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Updated: Aug 4, 2026

Preparation of Quality Inositol Pyrophosphates
Published on: September 3, 2011
Inositol hexakisphosphate binds to clathrin assembly protein 3 (AP-3/AP180) and inhibits clathrin cage assembly in
F A Norris1, E Ungewickell, P W Majerus
1Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
Abstract:
We have isolated an inositol hexakisphosphate binding protein from rat brain by affinity elution chromatography from Mono S cation exchange resin using 0.1 mM inositol hexakisphosphate (InsP6). The amino acid sequences of six tryptic peptides from the protein were identical to the sequences predicted from the cDNA encoding a previously isolated protein designated as AP-3 or AP180. This protein is localized in nerve endings and promotes assembly of clathrin into coated vesicles. The isolated protein-bound InsP6 with a dissociation constant of 1.2 microM and a stoichiometry of 0.9 mol of InsP6 bound/mol of AP-3. Recombinant AP-3 expressed in Escherichia coli also bound InsP6 with a similar affinity. InsP6 inhibited clathrin cage assembly mediated by AP-3, in an in vitro assay, but had little effect AP-3 binding to preformed cages. We speculate that InsP6 and perhaps highly phosphorylated inositol lipids may play a role in coated vesicle formation.
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