Plant enzyme's origins traced to non-enzyme ancestors
Date: 20.8.2012
(Phys.org) -- As plants began to transition from aquatic habitats to dry land some 500 million years ago, their needs changed. Those primitive ancestors of modern plants were ill-equipped to survive in a dry, sunlight-blasted world. But gradually, they evolved enzymes that let them synthesize new kinds of chemicals to protect them from the threats of their new world, such as the damaging ultraviolet (UV) rays of the sun.
A new study from Howard Hughes Medical Institute investigator Joseph P. Noel and his colleagues focuses on one of those metabolic enzymes, which today is so efficient at doing its job it is considered by biochemists to be catalytically "perfect." In a paper published online May 13, 2012, in the journal Nature, the researchers lay out evidence for how that enzyme evolved from its non-catalytic ancestor proteins. Noel, who is at the Salk Institute for Biological Studies, is interested in understanding how today's plants acquired the ability to produce a diverse chemical arsenal - hundreds of thousands of specialized molecules that let plants flourish in varied and sometimes hostile environments around the world. Many of those chemicals are also useful to humans - as drugs, nutrients for disease prevention, flavors, dyes, and pesticides. The enzymatic tools deployed by modern plants must have evolved from protein molecules that ancient plants used to survive in a very different world, Noel explains. For the current study, Noel and his colleagues at the Salk Institute, together with collaborators at Iowa State University, focused on an enzyme called chalcone isomerase (CHI), which is critical to the production of the specialized metabolites known as flavonoids. Flavonoids, which come in thousands of forms, provide plants with color to attract pollinators, noxious scents to repel herbivores, odd tastes to discourage fungi colonization, and protectants against the bleaching effects of the sun's UV light. Biochemists have long described CHI as a "perfect" enzyme because its atomic structure is so finely tuned for catalyzing reactions with extreme speed. "As fast as chemicals bump into it in solution or in the cytoplasm of plant cells, CHI makes a flavonoid product," Noel explains. "In an evolutionary sense, it's reached its limit. It's going as fast as it can." ...
