Graduate student earns Schlumberger fellowship

Graduate
student earns Schlumberger fellowship
…………………………………………………………………

Developing enzymes
that make new natural products is the goal of this year’s
recipient of the Schlumberger Foundation Fellowship.

Mike Segura,
a graduate student in the Department of Chemistry, is studying
how plants make triterpenes — compounds that are useful
for medicinal and agricultural applications. He’s trying
to determine how synthases, or enzymes, that make triterpenes
form their complicated structures. By changing the sequence
of amino acids in these triterpene synthases, Segura can
make new compounds with different properties.

“The reactions
that triterpene synthases catalyze are so complicated that
chemists can’t do them without enzymes, and the best
way to make new triterpenes is to develop new triterpene
synthases,” said Segura, whose fourth year of graduate
study at Rice is being supported by the 2001-2002 Schlumberger
Foundation Fellowship.

The fellowship
is awarded each year to a student in the Wiess School of
Natural Sciences in mathematics, earth science, chemistry
or physics. Dean Kathleen Matthews selected Segura from
the students nominated by the department chairs in natural
sciences. Schlumberger Ltd., the second-largest provider
of oil-field services, funds the fellowship through a charitable
foundation it established in New York City.

Segura’s
approach has been to make large pools of mutant triterpene
synthases and then identify individual mutants that make
the desired compound. One such compound is lanosterol, a
steroid that yeast needs to make cell membranes. Another
is cycloartenol, a very complex molecule that is found only
in plants and that is required for plant growth.

Segura found
that a mutant of the enzyme that normally makes cycloartenol
can make lanosterol using a technique called genetic selection.
He put thousands of mutant cycloartenol synthases into a
yeast strain that needs lanosterol to live. These strains
were then grown without lanosterol, and only those that
acquired an enzyme that can make lanosterol lived. This
enabled Segura to sort the randomly generated mutant genes
to find amino acid combinations necessary to make lanosterol,
because only the yeast that can make lanosterol thrived.
Segura found the catalytic amino acid that caused the difference
by DNA sequencing. He is mutating this amino acid further
to make other compounds.

In a more complicated
method, Segura uses a technique known as “DNA shuffling”
to fragment two genes that perform different reactions,
mix the fragments and recombine them into millions of randomly
generated DNA combinations. Segura is looking for enzymes
that make lanosterol using the same genetic selection system
as before. “We created a new way to get yeast to grow
on cycloartenol, which is a non-natural compound to yeast
since it is made in plants,” Segura said. Using this
engineered yeast strain, he can genetically select mutant
triterpene synthases that make cycloartenol, even though
normal yeast can’t use cycloartenol for anything. He
gradually is zeroing in on the amino acids that produce
the triterpene. Once Segura finds the essential features,
he will begin studying what new and different reactions
they can be manipulated to perform.

“You have
to know what to change before you can change it,” he
said. “Right now I’m still trying to find out
which parts are relevant to the tinkering.”

Segura hopes
that his research will eventually lead to a way to get yeast
to modify compounds to have new properties. Many natural
products have interesting biological activities but cannot
be used for drugs because parts of their structures cause
undesired side effects. His thesis work to develop new ways
to alter natural product structures might eventually lead
to new drugs.

Segura’s
adviser, Seiichi Matsuda, is very enthusiastic about his
future.

“Mike is
extremely creative, but also gets things done efficiently
and with great technical expertise,” said Matsuda,
associate professor of chemistry and biochemistry and cell
biology. “This combination is rare and is the reason
that he is so productive. I am confident that he will succeed
at any level.”