X-ray structures of aza-proline-containing peptides

Area of Science:

• Biochemistry
• Structural Biology
• Peptide Chemistry

Background:

• The aza-analogue of proline (AzPro) is a proline analog with a nitrogen atom replacing the alpha-carbon.
• Understanding AzPro's structural impact is crucial for peptide design and function.

Purpose of the Study:

• To elucidate the structural properties of the aza-analogue of proline (AzPro) within peptide structures.
• To compare the folding tendencies of AzPro-containing peptides with those of proline-containing peptides.

Main Methods:

• X-ray crystallography was used to determine the structures of seven AzPro-containing peptides.
• Analysis of ten AzPro motifs to identify key structural features.

Main Results:

• AzPro residues exhibit non-planar nitrogen atoms due to steric hindrance.
• AzPro-adjacent amide groups show reduced electronic conjugation, leading to longer amide bonds.
• The proton-accepting character of pyrazolidine nitrogens is weak.
• Absolute configuration of AzPro nitrogens is sequence-dependent.
• AzPro assumes a consistent three-dimensional structure across different sequences.

Conclusions:

• AzPro possesses distinct structural characteristics compared to proline.
• AzPro induces folding tendencies that oppose those of proline, offering new possibilities for peptide structure modulation.