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The esterase from the thermophilic eubacterium Bacillus acidocaldarius : Structural‐functional relationship and comparison with the esterase from the hyperthermophilic archaeon Archaeoglobus fulgidus
Author(s) -
D'Auria Sabato,
Herman Petr,
Lakowicz Joseph R.,
Tanfani Fabio,
Bertoli Enrico,
Manco Giuseppe,
Rossi Mose'
Publication year - 2000
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/1097-0134(20000815)40:3<473::aid-prot140>3.0.co;2-8
Subject(s) - esterase , thermophile , sulfolobus acidocaldarius , chemistry , enzyme , biochemistry , active site , archaea , gene
The esterase from the thermophilic eubacterium Bacillus acidocaldarius is a thermophilic and thermostable monomeric protein with a molecular mass of 34 KDa. The enzyme, characterized as a “B‐type” carboxylesterase, displays the maximal activity at 65°C. Interestingly, it is also quite active at room temperature, an unusual feature for an enzyme isolated from a thermophilic microorganism. We investigated the effect of temperature on the structural properties of the enzyme, and compared its structural features with those of the esterase from the hyperthermophilic archaeon Archaeoglobus fulgidus . In particular, the secondary structure and the thermal stability of the esterase were studied by FT‐IR spectroscopy, while information on the conformational dynamics of the enzyme were obtained by frequency‐domain fluorometry and anisotropy decays. Our data pointed out that the Bacillus acidocaldarius enzyme possesses a secondary structure rich in α‐helices as described for the esterase isolated from Archaeoglobus fulgidus . Moreover, infrared spectra indicated a higher accessibility of the solvent ( 2 H 2 O) to Bacillus acidocaldarius esterase than to Archaeoglobus fulgidus enzyme suggesting, in turn, a less compact structure of the former enzyme. The fluorescence studies showed that the intrinsic tryptophanyl fluorescence of the Bacillus acidocaldarius protein was well represented by the three‐exponential model, and that the temperature affected the protein conformational dynamics. The data suggested an increase in the protein flexibility on increasing the temperature. Moreover, comparison of Bacillus acidocaldarius esterase with the Archaeoglobus fugidus enzyme fluorescence data indicated a higher flexibility of the former enzyme at all temperatures tested, supporting the infrared data and giving a possible explanation of its unusual relative high activity at low temperatures. Proteins 2000;40:473–481. © 2000 Wiley‐Liss, Inc.