Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo, Japan.
Mol Cell. 2010 Aug 13;39(3):410-20. doi: 10.1016/j.molcel.2010.07.018.
The 21(st) amino acid, selenocysteine (Sec), is assigned to the codon UGA and is biosynthesized on the selenocysteine-specific tRNA (tRNA(Sec)) with the corresponding anticodon. In archaea/eukarya, tRNA(Sec) is ligated with serine by seryl-tRNA synthetase (SerRS), the seryl moiety is phosphorylated by O-phosphoseryl-tRNA kinase (PSTK), and the phosphate group is replaced with selenol by Sep-tRNA:Sec-tRNA synthase. PSTK selectively phosphorylates seryl-tRNA(Sec), while SerRS serylates both tRNA(Ser) and tRNA(Sec). In this study, we determined the crystal structures of the archaeal tRNA(Sec).PSTK complex. PSTK consists of two independent linker-connected domains, the N-terminal catalytic domain (NTD) and the C-terminal domain (CTD). The D-arm.CTD binding occurs independently of and much more strongly than the acceptor-arm.NTD binding. PSTK thereby distinguishes the characteristic D arm with the maximal stem and the minimal loop of tRNA(Sec) from the canonical D arm of tRNA(Ser), without interacting with the anticodon. This mechanism is essential for the UGA-specific encoding of selenocysteine.
第 21 个氨基酸，硒代半胱氨酸（Sec），被分配给 UGA 密码子，并在具有相应反密码子的硒代半胱氨酸特异性 tRNA（tRNA（Sec））上生物合成。在古菌/真核生物中，tRNA（Sec）由丝氨酰-tRNA 合成酶（SerRS）与丝氨酸连接，丝氨酸部分被 O-磷酸丝氨酸-tRNA 激酶（PSTK）磷酸化，磷酸基团被硒代转移酶替换为硒代半胱氨酸。PSTK 选择性地磷酸化 seryl-tRNA（Sec），而 SerRS 则使 tRNA（Ser）和 tRNA（Sec）都丝氨酸化。在这项研究中，我们确定了古菌 tRNA（Sec）.PSTK 复合物的晶体结构。PSTK 由两个独立的连接域组成，即 N 端催化结构域（NTD）和 C 端结构域（CTD）。D 臂.CTD 结合独立于并比受体臂.NTD 结合强得多。因此，PSTK 从 tRNA（Ser）的典型 D 臂区分出具有最大茎和最小环的特征性 D 臂，而不与反密码子相互作用。这种机制对于 UGA 特异性编码硒代半胱氨酸是必不可少的。
