Contact: Robert Cahill
University of Texas Health Science Center at Houston
Biochemists manipulate fruit flavor enzymes
Would you like a lemony watermelon?
How about a strawberry-flavored banana? Biochemists at The University
of Texas Medical School at Houston say the day may be coming when
scientists will be able to fine tune enzymes responsible for flavors in
fruits and vegetables. In addition, it could lead to
environmentally-friendly pest control.
In the advance online publication of
on Aug. 20, UT Medical School Assistant Professor C.S. Raman, Ph.D.,
and his colleagues report 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.
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.
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.
"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 Rodney E. Kellems, Ph.D., professor and
chairman of the Department of Biochemistry & Molecular Biology at
the UT Medical School at Houston.
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."
study is titled "Structural insights into the evolutionary paths of
oxylipin biosynthetic enzymes." The lead authors were Dong-Sun Lee,
Ph.D., an assistant professor in the Department of Biochemistry &
Molecular Biology at the 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.
is supported by Pew Charitable Trusts through a Pew Scholar Award, The
Robert A. Welch Foundation, The National Institutes of Health, a
Beginning Grant in Aid from the American Heart Association, and an
INSERM Avenir Grant sponsored by La Fondation pour la Recherche