Characterization of an l-[alpha],[beta]-diaminopropionic acid polymer with comb-like structure isolated from a poly-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 .sup.1H and .sup.13C 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. Key points * Novel cationic poly(amino acid) was found in an [epsilon]-PL-producing Streptomyces species. * Thel-[alpha],[beta]-diaminopropionic acid polymer was characterized by a comb-like structure. * The novel poly(amino acid), PAP, exhibited antibacterial and antifungal activities. Graphical abstract