PubMed · 12402033
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Victor Muñoz. 2002. Folding plasticity.. https://doi.org/10.1038/nsb1102-792
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Ultrafast IR spectroscopy is used to monitor the nonequilibrium backbone dynamics of a cyclic peptide in the amide I vibrational range with picosecond time resolution. A conformational change is induced by means of a photoswitch integrated into the peptide backbone. Although the main conformational change of the backbone is completed after only 20 ps, the subsequent equilibration in the new region of conformational space continues for times >16 ns. Relaxation and equilibration processes of the peptide backbone occur on a discrete hierarchy of time scales. Albeit possessing only a few conformational degrees of freedom compared with a protein, the peptide behaves highly nontrivially and provides insights into the complexity of fast protein folding.
This paper reported an ongoing study of cyclic peptides as carriers of potential anti-tumor agents. In an effort to carry out anti-cancer drug design, we synthesized another novel cyclic peptide as the analogue of the cyclic peptide in Triostin A. The linear peptide chains were synthesized by coupling protected amino acid residues according to Pfp/DCC methods (Pfp: Pentafluorophenol, DCC: N,N'-Dicyclohexyl-carbodiimide) in solution. After deblocking the Boc- group of the linear octapeptide chain, the cyclic product was achieved by employing diphenylphosphoryl azide (DPPA) as cyclic agent at low temperature in DMF. Further study on cyclic octapeptide-drug conjugates is in progress.
cyclo(L-Leucyl-L-phenylalanyl-glycyl-D-phenylalanyl-L-leucyl-glycyl-) trihydrate (IV), C34H46N6O6.-3H2O, Mr = 688.8, monoclinic, P2(1), a = 11.720 (2), b = 36.354 (4), c = 8.888 (1) A, beta = 103.88 (1) degree, V = 3676.3 A3, Z = 4, Dx = 1.244 g cm-3, lambda (Cu K alpha) = 1.54178 A, mu = 7.6 cm-1, F(000) = 1480, T = 138 K, final R = 0.052 for 7661 unique reflections. cyclo(L-Phenylalanyl-L-leucyl-glycyl-D-leucyl-L-phenylalanyl-glycyl-) trihydrate (V), C34H46N6O6.-3H2O, Mr = 688.8, triclinic, P1, a = 101.54 (2), b = 19.111 (5), c = 8.527 (1) A, alpha = 101.54 (2), beta = 93.42 (2), gamma = 94.27 (2) degree, V = 1852.4 A3, Z = 2, Dx = 1.235 g cm-3, lambda (Cu K alpha) = 1.54178 A, mu = 7.5 cm-1, F(000) = 740, T = 138 K, final R = 0.063 for 7574 unique reflections. Peptides IV and V both have two independent conformers (molecules A and B). The peptide ring in each case contains one beta (I) turn and one beta (II') turn. A molecules in both structures have two transannular N--H...O hydrogen bonds, while B molecules form only one strong transannular hydrogen bond. The conformational differences between the two independent molecules (A and B) are much larger than the differences between the corresponding molecules of the two structures (A and A, and B and B). The crystal structures of the two peptides are very similar and consist of parallel bands of hydrophobic side chains and polar peptide regions. In each structure, molecules are stacked one over another with the hexapeptide ring lying perpendicular to the axis of the stack. The water molecules form well delimited solvent channels sandwiched between the layers of peptide molecules, and bridge the peptides through extensive hydrogen bonding.