an endosomal sorting nexin that controls the subcellular trafficking of the leukocyte adhesion receptor PSGL-1 (PMID:18196517). It binds directly to the cytoplasmic domain of PSGL-1 through a mapped interaction motif (PMID:18196517), and its Phox homology (PX) domain binds phosphoinositides to target the resulting PSGL-1/SNX20 complex to endosomes (PMID:18196517). Loss of the murine homologue does not impair PSGL-1-dependent signaling or neutrophil adhesion, indicating that SNX20 acts in endosomal recycling/sorting of PSGL-1 rather than in outside-in signaling or leukocyte recruitment (PMID:18196517). Beyond this PSGL-1 trafficking role, no further binding partners or mechanistic detail for SNX20 have been characterized in the available corpus (PMID:30072438).

1. 2008 Medium

   Establishing a physical partner for SNX20 defined its first molecular function: a yeast two-hybrid screen identified direct binding to the cytoplasmic domain of the adhesion receptor PSGL-1.

   Evidence Yeast two-hybrid screen, reciprocal co-immunoprecipitation, and motif mapping

   PMID:18196517

   Open questions at the time

   • Binding interface defined only by motif mapping, not by structure
   • Whether SNX20 binds other receptor tails was not tested
2. 2008 Medium

   Localizing the complex addressed where SNX20 acts: its PX domain binds phosphoinositides and targets the PSGL-1/SNX20 complex to endosomes, placing SNX20 in the membrane sorting machinery.

   Evidence Colocalization imaging and subcellular fractionation

   PMID:18196517

   Open questions at the time

   • Specific phosphoinositide species bound not resolved
   • No direct lipid-binding biochemistry reported
3. 2008 Medium

   A knockout addressed whether SNX20 contributes to PSGL-1 signaling versus trafficking: loss of the murine homologue left PSGL-1-dependent signaling and neutrophil adhesion intact, confining SNX20's role to endosomal sorting rather than leukocyte recruitment.

   Evidence Knockout mouse with neutrophil adhesion and signaling assays

   PMID:18196517

   Open questions at the time

   • Direct measurement of PSGL-1 endosomal cycling kinetics not shown
   • Possible redundancy with related sorting nexins not assessed
4. 2018 Low

   Domain analysis placed SNX20 in the SNX-PXB family of predicted endosome-associated scaffolds, but no SNX20-specific interactome was generated.

   Evidence Quantitative proteomics on SNX21 with domain-based classification of SNX20

   PMID:30072438

   Open questions at the time

   • No direct experiment performed on SNX20 in this study
   • SNX20 binding partners beyond PSGL-1 remain unidentified
   • Scaffold function is predicted, not demonstrated

• Whether SNX20 has cargoes or functions beyond PSGL-1, and the molecular consequences of its endosomal sorting activity, remain undefined.
• No SNX20-specific interactome
• No structural model of the PX or PXB domains
• Functional significance of PSGL-1 recycling not established