Determining the Folding and Unfolding Rate Constants of Nucleic Acids by Biosensor. Application to Telomere G-Quadruplex

• Published in: Journal of the American Chemical Society 2004-10, Vol.126 (41), p.13255-13264
• Main Authors: Zhao, Yong, Kan, Zhong-yuan, Zeng, Zhi-xiong, Hao, Yu-hua, Chen, Hua, Tan, Zheng
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biosensing Techniques - methods; Biosensors; Biotechnology; DNA - chemistry; Fundamental and applied biological sciences. Psychology; G-Quadruplexes; Guanine - chemistry; Humans; Kinetics; Mathematical Computing; Methods. Procedures. Technologies; Nucleic Acid Conformation; Nucleic Acid Hybridization; Oligonucleotides - chemistry; Optics and Photonics; Surface Plasmon Resonance - methods; Telomere - chemistry; Various methods and equipments
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja048398c

Nucleic acid molecules may fold into secondary structures, and the formation of such structures is involved in many biological processes and technical applications. The folding and unfolding rate constants define the kinetics of conformation interconversion and the stability of these structures and is important in realizing their functions. We developed a method to determine these kinetic parameters using an optical biosensor based on surface plasmon resonance. The folding and unfolding of a nucleic acid is coupled with a hybridization reaction by immobilization of the target nucleic acid on a sensor chip surface and injection of a complementary probe nucleic acid over the sensor chip surface. By monitoring the time course of duplex formation, both the folding and unfolding rate constants for the target nucleic acid and the association and dissociation rate constants for the target−probe duplex can all be derived from the same measurement. We applied this method to determine the folding and unfolding rate constants of the G-quadruplex of human telomere sequence (TTAGGG)4 and its association and dissociation rate constants with the complementary strand (CCCTAA)4. The results show that both the folding and unfolding occur on the time scale of minutes at physiological concentration of K+. We speculate that this property might be important for telomere elongation. A complete set of the kinetic parameters for both of the structures allows us to study the competition between the formation of the quadruplex and the duplex. Calculations indicate that the formation of both the quadruplex and the duplex is strand concentration-dependent, and the quadruplex can be efficiently formed at low strand concentration. This property may provide the basis for the formation of the quadruplex in vivo in the presence of a complementary strand.