Mineral-binding peptides

Vegarud, G.E., Langsrud, T., and Svenning, C. 2000. Mineral-binding milk proteins and peptides occurrence, biochemical and technological characteristics. Br. J. Nutr. 84, 91-98. 

Biologically active peptides are food-derived peptides that can exhibit diverse activities, including opiate-like, mineral binding, immunomodulatory, antimicrobial, antioxidant, antithrombotic, h)q)ocholesterolemic. 

Meisel, H. and FitzGerald, R.J. Biofunctional peptides from milk proteins. Mineral binding and cyto-modulatory effects. Curr. Pharmaceut. Des. 9 1289-1295, 2003. 

Similarly to mineral-binding proteins, casein-derived phospho-peptides can form salts with minerals such as calcium due to the binding properties of the phosphoserine residue. These peptides are involved in the increased absorption and bioavaUabflity of calcium and other minerals (zinc, copper, manganese and iron)... 

There is a need to resume studies of soil saccharides and peptides. These can compose as much as 30-40% (when account is taken of the compositions of humin materials). Much is known about how polysaccharides of known structures interact with soil colloids, but it has not been possible as yet to know in sufficient detail the structures of the polysaccharides that persist in the soil. Hence we do not know the mechanisms of their binding to soil mineral colloids. The same applies for the peptide materials, though it is clear that polysaccharides and peptides have important roles in soil structure formation and stabilization. 

Bone sialoprotein, osteopontin, and osteocalcin are synthesized and deposited as the mineralization process begins and mineral nodules form (Stein and Lian, 1993). Bone sialoprotein contains the cell-adhesive arginine-glycine-aspartic acid peptide sequence and may thus mediate osteoblast adhesion on the extracellular matrix (Gehron-Robey, 1989). Osteocalcin, a calcium-binding protein, interacts with hydroxyapatite and is thought to mediate coupling of bone resorption (by osteoclasts) and bone formation (by osteoblasts and/or osteocytes) (Stein and Lian, 1993). 

In addition, peptides binding different minerals have been found in whey proteins, i.e., from (3-lg, a-la and LF. Since these proteins are not phosphorylated, the minerals seem to bind through other binding sites than caseins. Seventeen (17) different peptides have been identified by hydrolysis of (3-lg with thermolysin using two different concentrations of calcium. Also, peptides from a-la and LF using trypsin, chymotrypsin or pepsin have been reported. Studies with 3-lg and a-la peptides have shown a higher affinity for iron than the native proteins (Vegarud et al., 2000). 

Of the 25 animal phyla, almost half are worms. Thus, it is not at all surprising that some worms contain toxins. The nemertines are a phylum of over 800 known species which resemble flatworms but are active predators on crustaceans and other worms. This phylum is exceptionally toxic among the various worm phyla. The Heteronemertine side possesses peptide toxins which appear to be only defensive, as these animals have no means of injecting a venom. The peptides include neurotoxins, which enhance excitability of nerve membranes, and cytolysins, which permeabilize and destroy cell membranes. Members of the Hoplonemertine class inject a venom into their prey using a mineralized stylet located in their proboscis, which is also used to immobilize the prey. Their toxins are alkaloids similar to nicotine which in minute amounts paralyze crustaceans and annelid worms and primarily activate nicotinic acetylcholine receptors. Another well-known worm toxin is nereistoxin, a disulfide-containing alkaloid which also binds to nicotinic... 

Hydrochloric acid in the demineralizing compartment dissolves the bone mineral and denatures exposed collagen fibers for hydrolysis by cathepsin K. This lysosomal endopro-tease (Fig. 10.4a and b) has a cysteine thiol group at its catalytic center (Table 7.1 Fig. 10.4c). Cathepsin K is secreted in larger amounts than other lysosomal proteases and its specificity is due to unique amino acid residues around the peptide binding site. The enzyme hydrolyzes a) ) and a2(I) polypeptides from incompletely denatured fibers in the demineralizing compartment, leaving the cross-linked, telopeptide ends (Sect. 4.2.2). 

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