Institute of Technology, University of Tartu, 50411 Tartu, Estonia.
Department of Molecular Biology, Umeå University, SE-901 87 Umea, Sweden.
Proc Natl Acad Sci U S A. 2017 Apr 4;114(14):3726-3731. doi: 10.1073/pnas.1617868114. Epub 2017 Mar 20.
The alarmone nucleotides guanosine pentaphosphate (pppGpp) and tetraphosphate (ppGpp), collectively referred to as (p)ppGpp, are key regulators of bacterial growth, stress adaptation, pathogenicity, and antibiotic tolerance. We show that the tetrameric small alarmone synthetase (SAS) RelQ from the Gram-positive pathogen is a sequence-specific RNA-binding protein. RelQ's enzymatic and RNA binding activities are subject to intricate allosteric regulation. (p)ppGpp synthesis is potently inhibited by the binding of single-stranded RNA. Conversely, RelQ's enzymatic activity destabilizes the RelQ:RNA complex. pppGpp, an allosteric activator of the enzyme, counteracts the effect of RNA. Tetramerization of RelQ is essential for this regulatory mechanism, because both RNA binding and enzymatic activity are abolished by deletion of the SAS-specific C-terminal helix 5α. The interplay of pppGpp binding, (p)ppGpp synthesis, and RNA binding unites two archetypal regulatory paradigms within a single protein. The mechanism is likely a prevalent but previously unappreciated regulatory switch used by the widely distributed bacterial SAS enzymes.
警报核苷酸鸟苷五磷酸（pppGpp）和四磷酸（ppGpp），统称为（p）ppGpp，是细菌生长、应激适应、致病性和抗生素耐受性的关键调节剂。我们表明，革兰氏阳性病原体 的四聚体小警报核苷酸合成酶（SAS）RelQ 是一种序列特异性 RNA 结合蛋白。RelQ 的酶活性和 RNA 结合活性受到复杂的变构调节。单链 RNA 的结合强烈抑制（p）ppGpp 的合成。相反，RelQ 的酶活性会使 RelQ:RNA 复合物不稳定。pppGpp 是酶的变构激活剂，可抵消 RNA 的作用。RelQ 的四聚化对于这种调节机制至关重要，因为删除 SAS 特异性 C 末端螺旋 5α 会使 RNA 结合和酶活性都丧失。pppGpp 结合、（p）ppGpp 合成和 RNA 结合的相互作用将两个典型的调节范例结合在单个蛋白内。该机制可能是广泛分布的细菌 SAS 酶中普遍存在但以前未被重视的调节开关。
