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Perspectives on biological catalysis

Published on October 1, 2007 Updated on July 31, 2017   48 min

A selection of talks on Biochemistry

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0:00
I am Stephen Benkovic, and I hold the Eberly Chair in Chemistry at Penn State. To begin, I'd like to update my previous lecture on biological catalysis. I plan to review sufficient background material to serve as a basis for my discussion of the recent advances that have further informed this topic.
0:22
The illustration presents the reaction cycle for DHFR. More about that later. A feature of enzymes is their rate accelerations relative to their reaction solution counterpart, with their ratios being in the millions. I wish to explore three questions. They are: how do enzyme motions and fluctuations impact catalysis? We know that the structures of enzymes are dynamic, but how do these dynamic features actually impact catalysis? Are the timescales for protein structural changes and the enzymatic catalytic cycle similar? We will review the timescales for protein motions in a later slide. The third question is, how are electrostatics modulated in enzyme active sites in conjunction with catalysis? Such interactions long had been implicated in catalysis, but how are they optimized? Remember, we still view catalysis in terms of transition state theory. The key being, selective stabilization of the transition state, lowering the free energy barrier that, in turn, translates into an increased reaction rate.
1:35
Our paradigm is dihydrofolate reductase, DHFR. The reaction it catalyzes is the conversion of dihydrofolate, shown in the box, through the agency of NADPH to give you reduced tetrahydrofolate, H4F, and NADP plus product. This transformation maintains levels of tetrahydrofolate required for biosynthesis of purines, pyrimidines, and amino acids that are key for cellular viability. Consequently, inhibitors have been found, such as methotrexate and trimethoprim, for treating cancer, bacterial infections, and rheumatoid arthritis, with this enzyme clearly being the pharmacological target. Our work in DHFR has been accomplished through many collaborations. We have an excellent network of collaborators whose names are listed in this slide. References to our joint publications can be found at the end of this lecture.