Combining 2H and 13C Selective Enrichment to Probe Protein Dynamics
The dipolar interactions between 13C nuclei and the directly attached 1H nuclei offer a potentially rich set of spectroscopic monitors of the dynamical behavior of biological macromolecules. However, in contrast to the more widely exploited 1H-15N dipoles of the mainchain amide resonances of proteins, additional technical complexities have impeded the more extensive use of 13C relaxation analysis. As for the case of 15N studies, the low sensitivity of natural abundance samples have limited 13C relaxation studies to quite small highly soluble systems. On the other hand uniform enrichment introduces scalar and dipolar interactions between directly bonded 13C nuclei which confound the interpretation of the conventional pulse sequences used in relaxation analysis. Progress has been reported in the development of pulse sequences to circumvent some of the complications arising from geminal 13C nuclei,1,2 but a general solution is not yet available. An alternate approach which allows for extensive high levels of site specific enrichment with minimal occurrence of geminal 13C-13C couplings can be achieved via protein expression in bacterial strains carrying suitable metabolic lesions so as to direct the flow of isotopic label from selectively enriched carbon sources.
KeywordsIsotope Shift Quadrupolar Interaction Scalar Coupling Methylene Position Stereochemical Assignment
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