Identification of binding proteins for cholesterol absorption inhibitors as components of the intestinal cholesterol transporter

To identify protein components of the intestinal cholesterol transporter, r abbit small intestinal brush border membrane vesicles were submitted to pho toaffinity labeling using photoreactive derivatives of 2-azetidinone choles terol absorption inhibitors. An integral membrane protein of M-r 145.3 +/- 7.5 kDa was specifically labeled in brush border membrane vesicles from rab bit jejunum and ileum. Its labeling was concentration-dependently inhibited by the presence of cholesterol absorption inhibitors whereas bile acids, D -glucose, fatty acids or cephalexin had no effect. The inhibitory potency o f 2-azetidinones to inhibit photolabeling of the 145 kDa protein correlated with their in vivo activity to inhibit intestinal cholesterol absorption. These results suggest that an integral membrane protein of M-r, 145 kDa is (a component of) the cholesterol absorption system in the brush border memb rane of small intestinal enterocytes. (C) 2000 Federation of European Bioch emical Societies. Published by Elsevier Science B.V. All rights reserved.