13C-detected HN(CA)C and HMCMC experiments using a single methyl-reprotonated sample for unambiguous methyl resonance assignment

Optimized measurement temperature gives access to the solution structure of a 49 kDa homohexameric β-propeller

Ph1500 is a homohexameric, two-domain protein of unknown function from the hyperthermophilic archaeon Pyrococcus horikoshii. The C-terminal hexamerization domain (Ph1500C) is of particular interest, as it lacks sequence homology to proteins of known structure. However, it resisted crystallization for X-ray analysis, and proteins of this size (49 kDa) present a considerable challenge to NMR structure determination in solution. We solved the high-resolution structure of Ph1500C, exploiting the hyperthermophilic nature of the protein to minimize unfavorable relaxation properties by high-temperature measurement. Thus, the side chain assignment (97%) and structure determination became possible at full proton density. To our knowledge, Ph1500C is the largest protein for which this has been achieved. To minimize detrimental fast water exchange of amide protons at increased temperature, we employed a strategy where the temperature was optimized separately for backbone and side chain experiments.

13C-direct detected NMR experiments for the sequential J-based resonance assignment of RNA oligonucleotides

We present here a set of (13)C-direct detected NMR experiments to facilitate the resonance assignment of RNA oligonucleotides. Three experiments have been developed: (1) the (H)CC-TOCSY-experiment utilizing a virtual decoupling scheme to assign the intraresidual ribose (13)C-spins, (2) the (H)CPC-experiment that correlates each phosphorus with the C4' nuclei of adjacent nucleotides via J(C,P) couplings and (3) the (H)CPC-CCH-TOCSY-experiment that correlates the phosphorus nuclei with the respective C1',H1' ribose signals. The experiments were applied to two RNA hairpin structures. The current set of (13)C-direct detected experiments allows direct and unambiguous assignment of the majority of the hetero nuclei and the identification of the individual ribose moieties following their sequential assignment. Thus, (13)C-direct detected NMR methods constitute useful complements to the conventional (1)H-detected approach for the resonance assignment of oligonucleotides that is often hindered by the limited chemical shift dispersion. The developed methods can also be applied to large deuterated RNAs.