Cloning, characterization and tissue distribution of the rat ATP-binding cassette (ABC) transporter ABC2/ABCA2

The ABC1 (ABCA) subfamily of the ATP-binding cassette (ABC) transporter sup erfamily has a structural feature that distinguishes it from other ABC tran sporters. Here we report the cloning, molecular characterization and tissue distribution of ABC2/ABCA2, which belongs to the ABC1 subfamily. Rat ABC2 is a protein of 2434 amino acids that has 44.5%, 40.0% and 40.8% identity w ith mouse ABC1/ABCA1, human ABC3/ABCA3 and human ABCR/ABCA4 respectively. I mmunoblot analysis showed that proteins of 260 and 250 kDa were detected in COS-1 cells transfected with ABC2 having a haemagglutinin tag, while no ba nd was detected in mock-transfected cells. After incubation with N-glycosid ase F, the mobilities of the two proteins increased and a single band was d etected, suggesting that ABC2 is a glycoprotein. Photoaffinity labelling wi th 8-azido-[alpha-P-32]ATP confirmed that ATP binds to the ABC2 protein in the presence of Mg2+. RNA blot analysis showed that ABC2 mRNA is most abund ant in rat brain. Examination of brain by in situ hybridization determined that ABC2 is expressed at high levels in the white matter, indicating that it is expressed in the oligodendrocytes. ABC2, therefore, is a glycosylated ABC transporter protein, and may play an especially important role in the brain. In addition, the N-terminal 60-amino-acid sequence of the human ABC1 , which was missing from previous reports, has been determined.