The specific amino acid sequence between helices 7 and 8 influences the binding specificity of human apolipoprotein A-I for high density lipoprotein (HDL) subclasses: a potential for HDL preferential generation.
Humans have two major high density lipoprotein (HDL) sub-fractions, HDL(2) and HDL(3), whereas mice have a monodisperse HDL profile. Epidemiological evidence has suggested that HDL(2) is more atheroprotective; however, currently there is no direct experimental evidence to support this postulate. The amino acid sequence of apoA-I is a primary determinant of HDL subclass formation. The majority of the alpha-helical repeats in human apoA-I are proline-punctuated. A notable exception is the boundary between helices 7 and 8, which is located in the transitional segment between the stable N-terminal domain and the C-terminal hydrophobic domain. In this study we ask whether the substitution of a proline-containing sequence (PCS) separating other helices in human apoA-I for the non-proline-containing sequence (NPCS) between helices 7 and 8 (residues 184-190) influences HDL subclass association. The human apoA-I mutant with PCS2 replacing NPCS preferentially bound to HDL(2). In contrast, the mutant where PCS3 replaced NPCS preferentially associated with HDL(3). Thus, the specific amino acid sequence between helices 7 and 8 influences HDL subclass association. The wild-type and mutant proteins exhibited similar physicochemical properties except that the two mutants displayed greater lipid-associated stability versus wild-type human apoA-I. These results focus new attention on the influence of the boundary between helices 7 and 8 on the properties of apoA-I. The expression of these mutants in mice may result in the preferential generation of HDL(2) or HDL(3) and allow us to examine experimentally the anti-atherogenicity of the HDL subclasses.
Carnemolla
Ronald
R
Department of Pathology, The University of Chicago, Chicago, Illinois 60637, USA.
Ren
Xuefeng
X
Biswas
Tapan K
TK
Meredith
Stephen C
SC
Reardon
Catherine A
CA
Wang
Jianjun
J
Getz
Godfrey S
GS
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D053439:Lipoproteins, HDL2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D053440:Lipoproteins, HDL3 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009154:Mutation; D011485:Protein Binding / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D013045:Species Specificity
D016632:Apolipoprotein A-I; D053439:Lipoproteins, HDL2; D053440:Lipoproteins, HDL3