title: Structure and Membrane Binding Properties of the Endosomal Tetratricopeptide Repeat (TPR) Domain-containing Sorting Nexins SNX20 and SNX21.
abstract: Sorting nexins (SNX) orchestrate membrane trafficking and signaling events required for the proper distribution of proteins within the endosomal network. Their phox homology (PX) domain acts as a phosphoinositide (PI) recognition module that targets them to specific endocytic membrane domains. The modularity of SNX proteins confers a wide variety of functions from signaling to membrane deformation and cargo binding, and many SNXs are crucial modulators of endosome dynamics and are involved in a myriad of physiological and pathological processes such as neurodegenerative diseases, cancer, and inflammation. Here, we have studied the poorly characterized SNX20 and its paralogue SNX21, which contain an N-terminal PX domain and a C-terminal PX-associated B (PXB) domain of unknown function. The two proteins share similar PI-binding properties and are recruited to early endosomal compartments by their PX domain. The crystal structure of the SNX21 PXB domain reveals a tetratricopeptide repeat (TPR)-fold, a module that typically binds short peptide motifs, with three TPR α-helical repeats. However, the C-terminal capping helix adopts a highly unusual and potentially self-inhibitory topology. SAXS solution structures of SNX20 and SNX21 show that these proteins adopt a compact globular architecture, and membrane interaction analyses indicate the presence of overlapping PI-binding sites that may regulate their intracellular localization. This study provides the first structural analysis of this poorly characterized subfamily of SNX proteins, highlighting a likely role as endosome-associated scaffolds.
authors.affiliation: From the Institute for Molecular Bioscience, University of Queensland, St. Lucia, Queensland 4072, Australia.
authors.forename: Thomas
authors.initials: T
authors.lastname: Clairfeuille
authors.affiliation: From the Institute for Molecular Bioscience, University of Queensland, St. Lucia, Queensland 4072, Australia.
authors.forename: Suzanne J
authors.initials: SJ
authors.lastname: Norwood
authors.affiliation: From the Institute for Molecular Bioscience, University of Queensland, St. Lucia, Queensland 4072, Australia.
authors.forename: Xiaying
authors.initials: X
authors.lastname: Qi
authors.affiliation: From the Institute for Molecular Bioscience, University of Queensland, St. Lucia, Queensland 4072, Australia.
authors.forename: Rohan D
authors.initials: RD
authors.lastname: Teasdale
authors.affiliation: From the Institute for Molecular Bioscience, University of Queensland, St. Lucia, Queensland 4072, Australia b.collins@imb.uq.edu.au.
authors.forename: Brett M
authors.initials: BM
authors.lastname: Collins
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D011992:Endosomes / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010716:Phosphatidylinositols / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D053838:Scattering, Small Angle; D016415:Sequence Alignment; D058305:Sorting Nexins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D010716:Phosphatidylinositols; C000600447:SNX20 protein, mouse; C000600448:SNX21 protein, mouse; D058305:Sorting Nexins
keywords: X-ray crystallography; endosome; membrane trafficking; phosphoinositide; small-angle x-ray scattering (SAXS); sorting nexin; tetratricopeptide repeat