polyDglutamic

polyDglutamic, or poly-D-glutamic acid, is a polymer composed of D-glutamic acid residues linked by gamma-peptide (gamma-glutamyl) bonds. It occurs in nature mainly as poly-gamma-glutamic acid (γ-PGA) produced by certain Bacillus species and is notable for its D- configuration, which confers resistance to standard proteases.

The repeating unit is D-Glu, linked through a gamma linkage rather than the conventional alpha peptide bond. The polymer can be homo- or hetero-polymeric with varying degrees of polymerization. The carboxylate groups render the molecule highly anionic at neutral pH, and the molecular weight can vary widely, influencing solubility and rheological properties.

Biosynthesis and natural occurrence: γ-PGA is synthesized by a membrane-associated enzyme complex encoded by the pgsBCA gene cluster in many Bacillus strains. The polymer is typically secreted into the extracellular medium. In Bacillus anthracis, the capsule is composed of poly-D-glutamic acid and serves as a major virulence factor by helping the bacteria evade phagocytosis and other immune defenses.

Applications and properties: PDGA is biodegradable and typically highly hydrophilic, forming viscous solutions or gels under appropriate conditions. It has been explored as a biocompatible material for drug delivery systems, wound dressings, hydrogels, and cosmetic/pharmaceutical excipients. Its multiple carboxylate groups enable metal ion chelation and it can function as a thickener or stabilizer in certain foods and industrial processes.

Safety and regulation: PDGA produced by non-pathogenic Bacillus strains is used in various industries, but the PDGA capsule of Bacillus anthracis underscores potential virulence considerations. Production and use are governed by biosafety and regulatory frameworks to mitigate risk.