Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
EMBO J. 2012 Jan 18;31(2):503-14. doi: 10.1038/emboj.2011.412. Epub 2011 Nov 11.
Structurally similar superfamily I (SF1) and II (SF2) helicases translocate on single-stranded DNA (ssDNA) with defined polarity either in the 5'-3' or in the 3'-5' direction. Both 5'-3' and 3'-5' translocating helicases contain the same motor core comprising two RecA-like folds. SF1 helicases of opposite polarity bind ssDNA with the same orientation, and translocate in opposite directions by employing a reverse sequence of the conformational changes within the motor domains. Here, using proteolytic DNA and mutational analysis, we have determined that SF2B helicases bind ssDNA with the same orientation as their 3'-5' counterparts. Further, 5'-3' translocation polarity requires conserved residues in HD1 and the FeS cluster containing domain. Finally, we propose the FeS cluster-containing domain also provides a wedge-like feature that is the point of duplex separation during unwinding.
结构相似的 I 型（SF1）和 II 型（SF2）解旋酶在单链 DNA（ssDNA）上沿特定极性进行移动，方向为 5'-3'或 3'-5'。两种 5'-3'和 3'-5'方向移动的解旋酶都包含相同的由两个 RecA 样折叠组成的运动核心。极性相反的 SF1 解旋酶以相同的取向结合 ssDNA，并通过在运动结构域内的构象变化的反向序列进行相反方向的移动。在这里，我们使用蛋白水解 DNA 和突变分析，确定 SF2B 解旋酶以与它们的 3'-5'对应物相同的取向结合 ssDNA。此外，5'-3'易位极性需要 HD1 中的保守残基和含铁硫簇的结构域。最后，我们提出含铁硫簇的结构域也提供了一个楔形特征，这是在解旋过程中双链分离的关键点。
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