New ice-binding face for type I antifreeze protein

AbstractType I antifreeze protein (AFP) from winter flounder is an alanine-rich, 37 amino acid, single α-helix that contains three 11 amino acid repeats (Thr-X2-Asx-X7), where X is generally Ala. The regularly spaced Thr, Asx and Leu residues lie on one face of the helix and have traditionally been thought to form hydrogen bonds and van der Waals interactions with the ice surface. Recently, substitution experiments have called into question the importance of Leu and Asn for ice-binding. Sequence alignments of five type I AFP isoforms show that Leu and Asn are not well conserved, whereas Ala residues adjacent to the Thr, at right angles to the Leu/Asn-rich face, are completely conserved. To investigate the role of these Ala residues, a series of Ala to Leu steric mutations was made at various points around the helix. All the substituted peptides were fully α-helical and remained as monomers in solution. Wild-type activity was retained in A19L and A20L. A17L, where the substitution lies adjacent to the Thr-rich face, had no detectable antifreeze activity. The nearby A21L substitution had 10% wild-type activity and demonstrated weak interactions with the ice surface. We propose a new ice-binding face for type I AFP that encompasses the conserved Ala-rich surface and adjacent Thr

Trisubstituted (E)-alkene dipeptide isosteres as β-turn promoters in the gramicidin S cyclodecapeptide scaffold

(Chemical Equation Presented) A concise synthesis of a gramicidin S analogue with trisubstituted (E)-alkene dipeptide isostere (TEADI) replacements at both D-Phe-Pro positions was realized. Conformational analysis demonstrated that TEADIs can serve as type II β-turn promoters in a cyclic scaffold and successfully mimic a proline residue. © 2006 American Chemical Society