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 β-appendages of all human AP complexes to the previously published crystal structure of AP-2. The results suggested that the β-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 β-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 β-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.
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March 2002
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Research Article|
March 08 2002
The β-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
Richard LUNDMARK;
Richard LUNDMARK
Department of Medical Biochemistry and Biophysics, Umeå University, S-901 87 Umeå, Sweden
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Sven R. CARLSSON
Sven R. CARLSSON
1
Department of Medical Biochemistry and Biophysics, Umeå University, S-901 87 Umeå, Sweden
1To whom correspondence should be addressed (e-mail sven.carlsson@medkem.umu.se).
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Publisher: Portland Press Ltd
Received:
October 08 2001
Revision Received:
November 20 2001
Accepted:
December 13 2001
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London ©2002
2002
Biochem J (2002) 362 (3): 597–607.
Article history
Received:
October 08 2001
Revision Received:
November 20 2001
Accepted:
December 13 2001
Citation
Richard LUNDMARK, Sven R. CARLSSON; The β-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. Biochem J 15 March 2002; 362 (3): 597–607. doi: https://doi.org/10.1042/bj3620597
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