Enantiomerically
pure amino acid derivatives could be foundational
compounds for peptide drugs. Deracemization of racemates to l-amino acid derivatives can be achieved through the reaction of evolved d-amino acid oxidase and chemical reductants, whereas deracemization
to d-amino acid derivatives has not progressed due to the
difficulty associated with the heterologous expression of l-amino acid oxidase (LAAO). In this study, we succeeded in developing
an ancestral LAAO (AncLAAO) bearing broad substrate selectivity (13 l-amino acids) and high productivity through an Escherichia coli expression system (∼50.7
mg/L). AncLAAO can be applied to perform deracemization to d-amino acids in a similar way to deracemization to l-amino
acids. In fact, full conversion (>99% ee, d-form) could
be
achieved for 16 racemates, including nine d,l-Phe
derivatives, six d,l-Trp derivatives, and a d,l-phenylglycine. Taken together, we believe that
AncLAAO could be a key enzyme to obtain optically pure d-amino
acid derivatives in the future.
Amino-group carrier proteins (AmCPs) mediate the biosynthesis of lysine and arginine in some bacteria and archaea. Here we demonstrate that an uncharacterized AmCP-mediated biosynthetic system functions to biosynthesize the previously uncharacterized and nonproteinogenic amino acid (2S,6R)-diamino-(5R,7)-dihydroxy-heptanoic acid (DADH) in Streptomyces sp. SANK 60404. DADH is incorporated into a novel peptide metabolite, vazabitide A, featuring an azabicyclo-ring structure, by nonribosomal peptide synthetases and successive modification enzymes in this bacterium. As the AmCP-mediated machinery for DADH biosynthesis is widely distributed in bacteria, further analysis of uncharacterized AmCP-containing gene clusters will lead to the discovery of novel bioactive compounds and novel biosynthetic enzymes.
We recently revealed that a Streptomyces strain possesses the gene encoding amino group carrier protein (AmCP). AmCP is involved in the biosynthesis of a previously unidentified nonproteinogenic amino acid, (2S,6R)-diamino-(5R,7)-dihydroxy-heptanoic acid (DADH), which is a core compound for the synthesis of the dipeptide-containing novel natural product vazabitide A. We used polymerase chain reaction (PCR) screening to investigate the diversity of the biosynthetic machinery that uses AmCP; the results revealed that genes encoding AmCP are widely distributed among actinomycetes. The heterologous expression of the AmCP-containing gene cluster from Streptomyces sp. SoC090715LN-17 led to the discovery of s56-p1, a novel natural product. The structure of s56-p1 was determined by spectroscopic analysis; the results revealed that s56-p1 has a putative DADH-derived molecule as the core and also possesses a unique hydrazone unit that is rarely observed in natural products. Our results pave the way for investigations of unexploited AmCP-mediated biosynthesis routes among actinomycetes and of the biosynthetic mechanism of the unique hydrazone unit.
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