![]() ![]() ![]() These include G9–U8 correlations in the loop region of the RNA, and G2–G12 correlations in the RNA stem. These data, acquired on a 14-mer hairpin RNA and on the palindromic Dickerson dodecamer DNA utilizing SMT and the parameters described in the figure caption, show many of the cross-peaks expected from a quality NOESY experiment. (7)įigure 2 shows the kind of problems that may arise in such experiments. (5−8) In these experiments, the magnetization at the exchanging site of interest is replenished either by looped excitations and projections, (9,10) as in loop-projected spectroscopy (L-PROSY), (5) or by continuous frequency-selective saturation or inversion approaches, like in Hadamard magnetization transfer (HMT), (6) heteronuclear magnetization transfer, (8) and selective magnetization transfer (SMT). We have recently proposed a number of ways that can transform this exchange-driven drawback into an advantage, by relying on MT experiments that exploit the replenishments in polarization coming from the solvent water pool. 2D NOESY measurements rely on the latter for their operation NOESY efficiency, however, may suffer when applied to labile NH or OH 1H sites, due to losses from chemical exchanges with the aqueous solvent. This information can be delivered by either transfer of magnetizations between sites undergoing chemical dynamics in the millisecond regime, as in chemical exchange saturation transfer (CEST), (2−4) or by spin dynamics between proximate sites, through the nuclear Overhauser enhancement (NOE) effect. (1) MT NMR experiments can also provide site-specific information about biomolecular structures and dynamics. Magnetization transfer (MT) NMR experiments have long been used to screen the interaction of low-molecular-weight ligands with biomacromolecules. All of these phenomena are herein experimentally demonstrated, and solutions to overcome them are proposed. Although these sidebands usually remain invisible in NMR, they may lead to a very efficient saturation of the main resonance when touched by SMT frequencies. SMT’s long 1H saturation times will then be usually implemented while under 15N decoupling based on cyclic schemes leading to decoupling sidebands. A final source of potential artifact arises in applications where the labile 1Hs of interest are bound to 15N-labeled heteronuclei. The origin and ways to avoid these two effects are described. A second, related but in fact different effect, derives from what we describe as NOE “oversaturation”, a phenomenon whereby the use of overtly intense RF fields overwhelms the cross-relaxation signature. One of these pertains to what we refer to as “spill-over” effects, originating from the use of long saturation pulses leading to changes in the signals of proximate peaks. Repeated experience with SMT has shown that a number of artifacts may arise in these experiments, which may confound the information being sought – particularly when seeking small NOEs among closely spaced resonances. ![]() We have recently discussed how saturation magnetization transfer (SMT) experiments could leverage repeated repolarizations arising from exchanges between labile and water protons to enhance connectivities revealed via the nuclear Overhauser effect (NOE). Magnetization transfer experiments are versatile nuclear magnetic resonance (NMR) tools providing site-specific information. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |