Biopolymer stability conformations

Fig. 7. Besides direct interactions between functional groups of the biopolymer molecule itself there are also various kinds of interactions with water molecules. These hydrophilic and hydrophobic interactions are essential for stabilizing the native conformation of biopolymers. In the last few years some progress was made in elucidating the hydration of these molecules.

Cross-linking constrains the conformational flexibility of biopolymers and, as a rule, stabilizes their secondary, tertiary, and quaternary structures against the denaturing effects of high temperatures.29 We used differential scanning calorimetry (DSC) to compare the heat-induced conformational transitions of selected RNase A samples that were characterized in Figure 15.2. A brief introduction to DSC is provided in Section 15.15.1 for those readers unfamiliar with this biophysical method. Trace 1 in Figure 15.3a is the heat absorption... 

Nevertheless, in view of the fact that the stability of biopolymers, in respect of their secondary and tertiary (conformational) structure, is strongly influenced by interactions with structural H2O (45), it is of considerable interest to explore further the features discussed in the penultimate paragraph. Even for a totally collision-broadened (relaxation-type) initial step... 

With larger biopolymers, the solvent of choice is an aqueous medium since, in most cases, water is required to maintain the native conformation in solution. In addition, the exchangeable protons are of importance because they are involved in such things as hydrogen bonding and salt bridges, which are critical in stabilizing the native structure. The total spectrum... 

H. Meirovitch, M. Vasquez and H. A. Scheraga, Biopolymers, 26, 651 (1987). Stability of Polypeptide Conformational States as Determined by Computer Simulation of the Free Energy. 

Substrate selectivity and stereoselectivity of enzyme catalysis are known to be influenced by the reaction media. As has been mentioned in the preceding section, a profound feature of the behaviour of enzymes in an anhydrous organic medium is the conformational stability, which leads to enhanced thermal stability and the ligand memory property. These features of enzymes have been exploited to impart novel catalytic characteristics that are absent in the native biopolymers. 

The second fundamental aspect of the recent developments that we shall examine is the conformational one. As is well known, the activity of biological molecules and, in particular, of biopolymers is frequently strongly dependent upon their conformation. The understanding of the factors governing conformational stability of biomolecules and the evalution of the preferred conformers is therefore of utmost interest for the further development and broadening of quantum biochemistry. It is one of the major contributions of the all-valence electrons methods to have made this development feasible. 

These interactions are frequently ionic in character. The coulombic forces of interaction between macroions and lower molecular weight ionic species are central to the life processes of the cell. For example, intermolecular interactions of nucleic acids with proteins and small ions, of proteins with anionic lipids and surfactants and with the ionic substrates of enzyme catalyzed reactions, and of ionic polysaccharides with a variety of inorganic cations are all improtant natural processes. Intramolecular coulombic interactions are also important for determining the shape and stability of biopolymer structures, the biological function of which frequently depends intimately on the conformational features of the molecule. 

A. A. Rashin, Biopolymers, 23, 1605 (1984). Buried Surface Area, Conformational Entropy, and Protein Stability. 

Dialkylamino acids, C -dialkylamino acids, amino acids bearing two alkyl substituents at the a-carbon atom. Examples are the naturally occurring amino acids diethylglycine (Deg), a-aminoisobutyric acid (Aib), or isovaline (Iva, 2-amino-2-methylbutyric acid). Such amino acids are often incorporated into peptides to study the conformational requirements of receptors, and are used as building blocks for the stabilization of short peptides in a well-defined conformation, depending on the nature of the two substituents attached to the C -carbon. 3io-Hdices are stabilized by the incorporation of Aib and other C -dialkyl-substituted building blocks [P. Balaram, T. S. Sudha, Int.J. Pept. Protein Res. 1983, 21, 381 I. L. Karle, Biopolymers 1996, 40,157 B. Pispisa et al.. Biopolymers 2000, 53,169]. 

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