Abstract
Natural abundance 13C NMR spectroscopy (at 67.9 MHz) is used to study an aqueous solution of the antifreeze glycoproteins 3 to 6 from the Antarctic cod. Assignments of resonances to specific carbons of the known Ala-Ala-[beta Gal-(1 leads to 3)-alpha-N-acetylgalactosamine]Thr repeating unit are presented. Some of the carbons of the proline residues of glycoprotein 6 are also identified. Spin-lattice relaxation times (at 30 degrees C), linewidths (at 35 degrees C), nuclear Overhauser enhancements (at 35 degrees C), and the temperature dependence of chemical shifts (from 0 degrees to 75 degrees C) all strongly suggest that these antifreeze glycoproteins are predominantly or entirely flexible random coil polymers.
Highlights
Nuclear Magnetic Resonance Spectroscopy of Antifreeze established that the prolines replace some of the alanines which follow threonine residues in the sequence [11, 12]
Arthur L.DeVries ielastic light scattering results were interpreted as showing a coil that is somewhat lessflexible and extended thaanrandom coil [15]
We present some preliminary "'C NMR
Summary
Enough relative to the TI values of all carbons to yield equi- model compound for C"of the glycosylated threonines, and librium intensities in Fig. lA.The spectrumof Fig. 1Bresulted a-D-GalNAc is not a good model compound for C-1and C-3of after 131,072scans with a recycle time of 1s (total time, h). We show that thefour strongest minor resonances (indi- residue [24], only Peaks 7 and 8 have chemical shifts consistcated by their chemical shifts in Fig. 1B) can be assigned to ent with assignmentstothe 0-glycosidicallylinked C" of. C",C", and Cyof a proline residue and to C"of a threonine threonine and C-3of a-GalNAc [22, 23, 27].
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