Sweetness and sweeteners - Neoculin, a taste-modifying protein

5 important questions on Sweetness and sweeteners - Neoculin, a taste-modifying protein

What is neoculin (NCL)?

NCL is a heterodimeric protein, containing an acidic and a basic subunit (curculin).

How can NCL activate the T1R2/T1R3 receptors?

In a pH-dependent manner.
  • at acidic pH --> cells are activated and the compound is perceived as sweet
  • neutral pH --> no activity, no sweetness

Which amino acid residues cause the activity of NCL?

Histidine residues. NCL has 5.
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What happens to NCL at acidic pH?

  • Histidine, arginine and lysine --> protonated and positively charged
  • Aspartic acid and glutamic acid --> protonated and neutral
  • The positive charges in the heterodimer induce electrostatic repulsion, and the protein is thought to obtain an open conformation.

What happens to NCL at neutral pH?

  • Histidine --> lost positive charge and is neutral
  • Arginine and lysine --> positive charge
  • Aspartic acid and glutamic acid --> lose their proton, negatively charged
  • More attraction between the subunits.
  • The protein adopts the closed conformation.

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