CONFORMATIONAL AND DYNAMIC PROPERTIES OF A 14-RESIDUE ANTIFREEZE GLYCOPEPTIDE FROM ANTARCTIC COD

The H-1 and C-13 NMR spectra of a 14-residue antifreeze glycopeptide f rom Antarctic cod (Tetramatomus borchgrevinki) containing two proline residues have been assigned. C-13 NMR relaxation experiments indicate motional anisotropy of the peptide with a tumbling time in water at 5 degrees C of 3-4 ns. The relaxation data and lack of long-range NOEs a re consistent with a linear peptide undergoing significant segmental m otion. However, extreme values of some coupling constants and strong s equential NOEs indicate regions of local order, which are most evident at the two ATPA subsequences. Similar spectroscopic properties were o bserved in the 16-residue analogue containing an Arg-Ala dipeptide add ed to the C-terminus. Molecular modeling also showed no evidence of lo ng-range order, but the two ATPA subsequences were relatively well det ermined by the experimental data. These motifs were quite distinct fro m helical structures or beta turns commonly found in proteins, but rat her resemble sections of an extended polyproline helix. Thus, the NMR data provide a description of the local order, which is of relevance t o the mechanism of action of the antifreeze activity of the antifreeze glycopeptides as well as their ability to protect cells during hypoth ermic storage.