Donmez Ilker, Patel Smita S
Department of Biochemistry, UMDNJ, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA.
Nucleic Acids Res. 2006;34(15):4216-24. doi: 10.1093/nar/gkl508. Epub 2006 Aug 25.
Bacteriophage T7 helicase (T7 gene 4 helicase-primase) is a prototypical member of the ring-shaped family of helicases, whose structure and biochemical mechanisms have been studied in detail. T7 helicase assembles into a homohexameric ring that binds single-stranded DNA in its central channel. Using RecA-type nucleotide binding and sensing motifs, T7 helicase binds and hydrolyzes several NTPs, among which dTTP supports optimal protein assembly, DNA binding and unwinding activities. During translocation along single stranded DNA, the subunits of the ring go through dTTP hydrolysis cycles one at a time, and this probably occurs also during DNA unwinding. Interestingly, the unwinding speed of T7 helicase is an order of magnitude slower than its translocation rate along single stranded DNA. The slow unwinding rate is greatly stimulated when DNA synthesis by T7 DNA polymerase is coupled to DNA unwinding. Using the T7 helicase as an example, we highlight critical findings and discuss possible mechanisms of helicase action.
噬菌体T7解旋酶（T7基因4解旋酶-引物酶）是环状解旋酶家族的典型成员，其结构和生化机制已得到详细研究。T7解旋酶组装成一个同源六聚体环，该环在其中心通道中结合单链DNA。利用RecA型核苷酸结合和传感基序，T7解旋酶结合并水解几种NTP，其中dTTP支持最佳的蛋白质组装、DNA结合和解旋活性。在沿着单链DNA转运过程中，环的亚基一次经历一个dTTP水解循环，这可能在DNA解旋过程中也会发生。有趣的是，T7解旋酶的解旋速度比其沿着单链DNA的转运速率慢一个数量级。当T7 DNA聚合酶的DNA合成与DNA解旋偶联时，缓慢的解旋速率会受到极大刺激。以T7解旋酶为例，我们重点介绍关键发现并讨论解旋酶作用的可能机制。
