title: Evidence for a gamma-turn motif in antifreeze glycopeptides.
abstract: Knowledge of the secondary structure of antifreeze peptides (AFPs) and glycopeptides (AFGPs) is crucial to understanding the mechanism by which these molecules inhibit ice crystal growth. A polyproline type II helix is perhaps the most widely accepted conformation for active AFGPs; however, random coil and alpha-helix conformations have also been proposed. In this report we present vibrational spectroscopic evidence that the conformation of AFGPs in solution is not random, not alpha-helical, and not polyproline type II. Comparison of AFGP amide vibrational frequencies with those observed and calculated for beta and gamma-turns in other peptides strongly suggests that AFGPs contain substantial turn structure. Computer-generated molecular models were utilized to compare gamma-turn, beta-turn, and polyproline II structures. The gamma-turn motif is consistent with observed amide frequencies and results in a molecule with planar symmetry with respect to the disaccharides. This intriguing conformation may provide new insight into the unusual properties of AFGPs.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309.
authors.forename: J A
authors.initials: JA
authors.lastname: Drewes
authors.forename: K L
authors.initials: KL
authors.lastname: Rowlen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D021301:Antifreeze Proteins; D055592:Biophysical Phenomena; D001703:Biophysics; D002240:Carbohydrate Sequence; D005399:Fishes; D005615:Freezing; D006023:Glycoproteins / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman
chemical_list: D021301:Antifreeze Proteins; D006023:Glycoproteins