Helix‐coil stability constants for the naturally occurring amino acids in water. XXIII. Proline parameters from random poly(hydroxybutylglutamine‐CO‐L‐proline)

Publisher Website
Google Scholar
Abstract
Water‐soluble random copolymers containing L‐proline and N5‐(4‐hydroxybutyl)‐L‐glutamine were synthesized by copolymerization of the tripeptides H‐L‐Glu(OBzl)‐L‐Glu(OBzl)‐L‐Glu(OBzl)‐OH and H‐L‐Glu(OBzl)‐L‐Pro‐L‐Glu(OBzl)‐OH, using ben‐zotriazolyl‐N‐oxy‐tris(dimethylamino)‐phosphonium hexafluorophosphate as condensing reagent, and subsequent aminolysis of the Bzl ester groups with 4‐amino‐1‐butanol. These copolymers were found to contain significant amounts of N5‐(4‐hydroxybutyl)‐D‐glutamine, thus requiring the synthesis of a binary copolymer containing only D‐ and L‐N5‐(4‐hydroxybutyl)glutamine residues in order to evaluate the possible effects of the D‐residues on the conformational properties of poly(hydroxybutylglutamine‐co‐L‐proline). The different copolymers were fractionated, and their thermally induced helix‐coil transition curves were obtained in water at neutral pH. When proper corrections were applied for the helix‐destabilizing properties of N5‐(4‐hydroxybutyl)‐D‐glutamine, the Zimm‐Bragg parameters σ and s for L‐proline could be deduced from the melting curves of poly (hydroxybutylglutamine‐co‐L‐proline). The results indicate that L‐proline acts as a very strong helix breaker over the entire temperature range from 0 to 60°C.