A pH-dependent conformational transition of Abeta peptide and physicochemical properties of the conformers in the glial cell.
In the present study we identified the epitopes of antibodies against amyloid beta-(1-42)-peptide (Abeta1-42): 4G8 reacted with peptides corresponding to residues 17-21, 6F/3D reacted with peptides corresponding to residues 9-14, and anti 5-10 reacted with peptides corresponding to residues 5-10. The study also yielded some insight into the Abeta1-42 structures resulting from differences in pH. An ELISA study using monoclonal antibodies showed that pH-dependent conformational changes occur in the 6F/3D and 4G8 epitopes modified at pH 4.6, but not in the sequences recognized by anti 1-7 and anti 5-10. This was unique to Abeta1-40 and Abeta1-42 and did not occur with Abeta1-16 or Abeta17-42. The reactivity profile of 4G8 was not affected by blockage of histidine residues of pH-modified Abeta1-40 and Abeta1-42 with diethyl pyrocarbonate; however, the mutant [Gln(11)]Abeta1-40 abrogated the unique pH-dependence towards 4G8 observed with Abeta1-40. These findings suggest that these epitopes are cryptic at pH 4.6, and that Glu(11) is responsible for the changes. We suggest that the abnormal folding of 6F/3D epitope affected by pH masked the 4G8 epitope. A study of the binding of metal ions to Abeta1-42 suggested that Cu(2+) and Zn(2+) induced a conformational transition around the 6F/3D region at pH 7.4, but did not affect the region when it was modified at pH 4.6. However, Fe(2+) had no effect, irrespective of pH. Abeta modified at pH 4.6 appeared to be relatively resistant to proteinase K compared with Abetas modified at pH 7.4, and the former might be preferentially internalized and accumulated in a human glial cell. Our findings suggest the importance of microenvironmental changes, such as pH, in the early stage of formation of Abeta aggregates in the glial cell.
Matsunaga
Yoichi
Y
Fifth Department of Internal Medicine, School of Medicine, Fukuoka University, 7-45-1 Nanakuma, Jonan-ku, Fukuoka 814-0133, Japan. yoichima@fukuoka-u.ac.jp
Saito
Nobuhiro
N
Fujii
Akihiro
A
Yokotani
Junichi
J
Takakura
Tadakazu
T
Nishimura
Tomoaki
T
Esaki
Hiroyuki
H
Yamada
Tatsuo
T
D000544:Alzheimer Disease / Q000378:metabolism; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D000911:Antibodies, Monoclonal / Q000378:metabolism; D015153:Blotting, Western; D002460:Cell Line; D003720:Densitometry; D004797:Enzyme-Linked Immunosorbent Assay; D018604:Epitope Mapping; D000939:Epitopes; D006639:Histidine / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D008969:Molecular Sequence Data; D009457:Neuroglia / Q000166:cytology*; D010452:Peptide Biosynthesis; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
D000596:Amino Acids; D016229:Amyloid beta-Peptides; D000911:Antibodies, Monoclonal; D000939:Epitopes; D006639:Histidine; D007501:Iron