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Plant Enzyme Turns Scientists' Thoughts to Taxol

By Jan Suszkiw
July 27, 2004

A synthetic peptide fashioned after a natural plant enzyme has surprised Agricultural Research Service scientists with its taxol-like ability to curtail abnormal cell growth in test tubes.

ARS plant physiologist Steven Huber and colleagues originally created the peptide "SS2" to help study sucrose synthase, an enzyme that metabolizes sugar and delivers carbon for cellular growth and other uses. One approach involved using SS2 to identify regions of sucrose synthase that bind to actin, a filamentous protein comprising part of the "cytoskeleton" that plant cells use when dividing and elongating.

Eventually, such investigations may yield clues to increasing cellular use of carbon for seed storage products like starch, oil and protein in crops, according to Huber, at the ARS Photosynthesis Research Unit, Urbana, Ill. He's working with Heike Winter, an assistant professor at the University of North Carolina (UNC), Raleigh, and Carolyn Larabell, a cell biologist at the Lawrence Berkeley National Laboratory, Berkeley, Calif.

During their studies, the team observed that SS2 caused actin filaments to clump together, a phenomenon called "bundling" that stops plant cells from dividing. Bundling is similar to how taxol, a yew tree derivative, checks the spread of some human cancer cells. Key differences--including ease of synthesis, water solubility and rapid degradation--led the team to wonder whether SS2 could mimic taxol's therapeutic powers, possibly without some of the drug's side effects, such as reduced blood counts, and cost.

As a preliminary step to finding out, Larabell designed test tube experiments in which she infused frog eggs and tumor cells with SS2. As in plants, SS2 caused actin bundling in the cell cultures, halting their division and movement in the case of tumor cells. In another experiment, SS2 prevented the formation of "actin comet tails," which Listeria monocytogenes bacteria use to rapidly travel through cells in the human body, causing sickness.

The Berkeley lab, a coapplicant with ARS and UNC on a patent for SS2, is seeking a licensing partner to investigate the peptide's potential medical applications. Meanwhile, the team's plant carbon studies continue.

ARS is the U.S. Department of Agriculture's chief scientific research agency.