Inositol polyphosphate receptor and clathrin assembly protein AP-2 are related proteins that form potassium-selective ion channels in planar lipid bilayers.
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.
Timerman
A P
AP
Department of Molecular Biology, College of Medicine, Vanderbilt University, Nashville, TN 37235.
Mayrleitner
M M
MM
Lukas
T J
TJ
Chadwick
C C
CC
Saito
A
A
Watterson
D M
DM
Schindler
H
H
Fleischer
S
S
D033942:Adaptor Proteins, Vesicular Transport; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002531:Cerebellum / Q000502:physiology; D002846:Chromatography, Affinity; D002966:Clathrin / Q000502:physiology*; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D008861:Microsomes / Q000502:physiology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010750:Phosphoproteins / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D017386:Sequence Homology, Amino Acid
D033942:Adaptor Proteins, Vesicular Transport; D002966:Clathrin; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D010750:Phosphoproteins; D015221:Potassium Channels; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; C072844:inositol polyphosphate receptor