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Chemical Senses Advance Access published online on September 14, 2005
Chemical Senses, doi:10.1093/chemse/bji060
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© The Author 2005. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oupjournals.org
Accepted August 12, 2005

Article

Structure-Sweetness Relationship in Egg White Lysozyme: Role of Lysine and Arginine Residues on the Elicitation of Lysozyme Sweetness

Tetsuya Masuda 1, Nobuyuki Ide 1, and Naofumi Kitabatake 1*

1 Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Uji, Kyoto 611-0011, Japan

* To whom correspondence should be addressed.
Naofumi Kitabatake, E-mail: kitabatake{at}kais.kyoto-u.ac.jp


  Abstract

Lysozyme is one of the sweet-tasting proteins. To clarify the structure-sweetness relationship and the basicity-sweetness relationship in lysozyme, we have generated lysozyme mutants with Pichia systems. Alanine substitution of lysine residues demonstrated that two out of six lysine residues, Lys13 and Lys96, are required for lysozyme sweetness, while the remaining four lysine residues do not play a significant role in the perception of sweetness. Arginine substitution of lysine residues revealed that the basicity, but not the shape, of the side chain plays a significant role in sweetness. Single alanine substitutions of arginine residues showed that three arginine residues, Arg14, Arg21, and Arg73, play significant roles in lysozyme sweetness, whereas Arg45, Arg68, Arg125 and chemical modification by 1,2-cyclohexanedione did not affect sweetness. From investigation of the charge-specific mutations, we found that the basicity of a broad surface region formed by five positively charged residues, Lys13, Lys96, Arg14, Arg21, and Arg73, is required for lysozyme sweetness. Differences in the threshold values among sweet-tasting proteins might be caused by the broadness and/or the density of charged residues on the protein surface.

Keywords: basicity; lysozyme; mutation; Pichia pastoris; structure-function of sweet protein; sweet-tasting proteins.
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