Conformational study of the basic proline-rich polypeptides from human parotid saliva

Area of Science:

• Biochemistry
• Structural Biology
• Spectroscopy

Background:

• Human parotid saliva contains basic proline-rich polypeptides P--D and P--E.
• These polypeptides possess known primary amino acid structures.
• Previous studies have not fully elucidated their conformational properties.

Purpose of the Study:

• To investigate the conformational characteristics of polypeptides P--D and P--E.
• To determine the secondary structure elements and stability of these salivary polypeptides.
• To explore the influence of pH on their structural integrity.

Main Methods:

• Circular Dichroism (CD) spectroscopy was employed to analyze secondary structure.
• Proton Nuclear Magnetic Resonance (1H-n.m.r.) spectroscopy provided detailed structural insights.
• Conformational analysis was performed across a pH range of 3.0 to 11.0.

Main Results:

• CD spectra revealed unique conformational features for P--D (trough at 202 nm) and P--E (trough at 201 nm).
• A fragment of P--D with five consecutive prolyl residues showed a trough at 204 nm, suggesting a poly-L-proline II-like conformation.
• No significant changes in CD or 1H-n.m.r. spectra were observed between pH 3.0 and 11.0.

Conclusions:

• Polypeptides P--D and P--E adopt distinct conformations, differing from the canonical poly-L-proline II structure.
• The presence of consecutive prolyl residues may contribute to a poly-L-proline II-like conformation in P--D.
• The structural stability of P--D and P--E across a broad pH range indicates a lack of pH-sensitive ionic interactions influencing their folding.