Unfolded proteins characteristics

Before discussing the ROA band signatures and general spectral characteristics of the disordered types of structure found in unfolded proteins, it is helpful to review the ROA band signatures of cc-helix and /1-sheet together with those of loops, turns, and side chains, as shown by folded proteins containing significant amounts of extended secondary structure in order to demonstrate that ROA is able to discriminate adequately between ordered and disordered polypeptide sequences. Typical... 

Raman optical activity has proved valuable in recent studies of the structure and behavior of a number of natively unfolded proteins found in quite different biological situations. Although completely unfolded, the structures appear to be more stable than those generated by complete unfolding of proteins having a tertiary fold in their native states. Such natively unfolded proteins clearly have special characteristics built into their amino acid sequences that prevent aggregation under normal physiological conditions. 

The Up Ug reactions in unfolded proteins have properties that are characteristic of prolyl peptide bond isomerizations in small peptides. The equilibrium is independent of temperature (Schmid, 1982) and independent of the concentration of additives, such as guanidinium chloride (GdmCl) (Schmid and Baldwin, 1979), that strongly decrease protein stability but do not affect prolyl peptide bond isomerization. The reaction is catalyzed by strong acid and it shows an activation energy of 88 kj/ mol, as expected for prolyl isomerization (Schmid and Baldwin, 1978). 

The overall dispersion of the signals seen in ID is an important attribute of the structural characteristics of a protein. Well-structured proteins display signals over large spectral regions whereas resonances of unstructured or unfolded proteins lump together and have values similar to that found in short (random coil) pep-... 

In the crowded cell, chaperones help prevent partly folded proteins from interfering with proper folding. Once a protein is folded and ready to go to work, the chaperone leaves and finds another unfolded protein to protect. Chaperones can also react with misfolded intermediates and restart their folding process from the beginning. It is the chaperone that guides the sequence of amino acids to develop into the three-dimensional stmcture characteristic of normal biological functions. 

Folded proteins can be caused to spontaneously unfold upon being exposed to chaotropic agents, such as urea or guanidine hydrochloride (Gdn), or to elevated temperature (thermal denaturation). As solution conditions are changed by addition of denaturant, the mole fraction of denatured protein increases from a minimum of zero to a maximum of 1.0 in a characteristic unfolding isotherm (Fig. 7a). From a plot such as Figure 7a one can determine the concentration of denaturant, or the temperature in the case of thermal denaturation, required to achieve half maximal unfolding, ie, where... 

There is a continuing interest to improve and extend the fimctional properties range of dairy proteins to provide both health benefits and their characteristic physical behaviors under different temperature, moisture, and pH conditions so that they may be included in foods that ordinarily do not contain them. One such research area is the extrusion texturization of whey proteins, which have resulted in dairy proteins with new characteristics imparted by a controlled texturization process, depending on the application desired (Hale et al., 2002 Manoi and Rizvi, 2008 Onwulata, 2009 Onwulata et al., 1998). Protein texturization is a two-step process that involves, first, the unfolding of the globular structure (denaturation) and, second, the alignments of the partially unfolded structures in the direction of mass flow in the extruder. The surface characteristics are imparted at the extruder die as the molten mass exits (Onwulata et al., 2003a). 

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