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Biophysical characterization of mutants of Bacillus subtilis lipase evolved for thermostability: Factors contributing to increased activity retention
Author(s) -
Augustyniak Wojciech,
Brzezinska Agnieszka A.,
Pijning Tjaard,
Wienk Hans,
Boelens Rolf,
Dijkstra Bauke W.,
Reetz Manfred T.
Publication year - 2012
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.2031
Subject(s) - thermostability , bacillus subtilis , lipase , circular dichroism , mutant , enzyme , chemistry , biochemistry , directed evolution , biophysics , crystallography , biology , bacteria , genetics , gene
Previously, Lipase A from Bacillus subtilis was subjected to in vitro directed evolution using iterative saturation mutagenesis, with randomization sites chosen on the basis of the highest B‐factors available from the crystal structure of the wild‐type (WT) enzyme. This provided mutants that, unlike WT enzyme, retained a large part of their activity after heating above 65°C and cooling down. Here, we subjected the three best mutants along with the WT enzyme to biophysical and biochemical characterization. Combining thermal inactivation profiles, circular dichroism, X‐ray structure analyses and NMR experiments revealed that mutations of surface amino acid residues counteract the tendency of Lipase A to undergo precipitation under thermal stress. Reduced precipitation of the unfolding intermediates rather than increased conformational stability of the evolved mutants seems to be responsible for the activity retention.