D-Threonine aldolase is an enzyme belonging to the glycine-dependent aldolases, and it catalyzes the reversible aldol reaction of glycine and acetaldehyde to give D-threonine and/or D-allo-threonine. In this study, a putative D-threonine aldolase gene from Delftia sp. RIT313 was cloned and expressed in Escherichia coli BL21 (DE3). The purified enzyme (DrDTA, 47 KDa) exhibited 21.3 U mg⁻¹ activity for the aldol addition of glycine and acetaldehyde in MES-NaOH buffer (pH 6.0) at 50 °C. Both pyridoxal 5′-phosphate and metal ions were needed for the reaction, and the existence of the metal ions enhanced the stability of the enzyme. It was found that the conversion and C_β-stereoselectivity were dramatically influenced by the reaction temperature, co-solvent, amount of enzyme and reaction time, and it is possible to enable the reaction under kinetic control to retain suitable conversion and high stereoselectivity at the β-carbon, thus tackling the “C_β-stereoselectivity problem”. DrDTA showed high activity toward aromatic aldehydes with electron-withdrawing substituents. Under the optimized reaction conditions, phenylserines with a 2′-fluoro- or 3′-nitro-substituent were obtained with >90% conversion and >90% de. In addition, DL-threo-phenylserine and DL-threo-4-(methylsulfonyl)phenylserine were efficiently resolved with an excellent enantiomeric excess value (ee, >99%) using a whole cell biocatalyst in a two-phase system at 1.0 M and 0.3 M, respectively, the highest substrate concentration reported so far. These results suggested that DrDTA might be a promising biocatalyst for producing chiral aromatic β-hydroxy-α-amino acids.

中文翻译：

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一种新型的D-苏氨酸醛缩酶作为一种有前途的生物催化剂，可以高度立体选择性地制备手性芳族β-羟基-α-氨基酸

d -苏氨醛缩酶是属于甘氨酸依赖性醛缩酶的酶，它催化甘氨酸和乙醛，得到的可逆醛醇缩合反应d -苏氨酸和/或d -异体-苏氨酸。在这项研究中，来自Delftia sp。的一个推定的D-苏氨酸醛缩酶基因。RIT313被克隆并在大肠杆菌BL21（DE3）中表达。纯化的酶（DrDTA，47 KDa）表现出21.3 U mg ^-1在50°C的MES-NaOH缓冲液（pH 6.0）中添加甘氨酸和乙醛的醛醇缩合酶的活性。反应需要吡ido醛5'-磷酸和金属离子，并且金属离子的存在增强了酶的稳定性。结果发现，转化和C _β -stereoselectivity受到显着受反应温度，助溶剂，酶和反应时间的量的影响，并且能够以使动力学控制下进行反应，以保持在合适的转化率和高立体选择性β-碳，从而解决了“ _Cβ-立体选择性问题”。DrDTA对具有吸电子取代基的芳族醛显示出高活性。在优化的反应条件下，获得具有2'-氟或3'-硝基取代基的苯基丝氨酸，其转化率> 90％，de> 90％。此外，DL -苏-phenylserine和DL -苏式-4-（甲磺酰基）苯基丝氨酸进行有效地在1.0使用全细胞生物催化剂在两相系统M和优异的对映体过量值（ee，> 99％）分辨迄今为止报道的最高底物浓度分别为0.3M。这些结果表明，DrDTA可能是生产手性芳族β-羟基-α-氨基酸的有前途的生物催化剂。