Structure of human apolipoprotein D: locations of the intermolecular and intramolecular disulfide links.
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.
Yang
C Y
CY
Baylor College of Medicine, Houston, Texas 77030.
Gu
Z W
ZW
Blanco-Vaca
F
F
Gaskell
S J
SJ
Yang
M
M
Massey
J B
JB
Gotto
A M
AM
Pownall
H J
HJ
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
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