Studies on solution NMR structure of brazzein - Secondary structure and molecular scaffold

Brazzein is a sweet-tasting protein isolated from the fruit of West African plant Pentadiplandra brazzeana Baillon. It is the smallest and the most wa ter-soluble sweet protein discovered so far and is highly thermostable. The proton NMR study of brazzein at 600 MHz (pH 3.5, 300 K) is presented. The complete sequence specific assignments of the individual backbone and sidec hain proton resonances were achieved using through-bond and through-space c onnectivities obtained from standard tyro-dimensional NMR techniques. The s econdary structure of brazzein contains one a-helix (residues 21-29), one s hort 3(10)-helix (residues 14-17), two strands of antiparallel P-sheet (res idues 34-39, 44-50) and probably a third strand (residues 5-7) near the N-t erminus. A comparative analysis found that brazzein shares a so-called ' cy steine-stabilized alpha-beta' (CS alpha beta) motif with scorpion neurotoxi ns, insect defensins and plant gamma-thionins. The significance of this mul ti-function motif, the possible active sites and the structural basis of th ermostability were discussed.