tailieunhanh - Báo cáo khoa học: The Alzheimer b-peptide shows temperature-dependent transitions between left-handed 31-helix, b-strand and random coil secondary structures

The temperature-induced structural transitions of the full length Alzheimer amyloid b-peptide [Ab(1–40) peptide] and fragments of it were studied using CD and 1 H NMR spectroscopy. The full length peptide undergoes an overall transition from a state with a prominent population of left-handed 31 (polyproline II; PII)-helix at 0 C to a random coil state at 60 C, with an averageDH of ± kJÆmol )1 per residue, obtained by fitting a Zimm–Bragg model to the CD data. | iFEBS Journal The Alzheimer b-peptide shows temperature-dependent transitions between left-handed 31-helix b-strand and random coil secondary structures Jens Danielsson Juri Jarvet Peter Damberg and Astrid Graslund Department of Biochemistry and Biophysics Stockholm University Sweden Keywords amyloid b-peptide b-strand left-handed 31-helix random coil transition enthalpy Correspondence A. Graslund Department of Biochemistry and Biophysics Stockholm University S-106 91 Stockholm Sweden E-mail astrid@ Received 13 April2005 revised 26 May 2005 accepted 9 June 2005 doi The temperature-induced structural transitions of the full length Alzheimer amyloid b-peptide Ab 1-40 peptide and fragments of it were studied using CD and 1H NMR spectroscopy. The full length peptide undergoes an overall transition from a state with a prominent population of lefthanded 31 polyproline II PII -helix at 0 C to a random coil state at 60 C with an average AH of kJ-mol-1 per residue obtained by fitting a Zimm-Bragg model to the CD data. The transition is noncooperative for the shortest N-terminal fragment Ab 1-9 and weakly cooperative for Ab 1-40 and the longer fragments. By analysing the temperaturedependent 3JHNHa couplings and hydrodynamic radii obtained by NMR for Ab 1-9 and Ab 12-28 we found that the structure transition includes more than two states. The N-terminal hydrophilic Ab 1-9 populates PII-like conformations at 0 C then when the temperature increases conformations with dihedral angles moving towards b-strand at 20 C and approaches random coil at 60 C. The residues in the central hydrophobic 18-28 segment show varying behaviour but there is a significant contribution of b-strand-like conformations at all temperatures below 20 C. The C-terminal 29-40 segment was not studied by NMR but from CD difference spectra we concluded that it is mainly in a random coil conformation at all studied temperatures. These results on structural .

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