Segura Secures Schlumberger Fellowship

Mike Segura’s goal of developing enzymes that make new natural products has earned him this year’s Schlumberger Foundation Fellowship.

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 2001–02 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. Because only the yeast that can make lanosterol thrived, Segura was able to sort the randomly generated mutant genes to find amino acid combinations necessary to make lanosterol. 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 nonnatural 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’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.”

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 work to develop new ways to alter natural product structures might eventually lead to new drugs.