Brazzein is the smallest, most stable, member of a family of sweet-tasting proteins. As such Brazzein presents intriguing possibilities for both scientific research and commercial applications. Its unusual thermostability (activity is retained after 2 hours at 90xC) and high potency (500 times sweeter than sucrose on a weight basis) render it a potential candidate for commercial use as a versatile low calorie sweetener. Its other physical properties, wide range of pH stability (from pH 3 to 8) and small size render it an excellent candidate for NMR studies. Complete proton resonance assignments have been obtained from homonuclear 2D NMR data for all 54 residues in the amino acid sequence. The three-dimensional structure of brazzein has been calculated by distance geometry, using constraints derived from 1H-1H NOE crosspeak intensities, 3JHNH? coupling constants, and 3JH?H? coupling constants. The structure contains a helix-turn-helix motif cradled by a three-stranded beta sheet, and has revealed some previously unknown similarities between brazzein and other small cysteine-rich proteins, including scorpion toxins, plant defense proteins, and trypsin inhibitors. The topology of the structure is supported by chemical shift calculations, hydrogen exchange data, and coupling constant information. Studies are now underway to examine possible structural differences between brazzein variants exhibiting different taste properties.
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