Rare Diseases Symptoms Automatic Extraction
Home
A random Abstract
Our Project
Our Team
Molecular mechanisms leading to three different phenotypes in the cblD defect of intracellular cobalamin metabolism.
[homocystinuria without methylmalonic aciduria]
The
cblD
defect
of
intracellular
vitamin
B
(
12
)
metabolism
can
lead
to
isolated
methylmalonic
aciduria
(
cblD-MMA
)
or
homocystinuria
(
cblD-HC
)
,
or
combined
methylmalonic
aciduria
and
homocystinuria
(
cblD-MMA
/
HC
)
.
We
studied
the
mechanism
whereby
MMADHC
mutations
can
lead
to
three
phenotypes
.
The
effect
of
various
expression
vectors
containing
MMADHC
modified
to
contain
an
enhanced
mitochondrial
leader
sequence
or
mutations
changing
possible
downstream
sites
of
reinitiation
of
translation
or
mutations
introducing
stop
codons
on
rescue
of
adenosyl-
and
methylcobalamin
(
MeCbl
)
formation
was
studied
.
The
constructs
were
transfected
into
cell
lines
derived
from
various
cblD
patient
's
fibroblasts
.
Expression
of
10
mutant
alleles
from
15
cblD
patients
confirmed
that
the
nature
and
location
of
the
mutations
correlate
with
the
biochemical
phenotype
.
In
cblD-MMA
/
HC
cells
,
improving
mitochondrial
targeting
of
MMADHC
clearly
increased
the
formation
of
adenosylcobalamin
(
AdoCbl
)
with
a
concomitant
decrease
in
MeCbl
formation
.
In
cblD-MMA
cells
,
this
effect
was
dependent
on
the
mutation
and
showed
a
negative
correlation
with
endogenous
MMADHC
mRNA
levels
.
These
findings
support
the
hypothesis
that
a
single
protein
exists
with
two
different
functional
domains
that
interact
with
either
cytosolic
or
mitochondrial
targets
.
Also
a
delicate
balance
exists
between
cytosolic
MeCbl
and
mitochondrial
AdoCbl
synthesis
,
supporting
the
role
of
cblD
protein
as
a
branch
point
in
intracellular
cobalamin
trafficking
.
Furthermore
,
our
data
indicate
that
the
sequence
after
Met
116
is
sufficient
for
MeCbl
synthesis
,
whereas
the
additional
sequence
between
Met
62
and
Met
116
is
required
for
AdoCbl
synthesis
.
Accordingly
,
western
blot
studies
reveal
proteins
of
the
size
expected
from
the
stop
codon
position
with
subsequent
reinitiation
of
translation
.