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3-D STRUCTURE OF LIGHT-SENSING PROTEIN CONTROLS PROCESSES FROM SEED SPROUTING TO LEAF DROPPING
Plants use light not only for energy during photosynthesis, light also helps govern basic processes such as seed germination, growth, flowering, and, in autumn, dropping of leaves. Now, in the Nov. 17 issue of the journal Nature, scientists from the University of Wisconsin-Madison reveal the 3-D structure of the light-detecting protein, phytochrome. The team, funded mostly by the National Science Foundation, determined that phytochrome is twisted into a molecular knot, an uncommon shape for any protein. The scientists theorize the knot helps give phytochrome an overall stability as it snaps back and forth between two different forms in response to changes in light color. "Scientists have long known that this protein snaps back and forth between shapes in response to changes in light color," said Michael Mishkind, a program officer in NSF's biology directorate. "Now for the first time they have obtained a glimpse of the structure of this molecular switch at the atomic level." According to Mishkind, plants sense and interpret patterns of light quality and duration to ensure their life cycles and growth patterns stay in step with periodic and unexpected environmental changes. Phytochrome was discovered some 40 years ago by USDA scientists interested in the role light played in flowering and growth. Subsequent work showed that bacteria, fungi and plants all use phytochrome as a light-sensing protein to help guide development. Knowing the 3-D structure of phytochrome will allow researchers to determine the specific switching mechanism plants use to respond to light and how the light-derived signals are propagated within the plant. Nanotechnologists may also find a light-activated switch useful as they develop novel microscopic devices.
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