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Inositol polyphosphate receptor and clathrin assembly protein AP-2 are related proteins that form potassium-selective ion channels in planar lipid bilayers.

Authors
  • Timerman, A P
  • Mayrleitner, M M
  • Lukas, T J
  • Chadwick, C C
  • Saito, A
  • Watterson, D M
  • Schindler, H
  • Fleischer, S
Type
Published Article
Journal
Proceedings of the National Academy of Sciences of the United States of America
Publication Date
Oct 01, 1992
Volume
89
Issue
19
Pages
8976–8980
Identifiers
PMID: 1329085
Source
Medline
License
Unknown

Abstract

We have previously described an inositol polyphosphate receptor (IPxRec), purified from detergent-solubilized bovine cerebellum microsomes, that displays potassium ion channel activity in planar lipid bilayers. We now find that the IPxRec is closely related to clathrin assembly protein AP-2. The IPxRec and AP-2 purified from bovine brain clathrin-coated vesicles share several structural and functional features: (i) similar subunit composition; each has four major polypeptides that have similar mobility (Mr values of 111,000, 100,000, 50,000, and 17,000) and relative intensity by SDS/PAGE analysis; (ii) similar size as studied by molecular sieve chromatography (Mr 400,000); (iii) identical N-terminal amino acid sequences for the Mr 50,000 subunits and Mr 111,000/100,000 doublets; (iv) immunoreactivity of the AP-2 Mr 111,000/100,000 doublet to polyclonal antibodies affinity purified against the doublet proteins of the IPxRec; (v) display of the in vitro diagnostic feature of assembly proteins--i.e., they induce the assembly of clathrin cages; and (vi) ion channel activity selective for potassium ions with the same unitary conductance when incorporated into planar lipid bilayers. One difference was found. AP-2 channels were not blocked by inositol 1,3,4,5-tetraphosphate as reported for IPx receptor channels. These studies suggest a possible connection between the IPx signaling pathways and receptor-mediated endocytosis.

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