Conformations of synthetic beta peptides in solid state and in aqueous solution: relation to toxicity in PC12 cells.
The secondary structures of peptides beta 25-35 (the active toxic fragment) and beta 35-25 (reverse sequence and non-toxic fragment), as well as of the amidated beta (25-35)-NH2 peptide were investigated in aqueous solution and in the solid state by means of Fourier-transformed infrared spectroscopy and circular dichroism spectroscopy. The conformations of the beta 25-35 and beta 35-25 in solid state were identical and contained mostly beta-sheet structures. In solid state the amidated beta (25-35)-NH2 peptide also contained mostly beta-sheet structures. Freshly prepared aqueous solutions of the beta 25-32 (0.5 - 3.8 mM) contained a mixture of beta-sheet and random coil structures. Within 30-60 min incubation at 37 degrees C in water or in phosphate-buffered saline solution (PBS), beta 25-35 was almost fully converted to a beta-sheet structure. Decreasing the temperature from 37 degrees C to 20 degrees C decreased the rate of conversion from random coil to beta-sheet structures, 1-2 h being required for complete conversion. In contrast beta 35-25 in water or in PBS buffer had mostly a random coil structure and remained so for 6 days. The amidated beta(25-35)-NH2 peptide in water (2.7 mM) was also mostly random coil. However, when this peptide (2-2.7 mM) was dissolved in PBS (pH 7.4) or in 140 mM NaCl, a gel was formed and its conformation was mostly beta-sheet. Decreasing the concentration of beta (25-35)-NH2 peptide in 140 mM NaCl aqueous solution from 2 mM to 1 mM or below favored the conversion from beta-sheet structures to random coil structures. The beta 25-35 was toxic to PC12 cells while beta 35-25 was not. The amidated peptide beta (25-35)-NH2 was at least 500-fold less toxic than beta 25-35. Structural differences between these beta peptides in aqueous solutions may explain the difference in their respective toxicities.
Buchet
R
R
Sandoz Research Institute Berne Ltd, Switzerland.
Tavitian
E
E
Ristig
D
D
Swoboda
R
R
Stauss
U
U
Gremlich
H U
HU
de La Fournière
L
L
Staufenbiel
M
M
Frey
P
P
Lowe
D A
DA
D000577:Amides / Q000737:chemistry / Q000633:toxicity; D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000633:toxicity; D000818:Animals; D002470:Cell Survival / Q000187:drug effects*; D002942:Circular Dichroism; D016716:PC12 Cells; D010446:Peptide Fragments / Q000737:chemistry* / Q000633:toxicity; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D051381:Rats; D017550:Spectroscopy, Fourier Transform Infrared
D000577:Amides; D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C074636:amyloid beta-protein (25-35)