Conformational changes in cyclic (D-Phe-Pro-Gly-D-Ala-Pro) upon complexation with Mg++.

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Biophysical Chemistry

Background:

• Cyclic peptides are important biomolecules with diverse functions.
• Metal ion complexation can significantly alter peptide structure and properties.
• Understanding metal-peptide interactions is crucial for various applications.

Purpose of the Study:

• To synthesize and characterize a novel complex between a cyclic pentapeptide and a metal ion.
• To investigate the structural and conformational changes upon complexation.
• To explore the coordination environment of the metal ion within the peptide complex.

Main Methods:

• Slow evaporation of a solution containing the cyclic pentapeptide and magnesium thiocyanate (Mg(SCN)2).
• X-ray diffraction analysis to determine the crystal structure.
• Conformational analysis of the peptide before and after complexation.

Main Results:

• Formation of a 1:1 complex between the cyclic pentapeptide and Mg++.
• The crystal structure reveals an infinite stack of alternating peptide and Mg++ moieties.
• Octahedral coordination of Mg++ involving peptide carbonyls, water molecules, and a thiocyanate (NCS-) ion.
• Significant conformational changes in the peptide, with dihedral angles (phi and psi) altering by 90 to 230 degrees.
• Oxidation of one NCS- to sulfate (HSO4-) providing the counter-ion.

Conclusions:

• This study reports the first metal ion complex with a cyclic pentapeptide.
• The complex exhibits a unique infinite stacked structure with profound conformational changes in the peptide.
• The findings provide valuable insights into metal-peptide interactions and coordination chemistry.