'Marriage' makes sugary bands stay sweet.

'Marriage' makes sugary bands stay sweet

Over the last five years, Sung-Hou Kim and his co-workers at the University of California, Berkeley, have identified the three-dimensional structure of a pair of sugary compounds. Derived from African berries, each is about 100,000 times sweeter than sucrose. The larger compound, called thaumatin-1 (SN: 3/23/85, p.186), recently won FDA approval for use in chewing gum. But Kim says thaumatin's unwieldy size complicates genetic tinkering to overcome certain drawbacks, such as its permanent loss of sweetness when heated.

Monellin, its far smaller chemical cousin, has proved more adaptable. In its natural form, monellin loses sweetness during heating because its two interlacing strings of amino acids are unbound and tend to separate at high temperatures. But Kim's team has inserted genes for a mutant version of monellin -- in which the two adjacent loose ends (see arrow) are bound -- into microbes. He now reports that the microbially produced, single-stranded monellin has a three-dimensional structure that allows it to recover its shape and sweetness after heating.