Chem. Senses 28: 491-498,
2003
© Oxford University Press 2003
Monkey Electrophysiological and Human Psychophysical Responses to Mutants of the Sweet Protein Brazzein: Delineating Brazzein Sweetness
? Department of Animal Health & Biomedical Sciences, University of Wisconsin—Madison, Madison, WI 53706, USA 1 Department of Biochemistry, University of Wisconsin—Madison, Madison, WI 53706, USA
Correspondence to be sent to: Göran Hellekant, Department of Animal Health & Biomedical Sciences, University of Wisconsin—Madison, Madison, WI 53706, USA. e-mail address: hellekant{at}svm.vetmed.wisc.edu
Responses to brazzein, 25 brazzein mutants and two forms of monellin were studied in two types of experiments: electrophysiological recordings from chorda tympani S fibers of the rhesus monkey, Macaca mulatta, and psychophysical experiments. We found that different mutations at position 29 (changing Asp29 to Ala, Lys or Asn) made the molecule significantly sweeter than brazzein, while mutations at positions 30 or 33 (Lys30Asp or Arg33Ala) removed all sweetness. The same pattern occurred again at the ß-turn region, where Glu41Lys gave the highest sweetness score among the mutants tested, whereas a mutation two residues distant (Arg43Ala) abolished the sweetness. The effects of charge and side chain size were examined at two locations, namely positions 29 and 36. The findings indicate that charge is important for eliciting sweetness, whereas the length of the side-chain plays a lesser role. We also found that the N- and C-termini are important for the sweetness of brazzein. The close correlation (r = 0.78) between the results of the above two methods corroborates our hypothesis that S fibers convey sweet taste in primates.
Key words: low-caloric natural sweeteners, Magnitude Labeled Scale, rhesus monkey, sweet taste receptor
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