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Biochem Biophys Res Commun. 2001 Nov 16;288(5):1258-64.

Characterization of the ATPase cycle of human ABCA1: implications for its function as a regulator rather than an active transporter.

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National Institute of Haematology and Immunology, Membrane Research Group of the Hungarian Academy of Sciences, Daróczi út 24, H-113 Budapest, Hungary.


ABCA1 plays a key role in cellular cholesterol and phospholipid traffic. To explore the biochemical properties of this membrane protein we applied a Baculovirus-insect cell expression system. We found that human ABCA1 in isolated membranes showed a specific, Mg(2+)-dependent ATP binding but had no measurable ATPase activity. Nevertheless, conformational changes in ABCA1 could be demonstrated by nucleotide occlusion, even without arresting the catalytic cycle by phosphate-mimicking anions. Addition of potential lipid substrates or lipid acceptors (apolipoprotein A-I) did not modify the ATPase activity or nucleotide occlusion by ABCA1. Our data indicate that ATP hydrolysis by ABCA1 occurs at a very low rate, suggesting that ABCA1 may not function as an effective active transporter as previously assumed. In the light of the observed conformational changes we propose a regulatory function for human ABCA1.

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