polyDglutaminsäureKapsel

Poly-D-glutamic acid (PDGA) is a polymer consisting entirely of D-glutamic acid residues connected by gamma-peptide bonds. In nature PDGA occurs as the capsule of some Bacillus species, most notably Bacillus anthracis, where it forms a protective outer layer that surrounds the cell.

Structure and properties: PDGA is an anionic, hydrophilic polymer whose chain length can vary from thousands to tens of thousands of Daltons. The D-stereochemistry and gamma-linkages make the polymer highly resistant to proteases and phagocytosed immune components, contributing to its biological function as a capsule.

Biosynthesis and genetics: In B. anthracis, capsule biosynthesis is encoded on the pXO2 plasmid by the capBCADE gene cluster. CapB and CapC are believed to mediate polymerization of the PDGA chain, CapA supports export, while CapD is a gamma-glutamyl transferase that anchors the capsule to the cell wall peptidoglycan.

Biological role: The PDGA capsule is a major virulence factor; it protects bacteria from phagocytosis and facilitates survival in hosts, contributing to systemic infection in animal models and influencing disease progression.

Applications and research: PDGA and related polyglutamic acids are studied as biomaterials because of their biocompatibility and biodegradability. Potential uses include hydrogels, drug delivery matrices, and tissue engineering scaffolds. Research often avoids pathogenic strains by using nonpathogenic producers or recombinant systems.