Protein acidic polysaccharide, interaction

Big molecules of life include the proteins, nucleic acids, polysaccharides, and a few other more exotic constrncts of nature. Generally, it is the interactions between big molecules and small ones that nnderlie really interesting things taste or smeU or the beneficial actions of drugs, for example. 

Hydrogen bonds and ionic, hydrophobic (Greek, water-fearing ), and van der Waals interactions are individually weak, but collectively they have a very significant influence on the three-dimensional structures of proteins, nucleic acids, polysaccharides, and membrane lipids. 

Fourteen chapters, each by a different author, cover (at an advanced level) the structure of water and its interactions with proteins, nucleic acids, polysaccharides, and lipids. 

At the second critical pH (pH,, ), which is usually below the protein isoelectric point, strong electrostatic interaction between positively charged protein molecules and anionic polysaccharide chains will cause soluble protein/polysaccharide complexes to aggregate into insoluble protein/polysaccharide complexes. For negatively charged weak acid-based (e.g., carboxylic acid) polysaccharides like pectin, with the decrease of pH below the pKa of the polysaccharide, protein (e.g., bovine serum albumin (BSA))/polysaccharide (e.g., pectin) insoluble complexes may dissociate into soluble complexes, or even non-interacted protein molecules and polysaccharide chains, due to the low charges of polysaccharide chains as well as the repulsion between the positively charged proteins (Dickinson 1998). 

Screw structures or helices (helix Greek = winding, convolution, spiral) are encountered in various variations in nature and technique. Propeller-shaped, helical structures play an important role in architecture, physics, astronomy and biology. Screw-shaped macromolecular skeletons of nucleic acids, proteins and polysaccharides are important structural elements in biochemistry. Their helix turns often are stabilized through hydrogen bonds, metal cations, disulfide linkages and hydrophobic interactions. 

For the construction of artificial metalloproteins, protein scaffolds should be stable, both over a wide range of pH and organic solvents, and at high temperature. In addition, crystal structures of protein scaffolds are crucial for their rational design. The proteins reported so far for the conjugation of metal complexes are listed in Fig. 1. Lysozyme (Ly) is a small enzyme that catalyzes hydrolysis of polysaccharides and is well known as a protein easily crystallized (Fig. la). Thus, lysozyme has been used as a model protein for studying interactions between metal compounds and proteins [13,14,42,43]. For example, [Ru(p-cymene)] L [Mn(CO)3l, and cisplatin are regiospecificaUy coordinated to the N = atom of His 15 in hen egg white lysozyme [14, 42, 43]. Serum albumin (SA) is one of the most abundant blood proteins, and exhibits an ability to accommodate a variety of hydrophobic compounds such as fatty acids, bilirubin, and hemin (Fig. lb). Thus, SA has been used to bind several metal complexes such as Rh(acac)(CO)2, Fe- and Mn-corroles, and Cu-phthalocyanine and the composites applied to asymmetric catalytic reactions [20, 28-30]. 

Because it is effective in removing contaminating proteins, the latter method is useful for studying biological interactions with LPS. The phenol-water technique, which was first described by Westphal and Jann (II), takes advantage of the amphopathic nature of the LPS and the solubility of the majority of bacterial proteins in phenol. Polysaccharides, mucopolysaccharides, LPSs with 0-side chains, and nucleic acids are usually soluble in aqueous solutions and insoluble in phenol. Phenol is a weak acid its dissociation constant at 18°C in water is L2 x 10 °. Mixtures of phenol and water have a high dielectric constant. These facts form the basis of a method of partition of proteins and polysaccharides and/or nucleic acids between phenol and water. Minor modifications have been made to the basic protocol described by Westphal et al. (15) and by Johnson and Perry... 

Chitosan is a polyamine with a high degree of positive charge at pH below pK, of the amine groups (p/fj 5.5-6.5). Therefore, chitosan is prone to interact readily with negatively charged substances such as proteins, anionic polysaccharides, or fatty acids. 

Summarizing, most biomineralization proteins have a multidomain structure and can often be glycosylated by hydrophilic and often acidic polysaccharides, which also can form the domains interacting with the mineral. 

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