Author： Szakács G. Langmann T. Özvegy C. Orsó E. Schmitz G. Váradi A. Sarkadi B.
Publisher： Elsevier
ISSN： 0006-291X
Source： Biochemical and Biophysical Research Communications, Vol.288, Iss.5, 2001-11, pp. : 1258-1264
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Abstract
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, Mg2+-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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