Prakash Aishwarya, Kieken Fabien, Marky Luis A, Borgstahl Gloria E O
The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA.
J Nucleic Acids. 2011;2011:529828. doi: 10.4061/2011/529828. Epub 2011 Jun 16.
Replication protein A (RPA) plays an essential role in DNA replication by binding and unfolding non-canonical single-stranded DNA (ssDNA) structures. Of the six RPA ssDNA binding domains (labeled A-F), RPA-CDE selectively binds a G-quadruplex forming sequence (5'-TAGGGGAAGGGTTGGAGTGGGTT-3' called Gq23). In K(+), Gq23 forms a mixed parallel/antiparallel conformation, and in Na(+) Gq23 has a less stable (T(M) lowered by ∼20°C), antiparallel conformation. Gq23 is intramolecular and 1D NMR confirms a stable G-quadruplex structure in K(+). Full-length RPA and RPA-CDE-core can bind and unfold the Na(+) form of Gq23 very efficiently, but complete unfolding is not observed with the K(+) form. Studies with G-quadruplex ligands, indicate that TMPyP4 has a thermal stabilization effect on Gq23 in K(+), and inhibits complete unfolding by RPA and RPA-CDE-core. Overall these data indicate that G-quadruplexes present a unique problem for RPA to unfold and ligands, such as TMPyP4, could possibly hinder DNA replication by blocking unfolding by RPA.
复制蛋白A（RPA）通过结合并展开非经典单链DNA（ssDNA）结构在DNA复制中发挥重要作用。在六个RPA ssDNA结合结构域（标记为A - F）中，RPA - CDE选择性地结合一个形成G - 四链体的序列（5'-TAGGGGAAGGGTTGGAGTGGGTT-3'，称为Gq23）。在钾离子存在下，Gq23形成混合平行/反平行构象，而在钠离子存在下，Gq23具有较不稳定的（熔解温度降低约20°C）反平行构象。Gq23是分子内的，一维核磁共振证实了在钾离子存在下其具有稳定的G - 四链体结构。全长RPA和RPA - CDE - 核心可以非常有效地结合并展开Gq23的钠离子形式，但对于钾离子形式未观察到完全展开。对G - 四链体配体的研究表明，TMPyP4对钾离子存在下的Gq23具有热稳定作用，并抑制RPA和RPA - CDE - 核心的完全展开。总体而言，这些数据表明G - 四链体给RPA的展开带来了独特的问题，并且像TMPyP4这样的配体可能通过阻止RPA的展开来阻碍DNA复制。
