Critical molecular regions for elicitation of the sweetness of the sweet-tasting protein, thaumatin I.
Thaumatin is an intensely sweet-tasting protein. To identify the critical amino acid residue(s) responsible for elicitation of the sweetness of thaumatin, we prepared mutant thaumatin proteins, using Pichia pastoris, in which alanine residues were substituted for lysine or arginine residues, and the sweetness of each mutant protein was evaluated by sensory analysis in humans. Four lysine residues (K49, K67, K106 and K163) and three arginine residues (R76, R79 and R82) played significant roles in thaumatin sweetness. Of these residues, K67 and R82 were particularly important for eliciting the sweetness. We also prepared two further mutant thaumatin I proteins: one in which an arginine residue was substituted for a lysine residue, R82K, and one in which a lysine residue was substituted for an arginine residue, K67R. The threshold value for sweetness was higher for R82K than for thaumatin I, indicating that not only the positive charge but also the structure of the side chain of the arginine residue at position 82 influences the sweetness of thaumatin, whereas only the positive charge of the K67 side chain affects sweetness.
Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Japan.
Keisuke
K
Ohta
Tetsuya
T
Masuda
Nobuyuki
N
Ide
Naofumi
N
Kitabatake
D000409:Alanine / Q000737:chemistry / Q000235:genetics; D019943:Amino Acid Substitution; D024361:Amino Acids, Basic / Q000235:genetics; D001120:Arginine / Q000737:chemistry / Q000235:genetics; D008239:Lysine / Q000737:chemistry / Q000235:genetics; D008958:Models, Molecular; D009154:Mutation; D010843:Pichia / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D011487:Protein Conformation; D013549:Sweetening Agents / Q000737:chemistry* / Q000302:isolation & purification; D013649:Taste
D024361:Amino Acids, Basic; D010940:Plant Proteins; D013549:Sweetening Agents; C003427:thaumatin protein, plant; D001120:Arginine; D008239:Lysine; D000409:Alanine