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The beta-appendages of the four adaptor-protein (AP) complexes: structure and binding properties, and identification of sorting nexin 9 as an accessory protein to AP-2
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
2002 (English)In: Biochemical Journal, ISSN 0264-6021, E-ISSN 1470-8728, Vol. 362, no 3, 597-607 p.Article in journal (Refereed) Published
Abstract [en]

Adaptor protein (AP) complexes are essential components for the formation of coated vesicles and the recognition of cargo proteins for intracellular transport. Each AP complex exposes two appendage domains with that function to bind regulatory accessory proteins in the cytosol. Secondary structure predictions, sequence alignments and CD spectroscopy were used to relate the beta-appendages of all human AP complexes to the previously published crystal structure of AP-2. The results suggested that the beta-appendages of AP-1, AP-2 and AP-3 have similar structures, consisting of two subdomains, whereas that of AP-4 lacks the inner subdomain. Pull-down and overlay assays showed partial overlap in the binding specificities of the beta-appendages of AP-1 and AP-2, whereas the corresponding domain of AP-3 displayed a unique binding pattern. That AP-4 may have a truncated, non-functional domain was indicated by its apparent inability to bind any proteins from cytosol. Of several novel beta-appendage-binding proteins detected, one that had affinity exclusively for AP-2 was identified as sorting nexin 9 (SNX9). SNX9, which contains a phox and an Src homology 3 domain, was found in large complexes and was at least partially associated with AP-2 in the cytosol. SNX9 may function to assist AP-2 in its role at the plasma membrane.

Place, publisher, year, edition, pages
2002. Vol. 362, no 3, 597-607 p.
Keyword [en]
adaptin, coated vesicle, endocytosis, intracellular transport
National Category
Medical and Health Sciences
URN: urn:nbn:se:umu:diva-3750PubMedID: 11879186OAI: diva2:142597
Available from: 2004-02-18 Created: 2004-02-18 Last updated: 2010-08-06Bibliographically approved
In thesis
1. Sorting nexin 9 in clathrin-mediated endocytosis
Open this publication in new window or tab >>Sorting nexin 9 in clathrin-mediated endocytosis
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Clathrin-mediated endocytosis is a process by which cells can internalise diverse molecules such as nutrients, antigens and signalling-surface receptors. The creation of clathrin-coated vesicles demands interplay between the plasma membrane lipids, cargo molecules and the proteins that build up the coat.

This thesis deals with the identification and characterisation of sorting nexin 9 (SNX9) as a novel component of the endocytic machinery. SNX9 belongs to a large family of proteins based on the presence of a PX domain. In addition, SNX9 harbours an SH3 domain followed by a region with predicted low-complexity and a C-terminal BAR homology domain.

Binding studies demonstrated that SNX9 interacted with the endocytic core components clathrin and AP-2 and dynamin-2, a GTPase known to be crucial for vesicle scission. The C-terminal region bound to phosphatidylinositols and targeted SNX9 to artificial liposomes and cellular membranes.

Consistent with a role in endocytosis, a large portion of SNX9 co-localised with AP-2 and dynamin-2 but not with markers for early endosomes, Golgi. Over-expression of truncated variants of SNX9 in K562 and HeLa cells interfered with the uptake of transferrin.

SNX9 recycles between a membrane-bound and a cytosolic pool. In cytosol, SNX9 formed a resting complex together with dynamin-2 and the metabolic enzyme aldolase. Activation for membrane binding involved ATP hydrolysis and correlated with phosphorylation of SNX9 and the release of aldolase. Aldolase bound to a tryptophan-containing acidic region near the clathrin and AP-2 motifs and blocked lipid binding of purified SNX9 derivatives. SNX9 was required for membrane targeting of dynamin2 in vitro and knockdown of SNX9 in HeLa cells by RNAi resulted in impaired membrane localisation. Together these results argue strongly for a role of SNX9 in recruiting and linking of dynamin-2 to sites of vesicle creation.

Place, publisher, year, edition, pages
Umeå: Medicinsk biokemi och biofysik, 2004. 37 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 875
Cell and molecular biology, sorting nexin, dynamin, clathrin, endocytosis, human, adaptor protein complexes, Cell- och molekylärbiologi
National Category
Biochemistry and Molecular Biology
Research subject
Medical Biochemistry
urn:nbn:se:umu:diva-197 (URN)91-7305-599-9 (ISBN)
Public defence
2004-03-05, KB3A9, KBC huset, Umeå, 09:00
Available from: 2004-02-18 Created: 2004-02-18 Last updated: 2010-08-06Bibliographically approved

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Lundmark, RichardCarlsson, Sven
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