MAGIC-ANGLE-SPINNING NMR-STUDY OF THE HYDRATION OF THE WHEAT SEED STORAGE PROTEIN OMEGA-GLIADINS

The hydration of the wheat protein omega-gliadins was investigated by carbon and proton magic angle spinning (MAS) NMR spectroscopy, The cha nges observed in the protein carbon spectrum with increasing hydration in the range 0-50% show a general mobility increase but, even at 50% hydration, a number of glutamine side-chain carbons remain relatively immobilized, The results suggest that a conformational change occurs a t about 35% hydration, giving a looser conformation, Carbon T-1 relaxa tion times reflect the general mobility increase, in the MHz frequency range, by showing an order of magnitude decrease upon hydration, No d istinction between T-1 of the backbone and glutamine side-chain carbon yls is observed, This confirms the relative rigidity of these side-cha ins even at high hydration, MAS at high spinning rates has been used p reviously to resolve the proton spectra of hydrated omega-gliadins. Re solution was further improved by using a new high-resolution MAS probe , Interpretation of the resulting protein spectrum showed that some ph enylalanine residues are considerably motionally hindered, Moreover, e vidence shows that some glutamine side-chain amino groups are inaccess ible to solvent, A structural model for hydrated omega-gliadins is adv anced involving the formation of hydrophobic pockets held by stable in termolecular and/or intramolecular hydrogen bonding between glutamine residues. The high-resolution spectra obtained using the new probe des ign permitted the use of high-resolution 2D experiments for assignment s and to investigate conformational properties, In an attempt to use p roton relaxation parameters to characterize the protein system further , it was found that, under MAS conditions, proton T-1 relaxation times are strongly dependent on spinning rate, The results indicate that gr eat care is required when interpreting proton relaxation times recorde d under MAS conditions. (C) 1997 John Wiley & Sons, Ltd.