Functional expression and characterization of the human ABCG1 and ABCG4 proteins: indications for heterodimerization.
The closely related human ABC half-transporters, ABCG1 and ABCG4, have been suggested to play an important role in cellular lipid/sterol regulation but no experimental data for their expression or function are available. We expressed ABCG1 and ABCG4 and their catalytic site mutant variants in insect cells, generated specific antibodies, and analyzed their function in isolated membrane preparations. ABCG1 had a high basal ATPase activity, further stimulated by lipophilic cations and significantly inhibited by cyclosporin A, thyroxine or benzamil. ABCG4 had a lower basal ATPase activity which was not modulated by any of the tested compounds. The catalytic site (K-M) mutants had no ATPase activity. Since dimerization is a requirement for half-transporters, we suggest that both ABCG1 and ABCG4 function as homodimers. Importantly, we also found that co-expression of the ABCG4-KM mutant selectively abolished the ATPase activity of the ABCG1 and therefore they most probably also heterodimerize. The heterologous expression, specific recognition, and functional characterization of these transporters should help to delineate their physiological role and mechanism of action.
Cserepes
Judit
J
Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Hungary.
Szentpétery
Zsófia
Z
Seres
László
L
Ozvegy-Laczka
Csilla
C
Langmann
Thomas
T
Schmitz
Gerd
G
Glavinas
Hristos
H
Klein
Izabella
I
Homolya
László
L
Váradi
András
A
Sarkadi
Balázs
B
Elkind
N Barry
NB
D000070996:ATP Binding Cassette Transporter, Subfamily G; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D019281:Dimerization; D004330:Drosophila / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology
C419353:ABCG1 protein, human; C439766:ABCG4 protein, human; D000070996:ATP Binding Cassette Transporter, Subfamily G; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D011994:Recombinant Proteins; D014638:Vanadates; D000251:Adenosine Triphosphatases