Characterization of oligomeric human half-ABC transporter ATP-binding cassette G2.
Human ATP-binding cassette G2 (ABCG2, also known as mitoxantrone resistance protein, breast cancer-resistance protein, ABC placenta) is a member of the superfamily of ATP-binding cassette (ABC) transporters that have a wide variety of substrates. Overexpression of human ABCG2 in model cancer cell lines causes multidrug resistance by actively effluxing anticancer drugs. Unlike most of the other ABC transporters which usually have two nucleotide-binding domains and two transmembrane domains, ABCG2 consists of only one nucleotide-binding domain followed by one transmembrane domain. Thus, ABCG2 has been thought to be a half-transporter that may function as a homodimer. In this study, we characterized the oligomeric feature of human ABCG2 using non-denaturing detergent perfluoro-octanoic acid and Triton X-100 in combination with gel filtration, sucrose density gradient sedimentation, and gel electrophoresis. Unexpectedly, we found that human ABCG2 exists mainly as a tetramer, with a possibility of a higher form of oligomerization. Monomeric and dimeric ABCG2 did not appear to be the major form of the protein. Further immunoprecipitation analysis showed that the oligomeric ABCG2 did not contain any other proteins. Taken together, we conclude that human ABCG2 likely exists and functions as a homotetramer.
Xu
Junkang
J
Department of Pharmacology and Toxicology, Indiana University Cancer Center, Walther Oncology Center/Walther Cancer Institute, Indiana University School of Medicine, 1044 W. Walnut Street, Indianapolis, IN 46202, USA.
Liu
Yang
Y
Yang
Youyun
Y
Bates
Susan
S
Zhang
Jian-Ting
JT
D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000502:physiology; D002210:Caprylates / Q000494:pharmacology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D002850:Chromatography, Gel; D003432:Cross-Linking Reagents / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D005466:Fluorocarbons / Q000494:pharmacology; D006801:Humans; D009363:Neoplasm Proteins / Q000737:chemistry* / Q000502:physiology; D017830:Octoxynol / Q000494:pharmacology; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D013395:Sucrose / Q000494:pharmacology
C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D002210:Caprylates; D003432:Cross-Linking Reagents; D003902:Detergents; D004220:Disulfides; D005466:Fluorocarbons; D009363:Neoplasm Proteins; D012967:Sodium Dodecyl Sulfate; D013395:Sucrose; D017830:Octoxynol; C023036:perfluorooctanoic acid