ABSTRACT
Synthetic metabolic pathways have been constructed for the production of enantiopure (
R
)- and (
S
)-3-hydroxybutyrate (3HB) from glucose in recombinant
Escherichia coli
strains. To promote maximal activity, we profiled three thiolase homologs (BktB, Thl, and PhaA) and two coenzyme A (CoA) removal mechanisms (Ptb-Buk and TesB). Two enantioselective 3HB-CoA dehydrogenases, PhaB, producing the (
R
)-enantiomer, and Hbd, producing the (
S
)-enantiomer, were utilized to control the 3HB chirality across two
E. coli
backgrounds, BL21Star(DE3) and MG1655(DE3), representing
E. coli
B- and K-12-derived strains, respectively. MG1655(DE3) was found to be superior for the production of each 3HB stereoisomer, although the recombinant enzymes exhibited lower in vitro specific activities than BL21Star(DE3). Hbd in vitro activity was significantly higher than PhaB activity in both strains. The engineered strains achieved titers of enantiopure (
R
)-3HB and (
S
)-3HB as high as 2.92 g liter
−1
and 2.08 g liter
−1
, respectively, in shake flask cultures within 2 days. The NADPH/NADP
+
ratio was found to be two- to three-fold higher than the NADH/NAD
+
ratio under the culture conditions examined, presumably affecting in vivo activities of PhaB and Hbd and resulting in greater production of (
R
)-3HB than (
S
)-3HB. To the best of our knowledge, this study reports the highest (
S
)-3HB titer achieved in shake flask
E. coli
cultures to date.
摘要
已经构建了生产对映体纯(
R
)和(
S
)-3-羟基丁酸(3HB)的合成代谢途径。
大肠杆菌
菌株。为了提高最大活性,我们研究了三种硫醇酶同源物(BktB、Thl 和 PhaA)和两种辅酶 A(CoA)去除机制(Ptb-Buk 和 TesB)。两种对映体选择性 3HB-CoA 脱氢酶(PhaB)产生(
R
)对映体的 PhaB 和产生(
S
)-对映体的 Hbd 被用来控制两种大肠杆菌中 3HB 的手性。
大肠杆菌
BL21Star(DE3) 和 MG1655(DE3)背景中控制 3HB 手性,这两种背景代表了
大肠杆菌
B和 K-12 衍生菌株。尽管重组酶的体外特异性活性低于 BL21Star(DE3),但发现 MG1655(DE3) 在生产每种 3HB 立体异构体方面都更胜一筹。两种菌株的 Hbd 体外活性都明显高于 PhaB 活性。工程菌株获得的对映体纯度 (
R
)-3HB和(
S
)-3HB的滴度高达 2.92 克升-1
-1
和 2.08 克升
-1
在 2 天内,摇瓶培养物中的 NADPH/NADP 浓度分别高达 2.92 克升-1 和 2.08 克升-1。NADPH/NADP
+
比率比 NADH/NAD
+
比率高出两到三倍,这可能会影响 PhaB 和 Hbd 的体内活性,导致产生更多的 (
R
)-3HB的产量大于(
S
)-3HB。据我们所知,本研究报告了最高的 (
S
)-3HB滴度最高的摇瓶
大肠杆菌
培养物中达到的最高 ( S )-3HB 滴度。