Selenium, a vital element in the human body, is a cardinal contributor to cellular antioxdative defense and cancer prevention. Selenoproteins, which contain the reactive amino acid selenocysteine, participate in redox and electron transfer reactions. The 25 human selenoproteins are powerful enzymes that utilize the selenocysteine in conjunction with a nearby cysteine in their active site. These so called redox motifs govern the protein redox potential and hence chemical reactivity. We measured the differences in the inherent flexibility of selenocysteine in different redox motifs: the cysteine-selenocysteine redox motif is present in thioredoxin reductase while the cysteine-X-X-selenocysteine redox motif (X stands for any amino acid) is found in cell signaling selenoproteins. 77selenocysteine was incorporated into proteins by manipulating E. coli selenium incorporation machinery. We have measured the relaxation properties of the selenium in the redox motif using solution-state selenium NMR. Our NMR data show that the selenocysteine in the oxidized cysteine-selenocysteine redox motif is much more rigid than that of the cysteine-X-X-selenocysteine redox motif. In contrast, the flexibility of the active site selenocysteine is greater in the reduced cysteine-selenocysteine than in the reduced cysteine-X-X-selenocysteine redox motif.

77Se NMR spectroscopy of selenoproteins' redox motifs

244th National Meeting (2012)

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