Helicase unwinding: active or merely perfect?
Helicase unwinding: active or merely perfect?
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解旋酶解旋：主动还是仅仅完美？
DOI：
10.1016/j.jmb.2012.04.030
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发表时间：
2012
影响因子：
5.6
通讯作者：
Webb,MartinR
中科院分区：
文献类型：
--
作者：
Bianco,PieroR;Webb,MartinR
DNA解旋酶最初是作为利用ATP水解的能量将双链DNA（dsDNA）解旋成两条单链的酶而分离的。1所有的DNA解旋酶都有几个共同的生化特性。这些包括与单链DNA（ssDNA）和dsDNA的结合以及核苷5′-三磷酸（通常为ATP）水解，再加上双链体DNA的极性解旋成其组成单链。虽然DNA解旋酶作用的结果是相同的（即dsDNA解旋），但它们实现这一目标的方式是相当不同的。这取决于酶的体内作用、其寡聚体结构以及与其相互作用的伴侣蛋白。4，5已经提出了几种方法来对RNA和DNA的解旋酶的多样性进行分类，包括基于结构和序列的分组6或考虑物理性质，如运动方向。7此外，由于许多解旋酶沿着ssDNA移位并将双链体解旋成其组成链，因此用于分离链的机制也可用于对这些酶进行分类。8这种分组将解旋酶分为被动和主动DNA解旋纳米机器。被动酶是一种机会酶，它与单链尾部结合，然后等待相邻的双链体打开，主要是通过热波动。[9]一旦双链体打开，解旋酶就会捕获剥离的末端，因为它现在会在ATP水解的驱动下沿着新生的ssDNA链移动一个或几个碱基。然后，它必须等待随后的碱基对打开事件，然后才能发生进一步的移动。预期使用这种机制的酶将在ssDNA上快速移位，但通过dsDNA移动得慢得多，此外，其解旋将通过增加双链体的GC含量来抑制。此外，ATP水解不会直接与解旋偶联，而是在ATP水解循环期间通过一系列构象变化来驱动ssDNA向前易位。最后，被动酶的DNA解旋将通过使DNA双链体不稳定的辅助力来增强：机械分离DNA链需要约15 pN的力。10
DNA helicases were first isolated as enzymes that utilize the energy of ATP hydrolysis to unwind double-stranded DNA (dsDNA) into two single strands. 1 All DNA helicases share several common biochemical properties. These include binding to single-stranded DNA (ssDNA) and dsDNA and nucleoside 5′-triphosphate (generally ATP) hydrolysis, coupled to polar unwinding of duplex DNA into its component single strands. 2, 3 Although the outcome of the action of DNA helicases is the same (ie, dsDNA unwinding), the manner in which they achieve this goal is quite diverse. This is dictated by the in vivo role of the enzyme, its oligomeric structure, and the partner proteins with which it interacts. 4, 5 Several methods have been proposed to classify this diversity of helicases, both for RNA and DNA, including groupings based on structure and sequence6 or also taking into account physical properties, such as directionality of movement. 7Furthermore, as many helicases translocate along ssDNA and unwind the duplex into its component strands, the mechanism used to separate strands can also be used to classify these enzymes. 8 This grouping classifies helicases into passive and active DNA unwinding nanomachines. A passive enzyme is an opportunistic one that binds to a single-strand tail and then waits for the adjacent duplex to open, primarily by thermal fluctuations. 9 Once the duplex opens, the helicase captures the flayed end, as it now moves one or a few bases along the nascent ssDNA strand, driven by ATP hydrolysis. Then, it has to wait for a subsequent base-pair opening event before further movement can occur. An enzyme using this mechanism would be expected to translocate rapidly on ssDNA but move much more slowly through dsDNA, and furthermore, its unwinding would be inhibited by increasing GC content of the duplex. In addition, ATP hydrolysis would not be directly coupled to unwinding but instead would be used to drive ssDNA translocation forward through a series of conformation changes during the ATP hydrolysis cycle. Finally, DNA unwinding by passive enzymes would be enhanced by an assisting force that destabilizes the DNA duplex:~ 15 pN of force is required to separate the strands of DNA mechanically. 10