Structure and Function of Macromolecular Antifreezes (Peptide, Glycopeptide, Fish)
Schrag, Joseph D.
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Permalink
https://hdl.handle.net/2142/71434
Description
Title
Structure and Function of Macromolecular Antifreezes (Peptide, Glycopeptide, Fish)
Author(s)
Schrag, Joseph D.
Issue Date
1984
Department of Study
Physiology and Biophysics
Discipline
Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Biochemistry
Abstract
Many polar fishes are protected from freezing by peptide or glycopeptide antifreezes which inhibit ice growth. The relationship between the structures of these molecules and the mechanism by which they work in investigated in this thesis.
Glycopeptide antifreezes range in molecular weight from 2600-33,000 daltons and most are polymers of the tripeptide ala-ala-thr. Each threonine is glycosidically linked to the disaccharide galactose-N-acetylgalactosamine. The glycopeptide antifreezes from Microgadus tomcod and Eleginus gracilis are unique, however, in that they contain arginine. Determination of the amino acid sequences of these antifreezes indicates that glycopeptide antifreeze structure is highly conserved. Arginine occasionally replaces the glycosidically linked threonine in these sequences, but the basic tripeptide repeat is otherwise maintained.
The large glycopeptides are more efficient inhibitors of ice growth than are the small proline containing glycopeptides. Although the secondary structures of the glycopeptides are uncertain, some investigators have proposed some ordered structures and have suggested that the proline residues of the small glycopeptides may disrupt this structure and reduce their effectiveness. The results presented in this study, however, indicate that the observed differences in effectiveness between different sizes of glycopeptide antifreezes can be attributed entirely to differences in molecular size rather than differences in conformation.
A model of peptide antifreeze function is based on the structure of the winter flounder peptide. Polar amino acids are periodically spaced in this peptide and the spacing of the polar residues in a helical conformation is presumed to allow efficient hydrogen bonding of the antifreeze of the ice surface. Some investigators predicted that all peptide antifreezes would be similarly arranged. Peptide antifreezes were isolated from the zoarcids Rhigophila dearborni and Lycodes polaris. No periodic placement of polar groups is evident in the amino acid sequences and CD indicates little or no helical structure in these peptides. The secondary structure of these peptides remains uncertain, but a large amount of (beta)-structure is predicted from the amino acid sequences. Peptide antifreeze structures clearly show substantial variation.
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