Wyniki wyszukiwania - BazTech

Ograniczanie wyników

Powiadomienia systemowe

Sesja wygasła!

Znaleziono wyników: 1

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: 13C/15N isotopic labeling

Sortuj według:

Ogranicz wyniki do:

Spektroskopia NMR w badaniach strukturalnych kwasów nukleinowych. Część 1.

Gdaniec Z.

Wiadomości Chemiczne

2005

[Z] 59, 1-2

47--65

NMR spectroscopy is a powerful method that allows detetmination of the structure and dynamics of nucleic acids and their complexes in solution with atomic resolution. A major breakthrough in the structure determination of nucleic acids by NMR was introduction of advanced and efficient methods for the labeling of RNA and DNA with13C and 15N and development of multidimensional, heteronuclear NMR techniques analogous to those used in protein NMR spectroscopy. The resonance assignment is a crucial step in the NMR study. A spectrum must be assigned before useful structural information can be extracted. The assignment of RNA is considerably more difficult than for DNA of similar size. This is mainly due to the much narrower spectral dispersion of the H2', H3', H4' and H'/5 " ribose protons relative to DNA. The methodology for sequential assignment of nucleic acids via lomonuclear NMR techniques relies on the assumption of helical structure and therefore fails in the case of nonhelical structures, that is typical of RNA. Development of 13C/15N labeling techniques has afforded heteronuclear multidementional experiments that utilize the favorable properties of 13C and 15N nuclei such as large one-and two-bond heteronuclear scalar coupling constants and large chemical shift dispersion. These experiments provide increased sensitivity of double and triple resonance experiments and help in overcoming the problem of severe spectral overlap. Progress in novel NMR methods stimulated also a design of experiments for conformationindependent sequential assignment. In nucleic acids, experiments that correlate base resonances among themselves as well as with sugar resonances allow unambiguous spectral assignment for the structures, where the conventional NOE-based methods may not be applied. Assignments of highly overlapped sugar resonances are facilitated enormously by the application of correlated experiments based on 13C-13C transfer. Additionally, triple resonance experiments allow correlation of neighboring nucleotides through the phosphodiester backbone. The arsenal of existing methods in structure calculations of nuclcic acids by NMR spectroscopy has recently been extended. For example, NMR methods have been developed to detect and measure scalar couplings via hydrogen bonds. The information about hydrogen bonds provides very useful restraints for structural determination, especially in case of noncanonical motifs. Furthermore, the use of methods that introduce anisotropic environments for nucleic acids in solution allows the measurement of residual dipolar couplings (RDC). RDCs yield orientation, rather than distance-based constraints. The RDCs contain global structural information on nucleic acids that cannot be obtained by standard solution NMR techniques. These constraints can both improve the local structure of nucleic acids and provide novel data on the global structure. Another NMR technique, TROSY has been introduced to effectively suppress transverse relaxation of 1H-15N and 1H-13C moieties. TROSY selects exclusively the narrow line of a 1H-15N doublet or 1H-13C multiplet, yielding improved spectral resolution and increased sensitivity of NMR experiment. Recent advances in solution NMR techniques provide tools for structural studies of large (> 30 residues) nucleic acids molecules.