School of Life Science, Shanxi University, Taiyuan, 030006, China.
Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan, 030006, China.
J Eukaryot Microbiol. 2021 Mar;68(2):e12834. doi: 10.1111/jeu.12834. Epub 2021 Feb 17.
Cysteine is implicated in important biological processes. It is synthesized through two different pathways. Cystathionine β-synthase and cystathionine γ-lyase participate in the reverse transsulfuration pathway, while serine acetyltransferase and cysteine synthase function in the de novo pathway. Two evolutionarily related pyridoxal 5'-phosphate-dependent enzymes, cystathionine β-synthase TtCBS1 (TTHERM_00558300) and cysteine synthase TtCSA1 (TTHERM_00239430), were identified from a freshwater protozoan Tetrahymena thermophila. TtCbs1 contained the N-terminal heme binding domain, catalytic domain, and C-terminal regulatory domain, whereas TtCsa1 consisted of two α/β domains. The catalytic core of the two enzymes is similar. TtCBS1 and TtCSA1 showed high expression levels in the vegetative growth stage and decreased during the sexual developmental stage. TtCbs1 and TtCsa1 were localized in the cytoplasm throughout different developmental stages. His-TtCbs1 and His-TtCsa1 were expressed and purified in vitro. TtCbs1 catalyzed the canonical reaction with the highest velocity and possessed serine sulfhydrylase activity. TtCsa1 showed cysteine synthase activity with high K for O-acetylserine and low K for sulfide and also had serine sulfhydrylase activity toward serine. Both TtCbs1 and TtCsa1 catalyzed hydrogen sulfide producing. TtCBS1 knockdown and TtCSA1 knockout mutants affected cysteine and glutathione synthesis. TtCbs1 and TtCsa1 are involved in cysteine synthesis through two different pathways in T. thermophila.
半胱氨酸参与重要的生物过程。它通过两条不同的途径合成。胱硫醚β-合酶和胱硫醚γ-裂合酶参与反硫代途径，而丝氨酸乙酰转移酶和半胱氨酸合酶则在从头途径中发挥作用。两种进化上相关的吡哆醛 5'-磷酸依赖酶，胱硫醚β-合酶 TtCBS1（TTHERM_00558300）和半胱氨酸合酶 TtCSA1（TTHERM_00239430），从淡水原生动物嗜热四膜虫中鉴定出来。TtCbs1 含有 N 端血红素结合结构域、催化结构域和 C 端调节结构域，而 TtCsa1 由两个α/β结构域组成。两种酶的催化核心相似。TtCBS1 和 TtCSA1 在营养生长阶段表达水平较高，在有性发育阶段下降。TtCbs1 和 TtCsa1 在不同的发育阶段都定位于细胞质中。His-TtCbs1 和 His-TtCsa1 在体外表达和纯化。TtCbs1 以最高速度催化典型反应，并具有丝氨酸巯基酶活性。TtCsa1 表现出半胱氨酸合酶活性，对 O-乙酰丝氨酸的 K 值较高，对硫化物的 K 值较低，对丝氨酸也具有丝氨酸巯基酶活性。TtCbs1 和 TtCsa1 都能催化硫化氢的产生。TtCBS1 敲低和 TtCSA1 敲除突变体影响半胱氨酸和谷胱甘肽的合成。TtCbs1 和 TtCsa1 在嗜热四膜虫中通过两条不同的途径参与半胱氨酸合成。
