Proteins tertiary structural changes

Vigano, C., Manciu, L., Buyse, F., Goormaghtigh, E., Ruysschaert, J.M. (2000). Attenuated total reflection IR spectroscopy as a tool to investigate the structure, orientation and tertiary structure changes in peptides and membrane proteins. Biopolymers, 55(5), 373-380. 

The possibilities of application of far-UV circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy in analysis of thermal stability of proteins and structural changes within protein molecules as well in explanation of cross reactivity between food allergens have been described in more detail in Section 3.4. Likewise nuclear magnetic resonance (NMR), especially 2D and multidimensional NMR as well as the method based on diffraction of monochromatic x-rays widely used in examination of tertiary structures of allergens have been described in Section 3.4 and by Neudecker et al. (2001) and Schirmer et al. (2005). 

Different arrangements of the data from these experiments have allowed the study of several aspects linked to protein folding, namely (a) changes in the protein secondary structure, (b) changes in the protein tertiary structure, and (c) global mechanistic and structural description of the protein-folding process. The results obtained are briefly presented in the following subsections. 

FIGURE 11.15 Resolution of the protein folding of a-apolactalbumin. (a) Detection of changes in protein secondary structure (far-UV circular dichroism measurements), (b) Detection of changes in protein tertiary structure (near-UV circular dichroism measurements), (c) Complete description of protein folding. Resolution of the row-wise data set formed by near-UV (Dj) and far-UV (D2) circular dichroism measurements. Solid line native conformation, dash-dotted line intermediate conformation, dotted line unfolded conformation. 

All the constituent amino acid sidechains in proteins are susceptible to attack by oxidants and free radicals, but some are more vulnerable than others. Thus, exposure of proteins to free radical-generating systems may induce tertiary structural changes as a consequence of modifications to individual amino acid sidechains. As secondary structure is stabilised by hydrogen bonding between peptide groups, interactions of radical species with the polypeptide backbone and interference with the functional groups of the peptide bonds may cause secondary structural modifications. Disruption of the secondary structure may also occur under certain conditions of free radical attack at the a-carbon atom of the peptide bond [20],... 

R571 C. Vigano, L. Manciu, F. Buyse, E, Goormaghtigh and J.-M. Ruysschaert, Attenuated Total Reflection IR Spectroscopy as a Tool to Investigate the Structure, Orientation and Tertiary Structure Changes in Peptides and Membrane Proteins , Biopolymers, 2001, 55, 373... 

It has been observed for several proteins that the intermediate structures are formed as the protein unfolds from N state to D state [26]. As the protein unfolds, protein loses tertiary structure and, frequently, secondary structure. In some instances, the secondary structure remains intact while the tertiary structure is lost [12], which is clear from spectral studies that measure loss of secondary and tertiary structural changes. One spectroscopic technique that is sensitive to tertiary structure (e.g., fluorescence) would detect changes, whereas other techniques that are sensitive to secondary structures (e.g., far UV CD) do not show any spectral changes. This molecular property is defined as molten globule or structured intermediate [12]. These intermediates expose hydrophobic domains, and thus promote aggregation or surface adsorption. 

Changes in amino acid sequence of proteins (primary structure). Changes in protein function, measured directly by determining enzyme activity or antigenicity (secondary and tertiary structure). ... 

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