QS-21 is one of the few FDA-approved adjuvants: molecules that improve vaccine effectiveness by boosting the overall immune response. QS-21 is traditionally harvested from trees—the 21st fraction of Quillaja saponaria soapbark tree extract, to be exact—and obtaining the molecule is both arduous and ecologically damaging. To make QS-21 more accessible, assistant chemistry professor Yuzhong Liu, PhD, who recently joined Scripps Research, harnessed her background in synthetic biology to produce this highly sought-after molecule in yeast. These findings from her postdoctoral work at the University of California, Berkeley were published in Nature in May 2024.