title: Crystal structure of hyperthermophilic esterase EstE1 and the relationship between its dimerization and thermostability properties.
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-A resolution crystal structure of EstE1. The three-dimensional structure of EstE1 exhibits a classic alpha/beta 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 alpha/beta 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 beta8 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Biology, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, Korea. lovemilk99@yonsei.ac.kr <lovemilk99@yonsei.ac.kr>
authors.forename: Jung-Sue
authors.initials: JS
authors.lastname: Byun
authors.forename: Jin-Kyu
authors.initials: JK
authors.lastname: Rhee
authors.forename: Nam Doo
authors.initials: ND
authors.lastname: Kim
authors.forename: Jeonghyeok
authors.initials: J
authors.lastname: Yoon
authors.forename: Dong-Uk
authors.initials: DU
authors.lastname: Kim
authors.forename: Eunhee
authors.initials: E
authors.lastname: Koh
authors.forename: Jong-Won
authors.initials: JW
authors.lastname: Oh
authors.forename: Hyun-Soo
authors.initials: HS
authors.lastname: Cho
mesh_terms: D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D002942:Circular Dichroism; D003460:Crystallization; D018360:Crystallography, X-Ray; D019281:Dimerization; D004795:Enzyme Stability; D004950:Esterases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D011994:Recombinant Proteins; D004950:Esterases