title: The structure of apolipoprotein A-II in discoidal high density lipoproteins.
abstract: It is well accepted that high levels of high density lipoproteins (HDL) reduce the risk of atherosclerosis in humans. Apolipoprotein A-I (apoA-I) and apoA-II are the first and second most common protein constituents of HDL. Unlike apoA-I, detailed structural models for apoA-II in HDL are not available. Here, we present a structural model of apoA-II in reconstituted HDL (rHDL) based on two well established experimental approaches: chemical cross-linking/mass spectrometry (MS) and internal reflection infrared spectroscopy. Homogeneous apoA-II rHDL were reacted with a cross-linking agent to link proximal lysine residues. Upon tryptic digestion, cross-linked peptides were identified by electrospray mass spectrometry. 14 cross-links were identified and confirmed by tandem mass spectrometry (MS/MS). Infrared spectroscopy indicated a beltlike molecular arrangement for apoA-II in which the protein helices wrap around the lipid bilayer rHDL disc. The cross-links were then evaluated on three potential belt arrangements. The data clearly refute a parallel model but support two antiparallel models, especially a "double hairpin" form. These models form the basis for understanding apoA-II structure in more complex HDL particles.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237.
authors.forename: R A Gangani D
authors.initials: RAGD
authors.lastname: Silva
authors.affiliation: Departments of Pharmacology, Biochemistry, and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Lumelle A
authors.initials: LA
authors.lastname: Schneeweis
authors.affiliation: Mass Spectrometry Application Laboratory, Applied Biosystems, Framingham, Massachusetts 01701.
authors.forename: Srinivasan C
authors.initials: SC
authors.lastname: Krishnan
authors.affiliation: Department of Chemistry, University of Illinois, Chicago, Illinois 60607.
authors.forename: Xiuqi
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Departments of Pharmacology, Biochemistry, and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Axelsen
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237. Electronic address: Sean.Davidson@UC.edu.
authors.forename: W Sean
authors.initials: WS
authors.lastname: Davidson
mesh_terms: D016633:Apolipoprotein A-II / Q000737:chemistry* / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000378:metabolism; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008074:Lipoproteins / Q000737:chemistry* / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D013329:Structure-Activity Relationship
chemical_list: D016633:Apolipoprotein A-II; D003432:Cross-Linking Reagents; D008051:Lipid Bilayers; D008074:Lipoproteins; D008075:Lipoproteins, HDL; C034366:discoidal lipoproteins