C-reactive protein binds to the 3b-OH group of cholesterol in LDL particles Sanna Taskinen a , Marja Hyvo ¨nen a , Petri T. Kovanen a, * , Seppo Meri b , Markku O. Pentika ¨inen a a Wihuri Research Institute, Kalliolinnantie 4, FIN-00140 Helsinki, Finland b Department of Bacteriology and Immunology, University of Helsinki, Helsinki, Finland Received 3 February 2005 Abstract C-reactive protein (CRP) has been suggested to contribute to the development of atherosclerosis. We previously found binding of CRP to cholesterol in modified low density lipoprotein (LDL) particles. Here, we characterize the interaction between CRP and cholesterol in more detail. When lipids of native LDL were separated by thin-layer chromatography, CRP bound only to choles- terol. When various cholesterol analogues were compared for their ability to bind CRP, we found that any modification of the 3b-OH group blocked binding of CRP to cholesterol. Similarly, enrichment of LDL with cholesterol but not with its analogues trig- gered the binding of CRP to LDL. Finally, with the aid of anti-CRP monoclonal antibodies and by molecular modeling, we obtained evidence for involvement of the phosphorylcholine-binding site of CRP in cholesterol binding. Thus, CRP can bind to cholesterol, and the interaction is mediated by the phosphorylcholine-binding site of CRP and the 3b-hydroxyl group of cholesterol. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Low-density lipoprotein; C-reactive protein; Cholesterol; Acute-phase response; Atherosclerosis; Inflammation The pentraxin C-reactive protein (CRP) [1] is an acute-phase reactant produced mainly in the liver in re- sponse to proinflammatory cytokines, notably IL-6 and IL-1b. Plasma CRP levels are increased in patients with coronary heart disease and the increased CRP levels pre- dict their outcome [1]. CRP is not only a marker of inflammation, but it has been shown to possess biologi- cal functions, including direct opsonization and regula- tion of complement activation [2–4]. CRP is deposited in atherosclerotic lesions, where it may actively partici- pate in various atherosclerotic processes. Thus, CRP has been shown to co-localize with complement deposits [5], suggesting local complement activation in the le- sions. Indeed, apolipoprotein E-knockout mice trans- genic for human CRP had to some extent accelerated progression of atherosclerosis compared to their non- transgenic littermates, with increased complement depo- sition in atherosclerotic lesions [6]. How CRP is deposited in atherosclerotic lesions is not known. It is likely that, in addition to CRP infiltra- tion from blood plasma to the arterial intima, at least some of the CRP in the arterial intima is produced lo- cally [7]. The target structures for CRP in the arterial in- tima include lipoproteins, and apoptotic and necrotic cells. Studies on the binding of CRP to lipoproteins have been controversial. CRP has been reported to bind to immobilized low density lipoprotein (LDL) and very low density lipoprotein particles [8], but more recent studies have indicated that CRP does not interact with lipoproteins in their native conformation [9], but rather [10,11] binds to LDL modified enzymatically [9,10] or by oxidation [11]. The classical ligand for CRP is phospho- rylcholine, and the recent study by Chang et al. [11] 0006-291X/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2005.02.091 * Corresponding author. Fax: +358 9 637 476. E-mail address: petri.kovanen@wri.fi (P.T. Kovanen). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 329 (2005) 1208–1216 BBRC