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Expression and properties of the highly alkalophilic phenylalanine ammonia-lyase of thermophilic Rubrobacter xylanophilus.
[phenylketonuria]
The
sequence
of
a
phenylalanine
ammonia-lyase
(
PAL
;
EC
:
4
.
3
.
1
.
24
)
of
the
thermophilic
and
radiotolerant
bacterium
Rubrobacter
xylanophilus
(
RxPAL
)
was
identified
by
screening
the
genomes
of
bacteria
for
members
of
the
phenylalanine
ammonia-lyase
family
.
A
synthetic
gene
encoding
the
RxPAL
protein
was
cloned
and
overexpressed
in
Escherichia
coli
TOP
10
in
a
soluble
form
with
an
N-
terminal
His
6
-
tag
and
the
recombinant
RxPAL
protein
was
purified
by
Ni-
NTA
affinity
chromatography
.
The
activity
assay
of
RxPAL
with
l-phenylalanine
at
various
pH
values
exhibited
a
local
maximum
at
pH
8
.
5
and
a
global
maximum
at
pH
11
.
5
.
Circular
dichroism
(
CD
)
studies
showed
that
RxPAL
is
associated
with
an
extensive
α-helical
character
(
far
UV
CD
)
and
two
distinctive
near-
UV
CD
peaks
.
These
structural
characteristics
were
well
preserved
up
to
pH
11
.
0
.
The
extremely
high
pH
optimum
of
RxPAL
can
be
rationalized
by
a
three
-dimensional
homology
model
indicating
possible
disulfide
bridges
,
extensive
salt
-bridge
formation
and
an
excess
of
negative
electrostatic
potential
on
the
surface
.
Due
to
these
properties
,
RxPAL
may
be
a
candidate
as
biocatalyst
in
synthetic
biotransformations
leading
to
unnatural
l-
or
d-amino
acids
or
as
therapeutic
enzyme
in
treatment
of
phenylketonuria
or
leukemia
.
