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Updated: Jul 27, 2026

A New Screening Method for the Directed Evolution of Thermostable Bacteriolytic Enzymes
Published on: November 7, 2012
Two flexible loops in subtilisin-like thermophilic protease, thermicin, from Thermoanaerobacter yonseiensis
Hyeung Jin Jang1, Chang-Hun Lee, Weontae Lee
1Department of Biochemistry, College of Science, Protein Network Research Center, Yonsei University, Seoul 120-749, Korea.
Abstract:
A gene that encodes a thermostable protease, coined thermicin, has been isolated from Thermoanaerobacter yonseiensis that is expressed and characterized in E. coli. In order to elucidate the molecular characteristics on thermostability of the enzyme, molecular modeling and mutagenesis technology were applied. In the modeling structure, the structural core, including the active site, was well conserved; whereas, the two loop regions were unique when compared to thermitase. The mutant enzyme with the small loop deleted (D190-I196), based on modeling structural information, showed identical enzyme activity. However, when the large loop was deleted (P233-P244), a little lower K(m) and even a lower kcat was found. This indicates that the large loop could influence catalytic activity. However, the unfolding temperature (T(m)), which was determined by a differential-scanning calorimetry for the mutant enzyme deleted the small loop, was 96 degrees C. This is 14 degrees C lower than that for the parent thermicin. These results suggest that the small loop may play a role in maintaining the proper folding of the enzyme at high temperatures, whereas the large loop might be related to catalysis.
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