Research article

Crystal structure of hyperthermophilic esterase EstE1 and the relationship between its dimerization and thermostability properties

Jung-Sue Byun¹ , Jin-Kyu Rhee² , Nam Doo Kim³ , JeongHyeok Yoon³ , Dong-Uk Kim¹ , Eunhee Koh¹ , Jong-Won Oh² and Hyun-Soo Cho¹

¹  Department of Biology, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749, Korea

²  Department of Biotechnology, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749, Korea

³  Drug Discovery R&D Center, Equispharm Co., Ltd., Sungnam 463-020, Korea

author email corresponding author email

BMC Structural Biology 2007, 7:47doi:10.1186/1472-6807-7-47

Published:	12 July 2007

Abstract

Background

EstE1 is a hyperthermophilic esterase belonging to the hormone-sensitive lipase family and was originally isolated by functional screening of a metagenomic library constructed from a thermal environmental sample. Dimers and oligomers may have been evolutionally selected in thermophiles because intersubunit interactions can confer thermostability on the proteins. The molecular mechanisms of thermostabilization of this extremely thermostable esterase are not well understood due to the lack of structural information.

Results

Here we report for the first time the 2.1-Å resolution crystal structure of EstE1. The three-dimensional structure of EstE1 exhibits a classic α/β hydrolase fold with a central parallel-stranded beta sheet surrounded by alpha helices on both sides. The residues Ser154, Asp251, and His281 form the catalytic triad motif commonly found in other α/β hydrolases. EstE1 exists as a dimer that is formed by hydrophobic interactions and salt bridges. Circular dichroism spectroscopy and heat inactivation kinetic analysis of EstE1 mutants, which were generated by structure-based site-directed mutagenesis of amino acid residues participating in EstE1 dimerization, revealed that hydrophobic interactions through Val274 and Phe276 on the β8 strand of each monomer play a major role in the dimerization of EstE1. In contrast, the intermolecular salt bridges contribute less significantly to the dimerization and thermostability of EstE1.

Conclusion

Our results suggest that intermolecular hydrophobic interactions are essential for the hyperthermostability of EstE1. The molecular mechanism that allows EstE1 to endure high temperature will provide guideline for rational design of a thermostable esterase/lipase using the lipolytic enzymes showing structural similarity to EstE1.