Functional expression in Escherichia coli of the tyrosine-inducible tyrosine ammonia-lyase enzyme from yeast Trichosporon cutaneum for production of p-hydroxycinnamic acid
Deamination of aromatic amino acids phenylalanine or tyrosine is accomplished by the phenylalanine/tyrosine ammonia-lyase (PAL/TAL) enzyme. TAL enzyme is of interest since deamination of tyrosine produces p-hydroxycinnamic acid (pHCA), which has potential for a variety of applications. Among nine microorganisms tested for their ability to produce tyrosine-inducible TAL activity, the yeast, Trichosporon cutaneum showed the highest TAL catalytic activity and the lowest PAL/TAL catalytic efficiency ratio (0.8). The enzyme was purified to near homogeneity and its kinetics studied. The native enzyme appears to be a homo-tetramer with a calculated MW of 294 kDa, subunit MW of 73.5 kDa, and a pI of 5.8. When phenylalanine was used as substrate, the Vmax, Kcat and Km were ∼4.0 ± 0.2 μg/min/mg purified enzyme), 588 ± 29 per min and 4.9 ± 0.9 mM, respectively. However, when tyrosine served as the substrate the Vmax and Kcat were 0.59 ± 0.02 μg/min/mg purified enzyme), and 86.7 ± 29 per min, and substrate binding was apparently cooperative (nH ∼ 2.6 ± 0.4), with S0.5 ∼ 0.6 mM. This is the first reported positive cooperativity for a TAL enzyme. Based on the NH2-terminal and partial internal peptide sequences, the cDNA encoding the enzyme was cloned. Sequence analysis of TcTAL showed 56–62% similarity to other fungal PAL/TAL enzymes. High-level expression (∼30% of total soluble protein, based on SDS-PAGE analysis) of the cDNA in Escherichia coli was achieved using the arabinose inducible araB promoter. The recombinant enzyme possessed both PAL and TAL activities, as evident from the presence of both pHCA and CA in the culture medium.