The duality of LysU, a catalyst for both Ap4A and Ap3A formation
The duality of LysU, a catalyst for both Ap4A and Ap3A formation
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LysU 的双重性，Ap4A 和 Ap3A 形成的催化剂
DOI：
10.1111/j.1742-4658.2006.05361.x
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
Andrew D. Miller
中科院分区：
文献类型：
--
作者：
M. Wright;Nonlawat Boonyalai;J. Tanner;Alison D. Hindley;Andrew D. Miller
Heat shock inducible lysyl‐tRNA synthetase of Escherichia coli (LysU) is known to be a highly efficient diadenosine 5′,5′′′‐P1,P4‐tetraphosphate (Ap4A) synthase. However, we use an ion‐exchange HPLC technique to demonstrate that active LysU mixtures actually have a dual catalytic activity, initially producing Ap4A from ATP, before converting that tetraphosphate to a triphosphate. LysU appears to be an effective diadenosine 5′,5′′′‐P1,P3‐triphosphate (Ap3A) synthase. Mechanistic investigations reveal that Ap3A formation requires: (a) that the second step of Ap4A formation is slightly reversible, thereby leading to a modest reappearance of adenylate intermediate; and (b) that phosphate is present to trap the intermediate (either as inorganic phosphate, as added ADP, or as ADP generated in situ from inorganic phosphate). Ap3A forms readily from Ap4A in the presence of such phosphate‐based adenylate traps (via a ‘reverse‐trap’ mechanism). LysU is also clearly demonstrated to exist in a phosphorylated state that is more physically robust as a catalyst of Ap4A formation than the nonphosphorylated state. However, phosphorylated LysU shows only marginally improved catalytic efficiency. We note that Ap3A effects have barely been studied in prokaryotic organisms. By contrast, there is a body of literature that describes Ap3A and Ap4A having substantially different functions in eukaryotic cells. Our data suggest that Ap3A and Ap4A biosynthesis could be linked together through a single prokaryotic dual ‘synthase’ enzyme. Therefore, in our view there is a need for new research into the effects and impact of Ap3A alone and the intracellular [Ap3A]/[Ap4A] ratio on prokaryotic organisms.
影响因子：
2.9
作者：
GORBUNOFF, MJ
通讯作者：
GORBUNOFF, MJ
影响因子：
2.9
作者：
GILL, SC;VONHIPPEL, PH
通讯作者：
VONHIPPEL, PH