Mutant d-amino acid oxidase with higher catalytic efficiency toward d-amino acids with bulky side chains
作者:N. V. Komarova、I. V. Golubev、S. V. Khoronenkova、V. I. Tishkov
DOI:10.1007/s11172-012-0193-4
日期:2012.7
d-Amino acid oxidase from the yeast Trigonopsis variabilis (TvDAAO) is widely used in fine organic synthesis, including the preparation of unnatural l-amino acids and α-keto acids. The analysis of the three-dimensional structure of TvDAAO was carried out with the aim of producing the enzyme specific to d-amino acids with bulky side chains. The analysis revealed the residue Phe54 at the entrance to the active site, which controls the substrate access to this site. The residue Phe54 was replaced by residues Ala, Ser, and Tyr. The cultivation of recombinant E. coli strains expressing TvDAAO mutants showed that the mutein with the Phe54Ala substitution had very low stability. Thus, the inactivation of the enzyme occured within 10 min after the cell disruption. The Phe54Ser TvDAAO and Phe54Tyr TvDAAO mutants were obtained as homogeneous preparations, and their thermal stability and catalytic properties were investigated. The introduction of Phe54Ser and Phe54Tyr substitutions resulted in additional stabilization of the protein macromolecule compared to the wild-type TvDAAO. Thus, the half-inactivation time for the mutant enzymes at 54 °C increased by a factor of 1.5 and 2, respectively. As in the case of wild-type TvDAAO, the thermal inactivation of the muteins proceeds via a two-step dissociative mechanism. The introduction of mutations led to a strong change in the substrate specificity profile. The mutants have no activity toward a series of d-amino acids (Phe54Ser TvDAAO toward d-Ala, d-Ser, d-Val, and d-Thr; Phe54Tyr TvDAAO toward d-Ser, d-Tyr, d-Thr, and d-Lys). The catalytic efficiency (the k cat/K M ratio) of the Phe54Ser TvDAAO mutant toward d-amino acids with bulky side chains (d-Lys, d-Asn, d-Phe, d-Tyr, d-Trp, and d-Leu) increased from 2.4 to 7.3 times.
来自变叶酵母(Trigonopsis variabilis)的 d-氨基酸氧化酶(TvDAAO)被广泛用于精细有机合成,包括制备非天然 l-氨基酸和 α-酮酸。对 TvDAAO 的三维结构进行了分析,目的是生产出对具有粗大侧链的 d- 氨基酸具有特异性的酶。分析结果显示,活性位点入口处的残基 Phe54 控制着底物进入该位点。Phe54残基被Ala、Ser和Tyr残基取代。表达 TvDAAO 突变体的重组大肠杆菌菌株的培养结果表明,Phe54Ala 取代后的静音蛋白稳定性非常低。因此,该酶在细胞破坏后 10 分钟内就失活了。研究人员获得了 Phe54Ser TvDAAO 和 Phe54Tyr TvDAAO 突变体的均质制备方法,并对其热稳定性和催化特性进行了研究。与野生型 TvDAAO 相比,Phe54Ser 和 Phe54Tyr 的引入使蛋白质大分子更加稳定。因此,突变体酶在 54 °C 的半失活时间分别增加了 1.5 倍和 2 倍。与野生型 TvDAAO 的情况一样,静音素的热失活也是通过两步解离机制进行的。突变的引入导致底物特异性发生了很大变化。突变体对一系列 d-氨基酸没有活性(Phe54Ser TvDAAO 对 d-Ala、d-Ser、d-Val 和 d-Thr;Phe54Tyr TvDAAO 对 d-Ser、d-Tyr、d-Thr 和 d-Lys)。Phe54Ser TvDAAO 突变体对具有笨重侧链的 d-氨基酸(d-Lys、d-Asn、d-Phe、d-Tyr、d-Trp 和 d-Leu)的催化效率(k cat/K M 比率)从 2.4 倍提高到 7.3 倍。