title: A solid-state NMR study of protein hydration and stability.
abstract: OBJECTIVE
  The mobility of protein in powders at different hydration levels was studied in relation to aggregation and activity.
  
  
  METHODS
  Magic angle spinning 13C, 15N, 1H, 2H, and 17O NMR techniques were used to determine changes in the mobility of surface residues in proteins as a function of hydration and related to changes in activity. NMR relaxation measurements of high frequency (omega0, T1) and low frequency (omega1,T1p) motions have been carried out on lyophilized DNase, insulin and lysozyme stored at different relative humidities. Moisture-induced aggregation and enzymatic activity of the lyophilized proteins was determined by high performance size exclusion chromatography and bioassays.
  
  
  RESULTS
  There was little change in T1p observed with increasing humidity. The results show, however, that there is a decrease in T1 for DNase, insulin and lysozyme at relative humidities ranging from 0-98%, and we propose that the reduction in T1 is related to the aggregation susceptibility of proteins during storage at different humidities. The water mobility was determined directly using 17O NMR experiments. We found that as the amount of weakly-bound water increases, the protein surface mobility decreases and is coupled with increased aggregation. Aggregation measurements at different humidities were correlated with bioassays for lysozyme and found to be consistent with the hydration data.
  
  
  CONCLUSIONS
  Mobility of protein molecules was determined by solid-state NMR over a wide range of % RH and it was found that water content leads to a change in mobility of protein molecules. The aggregation and activity of proteins were strongly correlated to change in molecular mobility.
authors.affiliation: School of Chemistry, University of Melbourne, Parkville, Vic, Australia. f.separovic@chemistry.unimelb.edu.au
authors.forename: F
authors.initials: F
authors.lastname: Separovic
authors.forename: Y H
authors.initials: YH
authors.lastname: Lam
authors.forename: X
authors.initials: X
authors.lastname: Ke
authors.forename: H K
authors.initials: HK
authors.lastname: Chan
mesh_terms: D002247:Carbon Isotopes; D003851:Deoxyribonucleases / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D004789:Enzyme Activation; D005612:Freeze Drying; D006801:Humans; D006860:Hydrogen Bonding; D007328:Insulin / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D009113:Muramidase / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular; D010103:Oxygen Isotopes; D011485:Protein Binding; D011522:Protons; D011994:Recombinant Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D013048:Specimen Handling; D014867:Water / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D007328:Insulin; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D011522:Protons; D011994:Recombinant Proteins; D014867:Water; D003851:Deoxyribonucleases; D009113:Muramidase