Biochemical characterization of a novel tyrosine phenol-lyase from Fusobacterium nucleatum for highly efficient biosynthesis of l-DOPA

Abstract

Tyrosine phenol-lyase (TPL) catalyzes the reversible cleavage of l-tyrosine to phenol, pyruvate and ammonia. When pyrocatechol is substituted for phenol, l-dihydroxyphenylalanine (l-DOPA) is produced. The TPL-catalyzed route was regarded as the most economic process for l-DOPA production. In this study, a novel TPL from Fusobacterium nucleatum (Fn-TPL) was successfully overexpressed in Escherichia coli and screened for l-DOPA synthesis with a specific activity of 2.69Umg^-1. Fn-TPL was found to be a tetramer, and the optimal temperature and pH for α, β-elimination of l-tyrosine was 60°C and pH 8.5, respectively. The enzyme showed broad substrate specificity toward natural and synthetic l-amino acids. Kinetic analysis suggested that the k_cat/K_m value for l-tyrosine decomposition was much higher than that for l-DOPA decomposition, while Fn-TPL exhibited similar catalytic efficiency for synthesis of l-tyrosine and l-DOPA. With whole cells of recombinant E. coli as biocatalyst, l-DOPA yield reached 110gL^-1 with a pyrocatechol conversion of 95%, which was comparable to the reported highest level. The results demonstrated the great potential of Fn-TPL for industrial production of l-DOPA.

Keywords: Fusobacterium nucleatum; Kinetic analysis; L-DOPA; Substrate specificity; Tyrosine phenol-lyase.