title: SNX18 is an SNX9 paralog that acts as a membrane tubulator in AP-1-positive endosomal trafficking.
abstract: SNX9, SNX18 and SNX30 constitute a separate subfamily of PX-BAR-containing sorting nexin (SNX) proteins. We show here that most tissues express all three paralogs, and immunoprecipitation and immunofluorescence experiments demonstrated that the SNX9-family proteins act as individual entities in cells. Their SH3 domains displayed a high selectivity for dynamin 2, and the PX-BAR units had the capacity to tubulate membranes when expressed in HeLa cells. As previously described for the PX-BAR domain of SNX9 (SNX9-PX-BAR), purified SNX18-PX-BAR caused liposome tubulation in vitro and had a binding preference for PtdIns(4,5)P(2). However, contrary to SNX9, which primarily acts in clathrin-mediated endocytosis at the plasma membrane, endogenous SNX18 localized to AP-1- and PACS1-positive endosomal structures, which were devoid of clathrin and resistant to Brefeldin A. Moreover, a gamma-adaptin recognition motif was defined in a low-complexity region of SNX18, and a complex of endogenous SNX18 and AP-1 could be immunoprecipitated after Brefeldin A treatment. Overexpression of SNX18 sequestered AP-1 from peripheral endosomes and resulted in the formation of short SNX18-decorated tubes with distinct dynamin puncta. The results indicate that SNX9-family members make up discrete membrane-scission units together with dynamin, and suggest that SNX18 mediates budding of carriers for AP-1-positive endosomal trafficking.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden.
authors.forename: Karin
authors.initials: K
authors.lastname: Håberg
authors.forename: Richard
authors.initials: R
authors.lastname: Lundmark
authors.forename: Sven R
authors.initials: SR
authors.lastname: Carlsson
mesh_terms: D033961:Adaptor Protein Complex 1 / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D021961:Cell Membrane Structures / Q000378:metabolism* / Q000648:ultrastructure; D034285:Dynamin II / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid; D058305:Sorting Nexins; D033921:Vesicular Transport Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D033961:Adaptor Protein Complex 1; C491914:PACS1 protein, human; C530791:SNX18 protein, human; C400533:SNX9 protein, human; D058305:Sorting Nexins; D033921:Vesicular Transport Proteins; D034285:Dynamin II