Importance of Glu53 in the C-terminal region of brazzein, a sweet-tasting protein

BACKGROUND: The sweetness of brazzein, one of the known sweet proteins, is dependent on charges and/or structures of its specific amino acid side chains. As the residues in the C-terminus of brazzein are known to play a critical role in sweetness, the currently unknown function of Glu53 requires further study. RESULTS: To identify important residues responsible for the sweetness of the protein brazzein, four mutants of theGlu53 residue in the C-terminal region of des-pE1M-brazzein, which lacks the N-terminal pyroglutamate, were constructed using site-directed mutagenesis. Mutations of Glu53 substitution to Ala or Asp significantly decreased the sweetness. On the other hand, a Lys mutation resulted in a molecule with sweetness similar to that of des-pE1M-brazzein. Mutation of Glu53 to Arg resulted in a molecule significantly sweeter than des-pE1M-brazzein, which agrees with previous findings showing that mutation with positively charged residues results in a sweeter protein. CONCLUSION: Our results suggest that the residue at position 53 is crucial for the sweetness of brazzein, which may be interacting with the sweet-taste receptor. (C) 2015 Society of Chemical Industry