Biochemical characterization of thermostable ω-transaminase from Sphaerobacter thermophilus and its application for producing aromatic β- and γ-amino acids

• A (S)-selective thermostable ω-transaminase from eubacterium Sphaerobacter thermophilus was functionally characterized.
• The enzyme showed activity towards a broad range of substrates including amines, β- and γ-amino acids.
• Optically pure β- and γ-amino acids were produced using this enzyme via kinetic resolution and asymmetric synthesis.

An (S)-ω-transaminase from the thermophilic eubacterium Sphaerobacter thermophilus was expressed and functionally characterized. The enzyme showed good stability at high temperature and in the presence of various substrates. Substrate specificity analysis showed that the enzyme had activity towards a broad range of substrates including amines, β- and γ-amino acids. The purified enzyme showed a specific activity of 3.3 U/mg towards rac-β-phenylalanine at 37 °C. The applicability of this enzyme as an attractive biocatalyst was demonstrated by synthesizing optically pure β- and γ-amino acids. Among the various beta and gamma amino acids produced via asymmetric synthesis, (S)-4-amino-4-(4-methoxyphenyl)-butanoic acid showed highest analytical yield (82%) with excellent enantiomeric excess (>99%).