Hydration protein glasses

Usha and Wittebort (1989) studied the NMR of crystalline cram-bin. At 140 K the protein hydrate is stationary, with t = 1 msec. Above 200 K changes in the signal with temperature are consistent with a glass transition or melting of the hydration water. This broad transition parallels closely the changes with temperature found for the heat capacity, Mossbauer spectroscopic, and other properties of hydrated protein crystals. At room temperature no more than 12 water molecules are orien-tationally ordered. The average rotational correlation time of the hydration water is about 40 times longer than that for bulk water. 

Toumier, A.L., Xu, J., and Smith, J.C. Translational hydration water dynamics drives the protein glass transition, Biophys.., 85,1871, 2003. 

Compared to natively folded proteins, compact denatured states ( MGs ) experience a modest increase in the number of water molecules in the hydration layer, and a slightly smaller perturbation of hydration water dynamics. Soluble protein-water dynamical coupling has been elucidated by simultaneous examination of transitions in protein and water dynamics as a function of temperature. Hydrated proteins at room temperature exhibit liquid-like motion on the subnanosecond timescale and behave like glasses at low temperature. The dynamical (or glass) transition between the low-temperature glassy state and room-temperature liquid-like state plays an important role in energy flow processes in proteins (see Ref [86] and Chapters 7 and 11). 

Protein-glass transition and hydration-layer dynamics... 

One way to understand the protein hydration layer is to go to the low-temperature limit so that the dynamics slows down and one can hopefully discern different types of motion. Such studies have been carried out, both by experiments and by simulations. Neutron-scattering experiments show a sharp change in the molecular motions of a hydrated protein around 220 K, which has been attributed to a glass transition in the protein. The change is measured in the mean-square displacements of the protein atoms. The mean-square displacement shows a rapid increase as the temperature is increased beyond 220 K (see Figure 6.3)[7]. 

Biological activity is found to be restored after the protein-glass transition [8]. The protein-glass transition appears to be a general phenomenon at low temperature in hydrated proteins. 

A low-tcmpcraturc, dynamically driven structural transition observed in a polypeptide by solid-state NMR spectroscopy has been reported by Bajaj et At low temperatures, proteins and other biomolecules are generally found to exhibit dynamic as well as structural transitions. This includes a so-called protein glass transition that is universally observed in systems cooled between 200 and 230 K, and which is generally attributed to interactions between hydrating solvent molecules and protein side chains. However, there is also experimental and theoretical evidence for a low-temperature transition in the intrinsic dynamics of the protein itself, absent any solvent. In the study by Bajaj et al., low-temperature solid-state NMR was used to examine site-specific fluctuations in atomic structure and dynamics in the absence of solvents. In particular, they employed MAS NMR to examine a structural phase transition associated with dynamic processes in a solvent-free polypeptide lattice at temperatures as low as 90 K. Several quantitative solid-state NMR experiments were employed to provide site-specific measurements of structural and motional features of the observed transition. 

R. B. Gregory, Protein hydration and glass transitions, in D. Reid (Ed.), The Properties of Water in Foods Isopow 6 Kluwer Academic 1997. 

Membranes such as NC supported on glass may be more applicable for protein microarrays than glass substrates. Supported charged nylon membranes for microarrays are currently entering the marketplace as well. The essential ingredient for protein is water. Protein hydration reduces the likelihood for surface denaturation. Hydrophilic membranes allow proteins to... 

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