Globular proteins electrostatic interactions

The main contributions to AadsG for a globular protein are from electrostatic, dispersion, and hydrophobic forces and from changes in the structure of the protein molecule. Although in this section these contributions are discussed individually, strict separation of the influence of these forces on the overall adsorption process of a protein is not possible. For instance, adsorption-induced alteration of the protein structure affects the electrostatic and hydrophobic interaction between the protein and the surface. When the sorbent surface is not smooth but is covered with (polymeric)... 

Another property of proteins which is important in the understanding of the limits of their catalytic activity, as well as being useful in their recovery, is solubility. The solubility of globular proteins in aqueous solution is enhanced by weak ionic interactions, including hydrogen bonding between solute molecules and water. Therefore, any factor which interferes with this process must influence solubility. Electrostatic interactions between protein molecules will also affect solubility, since repulsive forces will hinder the formation of insoluble aggregates08. ... 

Even extremophilic organisms and their proteins contain the same 20 amino acids with bonds similar to those in mesophiles. As the difference in free enthalpy between folded and unfolded states of globular proteins AG N >G is only about 45 15 kj mol-1 the sequence and structure of extremophilic proteins should differ from those of ordinary species. However, the main question, namely which properties cause the increase in denaturation temperature of thermostable proteins, is still debated (Rehaber, 1992). Theoretical and experimental analyses have shown that thermal stability is largely achieved by small but relevant changes at different locations in the structure involving electrostatic interactions and hydro-phobic effects (Karshikoff, 2001). There is no evidence for a common determinant or for just one effect causing thermostability. 

Real proteins are built up both from hydrophobic and polar amino acid residues, some of the latter can be charged. Many of the conformational and collective properties of proteins are due to a complex interplay between short-range (hydrophobic) effects and long-range (Coulomb) interactions. Electrostatic effects can also determine some of the unique solution properties of globular proteins. We have already discussed the results of simulations... 

How then can we account for the high degree of internal order routinely found within globular proteins We believe that combinations of the wide variety of electrostatic interactions reviewed above determine the precise three-dimensional structure of the interior of a protein. We argue that the sum of these interactions produces, at least in part, the enthalpy change on protein folding that is independent of the hydrophobic effect. Crystal structures of small organic compounds provide a useful model of protein interiors, and we now discuss some recent theoretical studies of these systems. 

S. K. Burley and G. A. Petsko cover the field of noncovalent interactions of proteins, with particular emphasis on weakly polar interactions. Their presentation of the whole field of electrostatic interactions should be of value to many workers in protein chemistry, but their special concern is with the weaker, but very important, interactions involving aromatic side chains, their orientation relative to one another, to oxygen and sulfur atoms, to amino groups, and to aromatic ligands that may bind to the protein. These interactions, only recently recognized for their influence on protein structure, play an important part in the formation of aromatic clusters in the interior of globular proteins and in other features of structure. The authors provide numerous illustrations of the principles involved, from recently determined structures, of both small molecules and proteins. 

Rogers N (1986) The modelling of the electrostatic interactions in the function of globular proteins, Prog Biophys Mol Biol, 48 37-66... 

M. Vasquez, M. R. Pincus, and H. A. Scheraga, Biopolymers, 26, 351 (1987). Helix-Coil Transition Theory Including Long-Range Electrostatic Interactions Application to Globular Proteins. 

A typical structure of a water-soluble globular protein consists of hydrophilic amino acid residues outside and hydrophobic ones inside. The hydrophobic environments support various electrostatic interactions within the protein, which plays a crucial role in the enzymatic reaction. Therefore, a simple model complex involving such electrostatic interactions must have hydrophobic environments around the active site such that they are not much influenced by an external effect of solvent. It follows that the models must to some extent be examined in a nonpolar solvent in order to mimic the behavior of native ones. 

The performance of protein or antibody microarrays is dependent on various factors. One of these is the use of an appropriate microarray surface for the immobilization of the protein or antibody samples. Most conventional microarray surfaces have been adapted from DNA chip technology. DNA can easily be immobilized by electrostatic interactions of the phosphate backbone onto a positively charged surface. In contrast to DNA, as already mentioned, proteins are chemically and structurally much more complex and show variable charges, which may influence the efficiency of protein attachment. Additionally, proteins lose their structure and biochemical activity easily. For example, globular proteins consist of a hydrophilic exterior and a hydrophobic interior. When immobilized on a hydrophobic surface, the inside of the protein turns out, which may destabilize the structure and, simultaneously, the activity of the protein. These considerations demonstrate the complex requirements for protein immobilization. 

In their native conformation, globular proteins have non-polar amino acid side chains oriented towards the interior of the protein and polar side chains oriented outwards, towards the solvent. The stability of the native conformation is determined by hydrophobic interactions within the interior of the molecule, and electrostatic interactions and hydrogen bond interactions at the protein-water interface. Disturbing these interactions can alter the balance between the intra- and intermole-cular interactions, which are responsible for maintaining the protein in soluble... 

N. K. Rogers and M. J. E. Sternberg,/. Mol. Biol., 174,527 (1984). Electrostatic Interactions in Globular Proteins. Different Dielectric Models Applied to the Packing of a-Helices. 

N. K. Rogers, Progr. Biophys. Mol. Biol., 48, 37 (1986). The Modeling of Electrostatic Interactions in the Function of Globular Proteins. 

The cell membrane is associated with intrinsic and extrinsic proteins. Intrinsic proteins are globular proteins that generally span the bilayer and are held within the membrane by hydrophobic and electrostatic interactions. The proteins can form channels, carriers, or pumps that enable polar molecules to cross the membrane. 

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