Structural variation in human apolipoprotein E3 and E4: secondary structure, tertiary structure, and size distribution.
Human apolipoprotein E (apoE) is a 299-amino-acid protein with a molecular weight of 34 kDa. The difference between the apoE3 and apoE4 isoforms is a single residue substitution involving a Cys-Arg replacement at residue 112. ApoE4 is positively associated with atherosclerosis and late-onset and sporadic Alzheimer's disease (AD). ApoE4 and its C-terminal truncated fragments have been found in the senile plaques and neurofibrillary tangles in the brain of AD patients. However, detail structural information regarding isoform and domain interaction remains poorly understood. We prepared full-length, N-, and C-terminal truncated apoE3 and apoE4 proteins and studied their structural variation. Sedimentation velocity and continuous size distribution analysis using analytical ultracentrifugation revealed apoE3(72-299) as consisting of a major species with a sedimentation coefficient of 5.9. ApoE4(72-299) showed a wider and more complicated species distribution. Both apoE3 and E4 N-terminal domain (1-191) existed with monomers as the major component together with some tetramer. The oligomerization and aggregation of apoE protein increased when the C-terminal domain (192-271) was incorporated. The structural influence of the C-terminal domain on apoE is to assist self-association with no significant isoform preference. Circular dichroism and fluorescence studies demonstrated that apoE4(72-299) possessed a more alpha-helical structure with more hydrophobic residue exposure. The structural variation of the N-terminal truncated apoE3 and apoE4 protein provides useful information that helps to explain the greater aggregation of the apoE4 isoform and thus has implication for the involvement of apoE4 in AD.
Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan.
Chi-Yuan
CY
Chou
Yi-Ling
YL
Lin
Yu-Chyi
YC
Huang
Sheh-Yi
SY
Sheu
Ta-Hsien
TH
Lin
Huey-Jen
HJ
Tsay
Gu-Gang
GG
Chang
Ming-Shi
MS
Shiao
D000483:Alleles; D000544:Alzheimer Disease / Q000378:metabolism; D000817:Anilino Naphthalenesulfonates / Q000494:pharmacology; D053318:Apolipoprotein E3; D001053:Apolipoproteins / Q000737:chemistry; D001054:Apolipoproteins A / Q000737:chemistry*; D001057:Apolipoproteins E / Q000737:chemistry*; D001120:Arginine / Q000737:chemistry; D001161:Arteriosclerosis / Q000378:metabolism; D001703:Biophysics / Q000379:methods*; D001921:Brain / Q000378:metabolism; D002021:Buffers; D002942:Circular Dichroism; D003545:Cysteine / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D005822:Genetic Vectors; D006801:Humans; D008027:Light; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D015233:Models, Statistical; D010957:Plasmids / Q000378:metabolism; D011487:Protein Conformation; D020033:Protein Isoforms; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence
D000817:Anilino Naphthalenesulfonates; D053318:Apolipoprotein E3; D001053:Apolipoproteins; D001054:Apolipoproteins A; D001057:Apolipoproteins E; D002021:Buffers; D020033:Protein Isoforms; C022205:apolipoprotein A-IV; D001120:Arginine; D003545:Cysteine