Role of Lys5 Residue in β-Strand I of the Sweet-Tasting Protein Brazzein

Abstract

To identify critical residues responsible for sweetness in brazzein and elucidate the interaction mechanisms of brazzein with the sweet taste receptor, three mutants of Lys5 residue in N-terminal β-strand I of brazzein were constructed by site-directed mutagenesis. Mutations of Lys to Asp or Glu at position 5 of brazzein significantly decreased its sweetness, while mutation of Lys5 to Arg resulted in a molecule with slightly decreased sweetness to des-pE1M-brazzein. From these results, it is suggested that the positive charge of Lys5 in β-strand I of brazzein is essential for its function and necessary for structural integrity. Practical Applications Brazzein is a sweet-tasting protein which has been isolated from the fruit of the West African plant Pentadiplandra brazzeana Baillon and is 500 to 2,000 times sweeter than sucrose. Brazzein is attractive as a candidate sweetener for control of obesity, because of its potential sweetness, sugar-like taste and good stability. The present study offers information on the precise interaction mechanism of brazzein with human sweet taste receptor responsible for the sweetness of brazzein, and can be of great value in future design of sweeter brazzein variants.