Selective Metal Cation Binding of Elastomeric Protein: Two Types of Binding Sites and Elastomeric Functions

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An elastomeric protein called elastin is fully responsible for sophisticated biological elasticity in mammalian tissues such as the aortal wall, ligament, lung, and skin. A key step in elastogenesis to establish the structural basis of elastomeric function, a self assembly of the precursor protein in extracellular space, can be mimicked by the temperature-dependent coacervation of an elastin-related polypeptide-water system. Characteristics of the two types of metal cation binding sites, carboxy oxygens of side ammo acid residues and peptide backbone carbonyl oxygens, were examined in relation to the multiple biofunctionality as an extracellular matrix using biologically derived α-elastin and synthetic elastin model polypeptide. Nonspecific metal cation bibdings to the carboxy groups of side amino acid residues cause simple salting-in and -out effects. Peptide backbone carbonyl oxygens of particular repeating peptide sequence, -Val-Pro-Gly-Val-Gly-, are specifically selective to Ca2+ ions and substantially rejective of other metal cations including alkali metal cations, Mg2+, and Cu2+ ions. Ca2+ ion binding to peptide carbonyl groups of elastomeric protein induces destruction of a key structure for coacervate characteristics and elastomeric functions.
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