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Chad A. Mirkin, Northwestern University, George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences. Photo by Bill Arsenault. 

DNA Blueprints Guide The Construction Of Specific Human Structures

Chad Mirkin discusses using DNA to build a three-dimensional structure out of gold, likening the process to building a house. Starting with basic materials such as bricks, wood, siding, stone and shingles, a construction team can build many different types of houses out of the same building blocks.
 
The article includes an audio recording of the full interview. Photo courtesy of the UCSD School of Medicine.
The Mutation Of Different Products From The Same Molecule Print E-mail
Science - Biological Sciences
TS-Si News Service   
Friday, 22 August 2008 16:30
Arabidopsis Thaliana
Arabidopsis thaliana
Arabidopsis plants from different geographical origins differ in many traits. 
 
The image shows schematically sequenced variation in plant DNA. 
 
Faster growth, darker leaves, and a different way of branching — wild varieties of this small mustard plant, Arabidopsis thaliana, are often substantially different from the laboratory strain.
 
A. thaliana is a favorite of many plant biologists and commonly used to test genetic questions.
 
The plant has been widely adopted by scientists as an easily manipulated model for other plants because it is simple to grow in the laboratory, has a short life cycle, and a small genome.
 
Compared to corn, which might have as many as 2.5 billion base pairs of DNA and the human genome with roughly 3 billion pairs, Arabidopsis only has about 120 million base pairs of DNA.
 
Research teams have investigated which detailed differences distinguish the genomes of strains from a wide variety of locations (the polar circle or the subtropics, from America, Africa or Asia).
 
The plant is self-pollinating and can produce many genetically identical offspring. Current reports date the start of this reproduction mode ("selfing") to at least a million years ago. 
 
Investigators have been surprised by the results: the extent of the genetic differences far exceeds expectations for such a streamlined genome.
 
These identical plants still have subtle individual differences (just like human twins). 
 
 
Houston, TX, USA. Cell biology explores how a single cell subdivides into different functions and organs. Understanding this process depends, in part, on understanding how molecular changes produce different products. New research demonstrates that the subtitution of a single amino acid can convert one enzyme into another.
 
Biochemists at The University of Texas (UT) Medical School at Houston have combined structural and evolutionary biology to draw new insights regarding enzyme function. Their demonstration shows how a single point mutation can contribute to the evolution of different biosynthetic pathways.
 
Structural insights into the evolutionary paths of oxylipin biosynthetic enzymes. Dong-Sun Lee, Pierre Nioche, Mats Hamberg & C. S. Raman. Nature, 2008. doi: 10.1038 / nature07307.
 
UT Medical School Assistant Professor C.S. Raman, Ph.D., and his colleagues have reported that they were able to manipulate flavor enzymes found in a popular plant model, Arabidopsis thaliana, by genetic means. The enzymes — allene oxide synthase (AOS) and hydroperoxide lyase (HPL) — produce jasmonate (responsible for the unique scent of jasmine flowers) and green leaf volatiles (GLV) respectively. GLVs confer characteristic aromas to fruits and vegetables.
 
Green leaf volatiles and jasmonates emitted by plants also serve to ward off predators. "Mind you plants can't run away from bugs and other pests. They need to deal with them. One of the things they do is to release volatile substances into the air so as to attract predators of the bugs," Raman said.
 
"Genetic engineering/modification (GM) of green leaf volatile production holds significant potential towards formulating environmentally friendly pest-control strategies. It also has important implications for manipulating food flavor," said Raman, the senior author. "For example, the aroma of virgin olive oil stems from the volatiles synthesized by olives. By modifying the activity of enzymes that generate these substances, it may be possible to alter the flavor of the resulting oils."
 
According to Raman, "Our work shows how you can convert one enzyme to another and, more importantly, provides the needed information for modifying the GLV production in plants." The scientists made 3-D images of the enzymes, which allowed them to make a small, but specific, genetic change in AOS, leading to the generation of HPL.
 
Illustration of allene oxide synthase (AOS) — an enzyme involved in the synthesis of jasmonate, which is responsible for the unique scent of jasmine flowers.
Illustration of allene oxide synthase (AOS) — an enzyme involved in the synthesis of jasmonate, which is responsible for the unique scent of jasmine flowers. Image courtesy of The University of Texas (UT) Medical School at Houston.
 
AOS and HPL are part of a super family of enzymes called cytochrome P450. P450 family enzymes are found in most bacteria and all known plants and animals. Although AOS or HPL are not found in humans, there are related P450 family members that help metabolize nearly half of the pharmaceuticals currently in use. In plants, AOS and HPL break down naturally-occurring, organic peroxides into GLV and jasmonate molecules. "Each flavor has a different chemical profile," Raman said.
 
Rodney E. Kellems, Ph.D., is professor and chairman of the Department of Biochemistry & Molecular Biology at the UT Medical School. According to Kellems, "A notable strength of this manuscript is the combined use of structural and evolutionary biology to draw new insights regarding enzyme function."
 
"These insights led to the striking demonstration that a single amino acid substitution converts one enzyme into another, thereby showing how a single point mutation can contribute to the evolution of different biosynthetic pathways. This begins to answer the long-standing question as to how the same starting molecule can be converted into different products by enzymes that look strikingly similar," said Keelems.
 
The study dispels the earlier view that these flavor-producing enzymes are only found in plants, Raman said. "We have discovered that they are also present in marine animals, such as sea anemone and corals. However, we do not know what they do in these organisms."
 


[N1] The research is supported by Pew Charitable Trusts through a Pew Scholar Award, The Robert A. Welch Foundation, The National Institutes of Health (NIH), a Beginning Grant in Aid from the American Heart Association (AHA), and an INSERM Avenir Grant sponsored by La Fondation pour la Recherche Medicale.

[N2]The lead authors were Dong-Sun Lee, Ph.D., an assistant professor in the Department of Biochemistry & Molecular Biology at The University of Texas (UT) Medical School at Houston, and Pierre Nioche, Ph.D., an assistant professor at the Université Paris Descartes. Mats Hamberg, M.D., Ph.D., professor of medical chemistry in the Division of Physiological Chemistry, Karolinska Institutet, Stockholm, Sweden, collaborated on the research.

 


Structural insights into the evolutionary paths of oxylipin biosynthetic enzymes. Dong-Sun Lee, Pierre Nioche, Mats Hamberg & C. S. Raman. Nature, 2008. doi: 10.1038 / nature07307.

Abstract

The oxylipin pathway generates not only prostaglandin-like jasmonates but also green leaf volatiles (GLVs), which confer characteristic aromas to fruits and vegetables. Although allene oxide synthase (AOS) and hydroperoxide lyase are atypical cytochrome P450 family members involved in the synthesis of jasmonates and GLVs, respectively, it is unknown how these enzymes rearrange their hydroperoxide substrates into different products. Here we present the crystal structures of Arabidopsis thaliana AOS, free and in complex with substrate or intermediate analogues. The structures reveal an unusual active site poised to control the reactivity of an epoxyallylic radical and its cation by means of interactions with an aromatic -system. Replacing the amino acid involved in these steps by a non-polar residue markedly reduces AOS activity and, unexpectedly, is both necessary and sufficient for converting AOS into a GLV biosynthetic enzyme. Furthermore, by combining our structural data with bioinformatic and biochemical analyses, we have discovered previously unknown hydroperoxide lyase in plant growth-promoting rhizobacteria, AOS in coral, and epoxyalcohol synthase in amphioxus. These results indicate that oxylipin biosynthetic genes were present in the last common ancestor of plants and animals, but were subsequently lost in all metazoan lineages except Placozoa, Cnidaria and Cephalochordata.

 
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Last Updated on Friday, 22 August 2008 18:38