title: Stabilization of a G-Quadruplex from Unfolding by Replication Protein A Using Potassium and the Porphyrin TMPyP4.
abstract: 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.
authors.affiliation: The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA.
authors.forename: Aishwarya
authors.initials: A
authors.lastname: Prakash
authors.forename: Fabien
authors.initials: F
authors.lastname: Kieken
authors.forename: Luis A
authors.initials: LA
authors.lastname: Marky
authors.forename: Gloria E O
authors.initials: GE
authors.lastname: Borgstahl