title: Structure of human apolipoprotein D: locations of the intermolecular and intramolecular disulfide links.
abstract: We have determined the primary structure of human apolipoprotein D (apoD) by aligning peptides derived from digestions by cyanogen bromide, trypsin, and chymotrypsin. Our results confirm the primary structure derived from cDNA [Drayna et al. (1986) J. Biol. Chem. 261, 16535-16539]. ApoD consists of 169 amino acid residues, including 5 cysteines. Tryptic peptide analysis indicated that Cys41 and Cys16 are joined by a disulfide bridge. Using a combination of manual Edman degradations and mass spectrometric analysis on a purified cluster of chymotryptic fragments, we identified an intramolecular disulfide bridge between Cys8 and Cys114 and an intermolecular bridge between Cys116 of apoD and Cys6 of apoA-II. In addition, sites of N-glycosylation were found at Asn45 and Asn78. Because apoD contains two intramolecular disulfide linkages and has a high content of proline to disrupt alpha-helical structures, formation of the amphipathic helical regions that characterize the other soluble apolipoproteins is unlikely. We conclude that apoD binds to lipoprotein surfaces through structures other than alpha-helices, such as disulfide links.
authors.affiliation: Baylor College of Medicine, Houston, Texas 77030.
authors.forename: C Y
authors.initials: CY
authors.lastname: Yang
authors.forename: Z W
authors.initials: ZW
authors.lastname: Gu
authors.forename: F
authors.initials: F
authors.lastname: Blanco-Vaca
authors.forename: S J
authors.initials: SJ
authors.lastname: Gaskell
authors.forename: M
authors.initials: M
authors.lastname: Yang
authors.forename: J B
authors.initials: JB
authors.lastname: Massey
authors.forename: A M
authors.initials: AM
authors.lastname: Gotto
authors.forename: H J
authors.initials: HJ
authors.lastname: Pownall
mesh_terms: D000595:Amino Acid Sequence; D016633:Apolipoprotein A-II / Q000737:chemistry; D001053:Apolipoproteins / Q000737:chemistry* / Q000378:metabolism; D053399:Apolipoproteins D; D001216:Asparagine / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002918:Chymotrypsin; D003488:Cyanogen Bromide; D003545:Cysteine / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry*; D006031:Glycosylation; D006801:Humans; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D017433:Protein Structure, Secondary; D014357:Trypsin
chemical_list: D016633:Apolipoprotein A-II; D001053:Apolipoproteins; D053399:Apolipoproteins D; D004220:Disulfides; D010446:Peptide Fragments; D001216:Asparagine; D002918:Chymotrypsin; D014357:Trypsin; D003545:Cysteine; D003488:Cyanogen Bromide