Characterization of an L-α,β-diaminopropionic acid polymer with comb-like structure isolated from a poly(ε-L-lysine)-producing Streptomyces sp.

Polymers of basic amino acids function as polycationic compounds under physiological conditions and exhibit intriguing biological properties, such as antimicrobial and antiviral activities, immunopotentiating ability, and DNA-binding activity. Poly(epsilon-l-lysine) (epsilon-PL) produced by some strains of Streptomyces spp. is a cationic homopolymer of l-lysine linking between epsilon-amino and alpha-carboxylic acid functional groups and has been used as a food preservative based on its biocompatibility and biodegradability. An epsilon-PL-producing strain of Streptomyces sp. USE-33 was found to secrete a novel polycationic substance into its culture broth along with epsilon-PL. High-performance liquid chromatography analyses and one- and two-dimensional H-1 and C-13 nuclear magnetic resonance (NMR) experiments, accompanied by NMR titration studies, revealed that the secreted substance was poly[beta-(l-diaminopropionyl-l-diaminopropionic acid)], PAP, characterized by an isopeptide backbone linking between the beta-amino and alpha-carboxylic acid groups of l-alpha,beta-diaminopropionic acid (l-Dpr) with pendent l-Dpr residues. PAP had a molecular weight of 500 to 1400, and copolymers composed of the two amino acids l-Dpr and l-lysine were not detected in the producer strain USE-33. The strain coproduced high levels of the two poly(amino acid)s in the presence of glycerol, citrate, and ammonium sulfate at pH 4.0 in a two-stage cultivation procedure. PAP exhibited strong inhibitory activities against several yeasts and weaker activities against bacteria than epsilon-PL. PAP may share a number of biological functions with epsilon-PL, and the use of PAP along with epsilon-PL has potential as a specific and advanced material for technical applications in various fields.

Automated summary

Polymers of basic amino acids function as polycationic compounds with various biological properties under physiological conditions, such as antimicrobial and antiviral activities, immunopotentiating ability, and DNA-binding activity. The ε-PL and PAP produced by some Streptomyces strains have potential as food preservatives and inhibitors with wide applications in various fields.