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Many naturally occurring sweet-tasting proteins have been isolated and are largely expected to be available as a replacement for natural sugars and artificial sweeteners in the near future. We have carried out a large-scale all-electron quantum chemical calculation on des-pGlu brazzein, a sweet-tasting protein, and four different mutants by employing a density functional method program, ProteinDF, in order to examine a relationship between the sweetness of protein sweeteners and their electronic properties such as electrostatic potential and frontier molecular orbitals, HOMO and LUMO. ProteinDF all-electron canonical molecular orbital calculations toward des-pGlu brazzein and two different sweet-tatsting mutants, Asp29Lys and Glu41Lys, indicated that a number of amino acid residues including neutral amino acids, Tyr8 and Tyr51, have positive charge and especially for two mutants the positive charge widely spreads over each mutant. On the other hand, similar all-electron calculations for Arg33Ala and Arg43Ala mutants having a taste like water revealed that the number of amino acid residues with positive charge in these two mutants is less than that in des-pGlu brazzein and Asp29Lys and Glu41Lys mutants. In addition, we found that some positively charged amino acid residues occur in the HOMO and LUMO of des-pGlu brazzein and two sweet-tasting mutants.
Research papers (academic journals)
