NRPSs and amide ligases producing homopoly(amino acid)s and homooligo(amino acid)s

Microorganisms are capable of producing a wide variety of biopolymers. Homopoly(amino acid)s and homooligo(amino acid)s, which are made up of only a single type of amino acid, are relatively rare; in fact, only two homopoly(amino acid)s have been known to occur in nature: poly(ε-L-lysine) (ε-PL) and poly(γ-glutamic acid) (γ-PGA). Bacterial enzymes that produce homooligo(amino acid)s, such as L-β-lysine-, L-valine-, L-leucine-, L-isoleucine-, L-methionine-, and L-glutamic acid-oligopeptides and poly(α-l-glutamic acid) (α-PGA) have recently been identified, as well as ε-PL synthetase and γ-PGA synthetase. This article reviews the current knowledge about these unique enzymes producing homopoly(amino acid)s and homooligo(amino acid)s.