Structural transitions of a GG-platinated DNA duplex induced by pH, temperature and box A of high-mobility-group protein 1.
[1H, 15N] and 1H NMR, and CD spectroscopy are used to show that the duplex d(A-T-A-C-A-T-Pt 7G-Pt7G-T-A-C-A-T-A).d(T-A-T-G-T-A-C-C-A-T-G-T-A-T), where Pt7G is platinated guanine, containing the cis-[Pt(NH3)2]2+ adduct, undergoes reversible temperature-induced (T0.5 310 K) and pH-induced (pKa approximately 4.8) transitions between kinked-duplex and distorted forms, with the latter forms predominating at high temperature and low pH. A related pH-induced structural change was observed for the unplatinated duplex (pKa 4.69, Hill coefficient n = 1.4) but was less cooperative than for the platinated duplex (n = 2). The pH-induced transition is attributed to protonation of cytosine residues and has wider implications, since many reported NMR studies of DNA are carried out near pH 5 to minimize NH-exchange rates. The [Pt(en)]2+ (where en is 1,2-ethanediamine) GG chelate of the same duplex is shown to exist in kinked and distorted forms, and the [1H,15N]-NMR shifts for the kinked form are indicative of the presence of highly stereospecific interactions with the Pt-NH protons. On binding of the duplex platinated with [Pt(NH3)2]2+ to high-mobility-group protein 1 (HMG1) box A, similar changes in shifts of the Pt-NH3 resonances to those induced by raising the temperature or lowering the pH were observed. The specific changes in 1H-NMR chemical shifts of HMG1 box A are consistent with binding of the platinated duplex (intermediate exchange rate on the 1H-NMR time-scale) to the concave face of the protein via helices I and II and the intervening loop.
Berners-Price
S J
SJ
Faculty of Science and Technology, Griffith University, Nathan, Brisbane, Australia.
Corazza
A
A
Guo
Z
Z
Barnham
K J
KJ
Sadler
P J
PJ
Ohyama
Y
Y
Leng
M
M
Locker
D
D
D001482:Base Composition; D002942:Circular Dichroism; D002945:Cisplatin / Q000737:chemistry*; D006147:Guanine; D006609:High Mobility Group Proteins / Q000737:chemistry / Q000494:pharmacology*; D006859:Hydrogen; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D009587:Nitrogen Isotopes; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry* / Q000187:drug effects; D011485:Protein Binding / Q000235:genetics; D013696:Temperature
D006609:High Mobility Group Proteins; D009587:Nitrogen Isotopes; D009692:Nucleic Acid Heteroduplexes; D006147:Guanine; D006859:Hydrogen; D002945:Cisplatin