NMR and X-ray crystallographic studies on cyclic tetrapeptide, cyclo (D-Phe-Pro-Sar-Gly)

Area of Science:

• Biochemistry
• Structural Biology
• Peptide Chemistry

Background:

• Cyclic peptides are important in drug discovery and biological processes.
• Understanding peptide conformation is crucial for predicting function and interactions.
• Synthetic cyclic tetrapeptides offer a model system for conformational studies.

Purpose of the Study:

• To elucidate the solution and crystal conformations of the synthetic cyclic tetrapeptide cyclo(D-Phe-Pro-Sar-Gly).
• To compare conformational behavior in different states (solution vs. crystal).
• To investigate the presence and role of intramolecular hydrogen bonds.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy for solution state analysis.
• X-ray crystallography for crystal state structure determination.
• Analysis of peptide bond configurations (cis/trans) and structural parameters.

Main Results:

• Two distinct conformations were identified in solution: cis-trans-cis-trans and trans-cis-trans-cis peptide bonds.
• No intramolecular hydrogen bonds were observed in either solution conformer.
• X-ray diffraction revealed an orthorhombic crystal structure (space group P2(1)2(1)2(1)) with a single cis-trans-cis-trans conformer, consistent with solution conformer 1.

Conclusions:

• The synthetic cyclic tetrapeptide cyclo(D-Phe-Pro-Sar-Gly) exhibits conformational flexibility in solution.
• The crystal structure represents one of the predominant solution conformations.
• Conformational preferences are influenced by the peptide sequence and the surrounding environment (solution vs. crystal).