Scientists link enzyme to
life forms
By Russ Brickey
Staff
Writer
Purdue University scientists have discovered an
important link between a 3 billion-year-old enzyme and the early stages
of life on earth. This ancient enzyme may help scientists control greenhouse
gasses in the future.
Assistant professors David Sanders and Miriam Hasson,
a husband and wife team in the department of biological sciences, have
created a three-dimensional computer model of the enzyme acetate kinase,
which is an important building-block in the evolution of protein based
life forms.
"It’s hard to imagine life evolving anything
like it’s like without acetate enzymes," Sanders said.
Enzymes are protein catalysts found in all living
cells that allow the cells to utilize their energy currency and make
life possible.
Acetate kinase, a molecule found in bacteria, is
part of an ancient family of enzymes likely to have been among the first
"activated" molecules utilized by living cells. This means
that acetate kinase was perhaps one of the crucial building blocks in
the evolutionary process.
Acetate kinase allows scientists a "unique
opportunity to look at how protein based life works," said Sanders.
The structure of acetate kinase suggests that it
may be the ancestor of other enzymes known as kinases, or phosphotransferases,
which are used by living organisms for cell movement, muscle movement
and the metabolism of glucose.
According to Sanders and Hasson, acetate kinase
appears to have been active at a point in evolutionary history when
protein-based life was first developing.
The link between early life and acetate kinase
was first realized when Sanders and Hasson predicted the structure of
the enzyme based on the structures of certain proteins, despite the
fact that the amino-acid sequence was unlike any known structure.
Hasson, a crystologist who reconstructs microcosmic
crystal structures on a computer, created a three-dimensional model
of an enzyme.
By comparing the structure of acetate kinase to
other enzyme structures found in the enzyme "super-family,"
Hasson and Sanders were able to establish the link between acetate kinase
and early life.
"It was doing that structure that made it
obvious how it worked in the history of evolution," Sanders said.
"It gives a really unique chance to paint a family portrait."
Knowing the structure of acetate kinase also makes
it possible to study relationships within the enzyme family.
"It’s like describing the hair color
of relatives," Hasson said, like comparing the folds and shapes
of different enzymes to the genetically passed down trait. By looking
at the similarities and differences between enzyme cousins, scientists
are able to establish an enzyme family.
The enzyme may also allow scientists to control
the output of greenhouses gases in the future.
Acetate kinase is found in a bacterium that is
responsible for one-third of the world’s methane, a green house
gas. By understanding its structure, scientists may be able to control
the enzyme and create bacteria that will eliminate the gas produced
by organic waste, thereby reducing the overall methane entering Earth’s
atmosphere.
Establishing the structure of acetate kinase has
the potential of being a major discovery. "It is so much fun,"
Hasson said. "It is one of the best things you can do."
The enzyme was first purified by a Penn State scientist,
James G. Ferry, who shares credit for the discovery.
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