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Structure. 2012 Dec 5;20(12):2090-102. doi: 10.1016/j.str.2012.09.013. Epub 2012 Oct 18.

RecA-binding pilE G4 sequence essential for pilin antigenic variation forms monomeric and 5' end-stacked dimeric parallel G-quadruplexes.

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Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY, 10065, USA.


Neisseria gonorrhoeae is an obligate human pathogen that can escape immune surveillance through antigenic variation of surface structures such as pili. A G-quadruplex-forming (G4) sequence (5'-G(3)TG(3)TTG(3)TG(3)) located upstream of the N. gonorrhoeae pilin expression locus (pilE) is necessary for initiation of pilin antigenic variation, a recombination-based, high-frequency, diversity-generation system. We have determined NMR-based structures of the all parallel-stranded monomeric and 5' end-stacked dimeric pilE G-quadruplexes in monovalent cation-containing solutions. We demonstrate that the three-layered all parallel-stranded monomeric pilE G-quadruplex containing single-residue double-chain reversal loops, which can be modeled without steric clashes into the 3 nt DNA-binding site of RecA, binds and promotes E. coli RecA-mediated strand exchange in vitro. We discuss how interactions between RecA and monomeric pilE G-quadruplex could facilitate the specialized recombination reactions leading to pilin diversification.

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