Engineering of a bacterial tyrosinase for improved catalytic efficiency towards D-tyrosine using random and site directed mutagenesis approaches
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Martin, Leona B.
O'Connor, Kevin E.
Article (Published version)
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The tyrosinase gene from Ralstonia solanacearum (GenBank NP518458) was subjected to random mutagenesis resulting in tyrosinase variants (RVC10 and RV145) with up to 3.2-fold improvement in kcat, 5.2-fold lower Km and 16-fold improvement in catalytic efficiency for D-tyrosine. Based on RVC10 and RV145 mutated sequences, single mutation variants were generated with all variants showing increased kcat for D-tyrosine compared to the wild type (WT). All single mutation variants based on RV145 had a higher kcat and Km value compared to the RV145 and thus the combination of four mutations in RV145 was antagonistic for turnover, but synergistic for affinity of the enzyme for D-tyrosine. Single mutation variant 145_V153A exhibited the highest (6.9-fold) improvement in kcat and a 2.4-fold increase in Km compared to the WT. Two single mutation variants, C10_N322S and C10_T183I reduced the Km up to 2.6-fold for D-tyrosine but one variant 145_V153A increased the Km 2.4-fold compared to the WT. Homo...logy based modeling of R. solanacearum tyrosinase showed that mutation V153A disrupts the van der Waals interactions with an -helix providing one of the conserved histidine residues of the active site. The kcat and Km values for L-tyrosine decreased for RV145 and RVC10 compared to the WT. RV145 exhibited a 2.1-fold high catalytic efficiency compared to the WT which is a 7.6-fold lower improvement compared to D-tyrosine. RV145 exhibited a threefold higher monophenolase:diphenolase activity ratio for D-tyrosine:D-DOPA and a 1.4-fold higher L-tyrosine:L-DOPA activity ratio compared to the WT. Biotechnol. Bioeng. 2013; 110: 1849-1857.
Keywords:tyrosinase / D-tyrosine / random mutagenesis / site specific mutagenesis / enzyme catalysis / homology modeling
Source:Biotechnology and Bioengineering, 2013, 110, 7, 1849-1857
- Wiley-Blackwell, Hoboken