Recognition and binding of human telomeric G-quadruplex DNA by unfolding protein 1.
The specific recognition by proteins of G-quadruplex structures provides evidence of a functional role for in vivo G-quadruplex structures. As previously reported, the ribonucleoprotein, hnRNP Al, and it is proteolytic derivative, unwinding protein 1 (UP1), bind to and destabilize G-quadruplex structures formed by the human telomeric repeat d(TTAGGG)n. UP1 has been proposed to be involved in the recruitment of telomerase to telomeres for chain extension. In this study, a detailed thermodynamic characterization of the binding of UP1 to a human telomeric repeat sequence, the d[AGGG(TTAGGG)3] G-quadruplex, is presented and reveals key insights into the UP1-induced unfolding of the G-quadruplex structure. The UP1-G-quadruplex interactions are shown to be enthalpically driven, exhibiting large negative enthalpy changes for the formation of both the Na(+) and K(+) G-quadruplex-UP1 complexes (ΔH values of -43 and -19 kcal/mol, respectively). These data reveal three distinct enthalpic contributions from the interactions of UP1 with the Na(+) form of G-quadruplex DNA. The initial interaction is characterized by a binding affinity of 8.5 × 10(8) M(-1) (strand), 200 times stronger than the binding of UP1 to a single-stranded DNA with a comparable but non-quadruplex-forming sequence [4.1 × 10(6) M(-1) (strand)]. Circular dichroism spectroscopy reveals the Na(+) form of the G-quadruplex to be completely unfolded by UP1 at a binding ratio of 2:1 (UP1:G-quadruplex DNA). The data presented here demonstrate that the favorable energetics of the initial binding event are closely coupled with and drive the unfolding of the G-quadruplex structure.
Department of Chemistry, University of Alabama at Birmingham, Birmingham, Alabama 35294, United States.
Jason S
JS
Hudson
Lei
L
Ding
Vu
V
Le
Edwin
E
Lewis
David
D
Graves
D054856:G-Quadruplexes; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D011188:Potassium / Q000737:chemistry; D011485:Protein Binding / Q000502:physiology; D058767:Protein Unfolding; D012964:Sodium / Q000737:chemistry; D016615:Telomere / Q000737:chemistry* / Q000378:metabolism*
D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; C000619656:hnRNPA1 protein, human; D012964:Sodium; D011188:Potassium