The role of Q motif in superfamily 2 DNA helicases

DNA解旋酶是ATP依赖的马达蛋白，其将双链DNA解旋以形成所有生物体中DNA代谢所需的单链DNA中间体。超家族2（SF2）是六个解旋酶家族中最大的一个。 由ATP水解产生的能量转化为双链核酸的解旋由七个序列基序（I、Ia、II、III、IV、V和VI）协调。 Q基序位于基序I的上游，由含有恒定谷氨酰胺（Q）残基的9个氨基酸序列（GFXXPXPIQ）组成。 虽然越来越多的证据表明Q基序是解旋酶功能所必需的，但与七个保守的解旋酶基序相比，Q基序的作用较少被认识。 我们的生化和遗传分析表明，在FANCJ解旋酶的Q基序是必不可少的解旋酶活性和DNA修复功能在体内通过调节FANCJ蛋白的二聚化，这是一个新的功能的Q基序。 目前还不清楚这种功能是否在FANCJ样解旋酶（ChlR1和RTEL1）和RecQ解旋酶家族中是保守的，这些家族在其一级序列中都含有Q基序。 使用结构，生物化学和细胞方法的组合，我们的研究旨在1）继续确定FANCJ解旋酶中Q基序的作用，2）检查FANCJ样解旋酶ChlR1和RTEL1中Q基序的作用，3）确定RecQ解旋酶家族中Q基序的功能和结构作用。 从本研究中获得的结果将推进SF2 DNA解旋酶的结构元件的基础知识，它在DNA复制，修复，重组，转录，染色体分离和端粒维持中起着重要作用，从古细菌，细菌，真核生物保守。

DNA helicases are ATP-dependent motor proteins that unwind duplex DNA to form single stranded DNA intermediates that are required for DNA metabolism in all organisms. Superfamily 2 (SF2) is the largest of six helicase families. The conversion of energy derived from ATP hydrolysis into unwinding of double-stranded nucleic acids is coordinated by seven sequence motifs (I, Ia, II, III, IV, V, and VI). The Q motif is located upstream of motif I and consists of a nine amino acid sequence (GFXXPXPIQ) containing an invariant glutamine (Q) residue. Although increasing evidences suggest that the Q motif is essential for helicase function, the role of Q motif is less appreciated compared with the seven conserved helicase motifs. Our biochemical and genetic analyses demonstrate that the Q motif in FANCJ helicase is essential for its helicase activity and DNA repair function in vivo by regulation of the dimerization of FANCJ protein, which is a novel function for the Q motif. It remains unknown whether such function is conserved in FANCJ-like helicases (ChlR1 and RTEL1) and the RecQ helicase family, which all contain the Q motif in their primary sequence. Using a combination of structural, biochemical, and cellular approaches, our studies aim to 1) Continue to define the role of the Q motif in the FANCJ helicase, 2) Examine the role of the Q motif in the FANCJ-like helicases ChlR1 and RTEL1, and 3) Determine the functional and structural roles of the Q motif in the RecQ helicase family. The results obtained from this study will advance fundamental knowledge of structural elements of SF2 DNA helicases, which play vital roles in DNA replication, repair, recombination, transcription, chromosome segregation, and telomere maintenance that conserved from archaea, bacteria, to eukaryotes.