Interchangeable but essential functions of SNX1 and SNX2 in the association of retromer with endosomes and the trafficking of mannose 6-phosphate receptors.
The retromer is a cytosolic/peripheral membrane protein complex that mediates the retrieval of the cation-independent mannose 6-phosphate receptor from endosomes to the trans-Golgi network (TGN) in mammalian cells. Previous studies showed that the mammalian retromer comprises three proteins, named Vps26, Vps29, and Vps35, plus the sorting nexin, SNX1. There is conflicting evidence, however, as to whether a homologous sorting nexin, SNX2, is truly a component of the retromer. In addition, the nature of the subunit interactions and assembly of the mammalian retromer complex are poorly understood. We have addressed these issues by performing biochemical and functional analyses of endogenous retromers in the human cell line HeLa. We found that the mammalian retromer complex consists of two autonomously assembling subcomplexes, namely, a Vps26-Vps29-Vps35 obligate heterotrimer and a SNX1/2 alternative heterodimer or homodimer. The association of Vps26-Vps29-Vps35 with endosomes requires the presence of either SNX1 or SNX2, whereas SNX1/2 can be recruited to endosomes independently of Vps26-Vps29-Vps35. We also found that the presence of either SNX1 or SNX2 is essential for the retrieval of the cation-independent mannose 6-phosphate receptor to the TGN. These observations indicate that the mammalian retromer complex assembles by sequential association of SNX1/2 and Vps26-Vps29-Vps35 subcomplexes on endosomal membranes and that SNX1 and SNX2 play interchangeable but essential roles in retromer structure and function.
Rojas
Raul
R
Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, Building 18T/Room 101, National Institutes of Health, Bethesda, MD 20892, USA.
Kametaka
Satoshi
S
Haft
Carol R
CR
Bonifacino
Juan S
JS
D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D002850:Chromatography, Gel; D019281:Dimerization; D011992:Endosomes / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D046912:Multiprotein Complexes / Q000378:metabolism; D011485:Protein Binding; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D021381:Protein Transport; D017527:Receptor, IGF Type 2 / Q000378:metabolism*; D058305:Sorting Nexins; D020798:Two-Hybrid System Techniques; D033921:Vesicular Transport Proteins / Q000737:chemistry / Q000378:metabolism*
D002352:Carrier Proteins; D046912:Multiprotein Complexes; D021122:Protein Subunits; D017527:Receptor, IGF Type 2; C513978:SNX1 protein, human; C513979:SNX2 protein, human; D058305:Sorting Nexins; C498296:VPS26A protein, human; C419572:VPS29 protein, human; C419573:VPS35 protein, human; D033921:Vesicular Transport Proteins