Selective recognition of a DNA G-quadruplex by an engineered antibody.

Particular guanine rich nucleic acid sequences can fold into stable secondary structures called G-quadruplexes. These structures have been identified in various regions of the genome that include the telomeres, gene promoters and UTR regions, raising the possibility that they may be associated with biological function(s). Computational analysis has predicted that intramolecular G-quadruplex forming sequences are prevalent in the human genome, thus raising the desire to differentially recognize genomic G-quadruplexes. We have employed antibody phage display and competitive selection techniques to generate a single-chain antibody that shows >1000-fold discrimination between G-quadruplex and duplex DNA, and furthermore >100-fold discrimination between two related intramolecular parallel DNA G-quadruplexes. The amino acid sequence composition at the antigen binding site shows conservation within the light and heavy chains of the selected scFvs, suggesting sequence requirements for G-quadruplex recognition. Circular dichroism (CD) spectroscopic data showed that the scFv binds to the prefolded G-quadruplex and does not induce G-quadruplex structure formation. This study demonstrates the strongest discrimination that we are aware of between two intramolecular genomic G-quadruplexes.