Communications
DOI: 10.1002/anie.200806276
Divergent Evolution
Converting an Esterase into an Epoxide Hydrolase**
Helge Jochens, Konstanze Stiba, Christopher Savile, Ryota Fujii, Juin-Guo Yu,
Tatsiana Gerassenkov, Romas J. Kazlauskas,* and Uwe T. Bornscheuer*
Dedicated to Professor Kalle Hult on the occasion of his 65th birthday
Divergent evolution has created superfamilies of enzymes
with the same protein fold, but different catalytic abilities. For
example, the a/b-hydrolase superfamily[1] enzymes all cata-
also introduced enzymatic activity into non-catalytic proteins,
but these experiments all required extensive substitutions.[12]
Herein, we test the hypothesis that a few amino acid
substitutions are sufficient to interconvert the catalytic
abilities of different enzymes within the a/b-hydrolase
family. Our test case is to convert an esterase from Pseudo-
monas fluorescens (PFE) into an epoxide hydrolase. Mech-
anistic considerations suggest that two or three amino acid
substitutions could convert an esterase mechanism into an
epoxide hydrolase mechanism (Scheme 1). Esterases have a
Ser-His-Asp catalytic triad,[13] whereas epoxide hydrolases
use an Asp-His-Asp triad,[14] so one substitution is needed in
the triad. In addition, epoxide hydrolases contain two
tyrosines to protonate the epoxide oxygen during catalysis,
which are two more substitutions. In one case, only one of
these tyrosines was essential to catalysis,[15] so perhaps only
one is needed.
lyze reactions involving
a
nucleophilic attack: ester,[2]
amide,[3] epoxide,[4] and alkyl halide hydrolysis,[5] cyanide
addition to aldehydes forming a carbon–carbon bond[6] as well
as several others. Many of these enzymes, and especially
lipases and esterases, accept a wide range of substrates, each
with high stereoselectivity, making them versatile catalysts for
organic synthesis.[2,7]
The different catalytic abilities require distinct mechanis-
tic steps, but some of these mechanistic steps may be shared.
X-ray crystallography and biochemical studies suggest that
the new mechanistic steps require only a few amino acid
substitutions, but the amino acid sequences of enzymes within
a superfamily differ by hundreds of substitutions and possible
insertions and deletions.
Previous reports that involved changing the catalytic
activity of an enzyme required different approaches. Chang-
ing from hydrolysis of a thioester to hydrolysis of a b-lactam
required insertion, deletion, and substitution of loops as well
as amino acid substitutions.[8] Changing 4-chlorobenzoyl-CoA
dehalogenase to a crotonase activity required eight amino
acid substitutions.[9] However, in a few cases, a single amino
acid substitution could introduce new catalytic activity: from
a racemase to an aldolase, from an esterase to a perhydrolase,
from an epimerase to an o-succinylbenzoate synthase, and
from a decarboxylase to a racemase.[10,11] Researchers have
To identify the positions of these residues within the PFE
we compared the structures and amino acid sequences of six
epoxide hydrolases (PDB entries: 2E3J, 2CJP, 1S8O, 1CQZ,
1EHY, and 1Q07) with three esterases (PDB entries: 1VA4,
1P0, and 1ZOI) using clustalw.[17] This comparison (Figure 1)
identified the position of the catalytic nucleophile (D94), four
possible positions for the two mechanistically important
tyrosines (Y125, Y139, Y143, Y195) and three further
amino acids that are conserved in epoxide hydrolases but
are missing from PFE (P29, H93, K188). The position of one
of these tyrosines was identified as being at amino acid 195,
but as it was not definitely clear where to introduce the
second tyrosine, it was placed at all three alternative positions.
Consequently, the following mutants were created by Quik-
Change site-directed mutagenesis and expressed recombi-
nantly in E. coli: M1: S94D; M2: S94D, F125Y, V195Y; M3:
S94D, F143Y, V195Y; M4: S94D, F125Y, F143Y, V195Y; M5:
L29P, S94D, F125Y, K188M; M6: L29P, S94D, F125Y, V195Y;
M7: L29P, F93H, S94D, F125Y, V139Y, V195Y. As expected,
all mutants showed no esterase activity against p-nitrophenyl
acetate above background levels (< 10 mUmgÀ1), as the
catalytic nucleophile was replaced by an aspartate. Unfortu-
nately, all these mutants also showed no detectable epoxide
hydrolase activity towards p-nitrostyrene oxide (see Support-
ing Information).
[*] Dr. C. Savile, Dr. R. Fujii, J.-G. Yu, T. Gerassenkov,
Prof. R. J. Kazlauskas
University of Minnesota, Department of Biochemistry, Molecular
Biology & Biophysics
1479 Gortner Avenue, 174 Gortner Lab, St. Paul, MN 55108 (USA)
Fax: (+1)612-625-5780
E-mail: rjk@umn.edu
Dipl.-Biochem. H. Jochens, Dr. K. Stiba, Prof. Dr. U. T. Bornscheuer
Institute of Biochemistry, Dept. of Biotechnology & Enzyme
Catalysis, University of Greifswald
Felix-Hausdorff-Strasse 4, 17487 Greifswald (Germany)
Fax: (+49)3834-86-80066
E-mail: uwe.bornscheuer@uni-greifswald.de
[**] We thank Prof. Dick Janssen for providing the gene of Agrobacterium
radiobacter epoxide hydrolase and Dr. Santosh Padhi for preparation
of several site-directed mutants. U.T.B. thanks the German Research
Foundation (DFG, grant Bo1862/4-1), and R.J.K. the US National
Science Foundation (CHE-0616560) for financial support.
Because it was not obvious why the created mutants failed
to catalyze the reaction, we applied directed evolution to
search for missing key amino acids that correct the imperfect
geometry. Starting from mutants M4–M6, we created a
mutant library by a error-prone polymerase chain reaction
(epPCR) and selected active variants using a growth assay.[18]
Supporting information for this article is available on the WWW
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Angew. Chem. Int. Ed. 2009, 48, 3532 –3535