Proline, which abbreviates to the 3-letter Pro or single letter P, is one of the 20 amino acids that make up proteins in our body. Proline’s R-group is unique in that it bends backwards on itself to connect with the amino group attached to the core or alpha carbon. This forms a 5-sided ring-shaped R-group incorporating the nitrogen of this amino group. Due to the rigid, ring-shape of this R-group, proline causes kinks in any polypeptide chains that include it. Proline is also a non-polar, hydrophobic amino acid, with a neutral charge at physiological pH.

Key Points

  • Proline
    • Abbreviations
      • Pro, P
    • Chemical Structure
    • R-Group: 4-C chain forms 5-membered ring with nitrogen of amino group
      • Hydrogen of nitrogen unaccessible for forming H-bonds in polypeptide chains
      • Kinks polypeptide chain
        • Conformational rigidity of amino group in amide bond connecting amino acids in polypeptide chain causes bends
        • Disrupts secondary structures like alpha-helices or beta-pleated sheets (rarely occurs in those structures)
        • Often found in joining regions between secondary structures
    • Polarity
      • Nonpolar (lipid soluble/hydrophobic)
    • Charge at pH 7
      • Neutral (0)