Apolipoprotein A-I alpha -helices 7 and 8 modulate high density lipoprotein subclass distribution.
Mice have a monodisperse high density lipoprotein (HDL) profile, whereas humans have two major subfractions designated HDL(2) and HDL(3). Human apoA-I transgenic mice exhibit a human-like HDL profile, indicating that the amino acid sequence of apoA-I is a determinant of the HDL profile. Comparison of the primary sequence of mouse and human apoA-I and the previously designated "hinge" domain of apoA-I led us to hypothesize that alpha-helices 7 and 8 (7/8) are determinants of HDL subclass distribution. The following proteins were expressed in Escherichia coli: human apoA-I, T7-hAI; mouse apoA-I, T7-mAI; chimeric human apoA-I containing murine helices 7/8 in place of human helices 7/8, T7-hAI(m7/8); and the reciprocal chimera, T7-mAI(h7/8). The recombinant proteins were examined for their association with human plasma HDL subclasses. The results demonstrated that T7-hAI bound HDL(2) and HDL(3) equally well, whereas T7-mAI bound to HDL(2) preferentially. T7-hAI(m7/8) behaved like T7-mAI, and T7-mAI(h7/8) behaved like T7-hAI. Thus, alpha-helices 7/8 are strong contributors to the pattern of HDL subclass association. Self-association, alpha-helicity, cholesterol efflux, and lecithin-cholesterol acyltransferase activity of the recombinant proteins were also assessed. Human apoA-I self-associates more and activates human lecithin-cholesterol acyltransferase better than mouse apoA-I. These differential characteristics of human and mouse apoA-I are not dependent on helices 7/8.
Reschly
Erica J
EJ
Department of Pathology, University of Chicago, Chicago, Illinois 60637, USA.
Sorci-Thomas
Mary G
MG
Davidson
W Sean
WS
Meredith
Stephen C
SC
Reardon
Catherine A
CA
Getz
Godfrey S
GS
D000595:Amino Acid Sequence; D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000378:metabolism; D015153:Blotting, Western; D002784:Cholesterol / Q000378:metabolism; D008076:Cholesterol, HDL / Q000737:chemistry*; D002942:Circular Dichroism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000737:chemistry*; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D016632:Apolipoprotein A-I; D008076:Cholesterol, HDL; D003432:Cross-Linking Reagents; D018076:DNA, Complementary; D008075:Lipoproteins, HDL; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D002784:Cholesterol