Platination of full length tRNAAla and truncated versions of the acceptor stem and anticodon loop

Abstract

Nuclear DNA is a well characterized target for many low molecular metal-based drugs, with cisplatin and related antineoplastic compounds as typical examples. Much less is known concerning to what extent targeting of RNA may influence the activity spectrum of these types of drugs. In a preliminary communication by us (Papsai et al., Dalton Trans., 2006, 3515) we were able to show that the folded, three-dimensionally well defined structure of tRNA(Ala) readily interacts with cisplatin. In the present study we have further analyzed the binding preferences within the preferentially targeted stem region (sMh(Ala)) by modulation of the sequence around the G-U wobble base-pair and the net charge of the 3' and 5' ends. Our data show that the adduct profile is strongly influenced by the presence of the 5' end phosphate group. Further, the adduct formation reaction can be prevented by replacement of the G-U wobble base-pair with the fully complementary G-C pair. To further investigate the influence from local sequence on the platination process, a model of the anticodon region (acMh(Ala)) was also investigated. In the absence of consecutive guanine-residues in the stem- and anticodon regions, preferential platination was found to take place at the terminal AG-site in the stem region. However, after introduction of a GG-pair in the anticodon loop, platination was observed also here. At 37 degrees C, pH 6.3 and C(Pt) = 0.10 mM the rate of platination was determined to be ca. 1 x 10(-4) s(-1), with the most rapid reaction observed for interaction with the anticodon model carrying two adjacent guanines in the single-stranded loop. Together, these data show that platination of RNA is highly sequence- and structure-dependent.

Covalent and non-covalent binding of metal complexes to RNA

“…Several examples of covalent binding of platinum complexes to RNA have been herein commented [44,45,47,70,[76][77][78][79][80][81][82][83][84][85][86][87]. Even if the existence of platinum-RNA adducts is undeniable, further biochemical and structural studies are needed to better understand the nature of platinum-RNA adducts as well as their impact on RNA structure and on RNA biological functions.…”

“…This preassociation precedes covalent interaction [90,91], and was shown to influence the binding kinetics also in model systems using short single-stranded DNAs [92]. This finding suggests that short RNAs may also represent good targets for cisplatin [77,78], and prompted further studies to better elucidate the basis of platinum-RNA interaction. Interestingly, in vitro studies performed using mono-aquated platinum complexes have shown that RNA platination kinetically competes or is even preferred over DNA platination [80,93].…”

“…Moreover, GG sequences seem to be more readily platinated when they are in singlestranded regions than when they are involved in base-pairing like in the stem region. All of these findings suggest that small sequence variations, [77,78]. The GC-rich acceptor stem is indicated in grey; the GU wobble base-pair is indicated with a box; the UGC/GGC modification in the anticodon loop is indicated with contours.…”

“…In the sections below the most recent advances in the elucidation of platinum-RNA interactions are summarized, mainly focusing on examples subsequent to the above-mentioned review [39]. In particular, the following aspects are covered: (i) RNA platination kinetics [45,70,[77][78][79] (Sections 3.1 and 3.2); (ii) some examples of platinum binding to structured RNAs [80], focusing on latest insights into platinum binding to ribosomal RNA [44,76,81] (Section 3.3); (iii) the effect of platination on RNA interference [82][83][84] (Section 3.4); (iv) the use of Pt-RNA adducts to study RNA structure and dynamics [85] (Section 3.5) and (v) recent methods to detect RNA-platinum adducts in cells [47,86,87] (Section 3.6).…”

“…The GC-rich acceptor stem is indicated in grey; the GU wobble base-pair is indicated with a box; the UGC/GGC modification in the anticodon loop is indicated with contours. solvent accessibility and overall RNA structure may strongly influence platinum binding [78].…”