Being many thousands of times sweeter than
sucrose on a molar basis, monellin has significant
potential as an alternative to carbohydrate or artificial
sweeteners because it combines a marked persistence of taste sensation
with a very low caloric power. However, thermal denaturation
of monellin, which occurs when the protein is heated
above 50 C, leads to a loss of sweetening power, clearly indicating
that a correctly folded three-dimensional structure is a prerequisite
for sweetness. To enhance the thermal stability of monellin,
recombinant single chain constructs, obtained by joining the two
chains either by a direct amide bond (SCM) or by the insertion of a dipeptide linker (MNEI)were generated,
and found to be as sweet as native monellin, but endowed
with increased thermal stability. Both single chain constructs refold easily even after boiling
at low pH and remain potently sweet as wild type monellin.