No abstract

The solution‐state conformations of eight proline‐containing peptide fragments found in human salivary proline‐rich glycoprotein (PRG) were investigated in 2 × distilled water (treated with metal ion chelating resin) using 13C‐nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy. The peptide sequences and acronyms were as follows: PRG9‐2 = NH2‐G(I)‐P(2)‐CONH2, PRG9‐3 = NH2‐G(1)‐P(2)‐P(3)‐CONH2,PRG9‐4 = NH2‐G(1)‐P(2)‐P(3)‐P(4)‐CONH2, PRG9‐5 = NH2‐G(1)‐P(2)‐P(3)‐P(4)‐H(5)‐CONH2,PRG9‐6 = NH2‐G(1)‐P(2)‐P(3)‐P(4)‐H(5)‐P(6)‐CONH2, PRG9‐7 = NH2‐G(1)‐P(2)‐P(3)‐P(4)‐H(5)‐P(6)‐G(7)‐CONH2, PRG9‐8 = NH2‐G(1)‐P(2)‐P(3)‐P(4)‐H(5)‐P(6)‐G(7)‐K(8)‐CONH2 and PRG9‐9 = NH2‐G(1)‐P(2)‐P(3)‐P(4)‐H(5)‐P(6)‐G(7)‐K(8)‐P(9)‐CONH2. Sequence‐specific resonance assignments from the 13C‐NMR spectra indicated that the trans proline isomer dominated the conformations of the peptides. CD results clearly showed the presence of the poly‐l‐proline II helix as the major conformation in PRG9‐3 → PRG9‐5, supplemented by β‐ and/or γ‐turns in PRG9‐6 → PRG9‐9. These data suggest that in “metal free” water, native PRG could contain several small poly‐l‐proline II helices along with β‐ and/or γ‐turns. Since proline is the major amino acid present in native PRG, these localized conformations may contribute to PRG's global conformation and act as a primary force in determining its biological activities.