Solution conformational analysis of sodium complexed [Gly6]- and [Gly9]-antamanide analogs.
To investigate the conformational flexibility of metal-complexed cyclodecapeptides, we synthesized and studied two antamanide analogs, in which the phenylalanine residue in position 6 or 9 of the sequence was substituted by Gly. Previous conformational studies on antamanide suggested that these backbone regions are affected by conformational variation. The NMR conformational study showed a high degree of flexibility for the two analogs. With sodium ions, on the other hand, [Gly9]-antamanide was able to form a fairly stable equimolar complex, whereas [Gly6]-antamanide showed a conformational heterogeneity, with one prevailing conformer. For the [Gly9]-antamanide analog, the whole NMR data, combined with extensive theoretical calculations, were consistent with the presence of 1) two beta-turns of type I, centered on Gly9-Phe10 and Ala4-Phe5, respectively; 2) a central cavity with a six-carbonyl oxygen cage, optimal for a Na+ hexacoordination; 3) strongly H-bonded amide protons for residues 1 and 6, both involved in the formation of the two type I beta-turns, which, however, exhibited some fluctuations during the molecular dynamics simulations. For the [Gly6]-antamanide-Na+ complex the prevailing conformer was consistent with a more open structure, with the partial solvent exposure of all the amide protons; that is, the Gly residue in position 6 increases the flexibility of this critical site more than does the Gly in position 9. These data in some way parallel the results of the cytotoxicity tests on B16-F10 transformed cells for the two analogs: [Gly9]-antamanide is cytotoxic after 48 h exposure, whereas [Gly6]-antamanide is almost inactive. On the contrary, both analogs are practically inactive in vivo against phalloidin.
Amodeo
P
P
Istituto per la Chimica di Molecole di Interesse Biologico, Consiglio Nazionale delle Ricerche, Arco Felice, Italy.
Saviano
G
G
Borin
G
G
Calderan
A
A
Ruzza
P
P
Tancredi
T
T
D019943:Amino Acid Substitution; D005998:Glycine / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation; D012964:Sodium / Q000737:chemistry*; D012996:Solutions; D014961:X-Ray Diffraction
D010456:Peptides, Cyclic; D012996:Solutions; C100265:antamanide; D012964:Sodium; D005998:Glycine