bioRxiv (Cold Spring Harbor Laboratory),
Год журнала:
2023,
Номер
unknown
Опубликована: Дек. 22, 2023
Abstract
The
protein
translocon
at
the
endoplasmic
reticulum
comprises
Sec61
translocation
channel
and
numerous
accessory
factors
that
collectively
facilitate
biogenesis
of
secretory
membrane
proteins.
Here,
we
leveraged
recent
advances
in
cryo-EM
structure
prediction
to
derive
insights
into
several
novel
configurations
ribosome-translocon
complex.
We
show
how
a
transmembrane
domain
(TMD)
looped
configuration
passes
through
lateral
gate
during
insertion;
nascent
chain
can
bind
constrain
conformation
ribosomal
uL22;
translocon-associated
(TRAP)
complex
adjust
its
position
different
stages
biogenesis.
Most
unexpectedly,
find
large
proportion
complexes
contains
RAMP4
intercalated
Sec61’s
gate,
widening
central
pore
contributing
hydrophilic
interior.
These
structures
lead
mechanistic
hypotheses
for
function
highlight
remarkably
plastic
machinery
whose
conformations
composition
dynamically
diverse
range
substrates.
Trends in Biochemical Sciences,
Год журнала:
2023,
Номер
49(2), С. 105 - 118
Опубликована: Ноя. 1, 2023
Ribosomes
interact
with
a
variety
of
different
protein
biogenesis
factors
that
guide
newly
synthesized
proteins
to
their
native
3D
shapes
and
cellular
localization.
Depending
on
the
type
translated
substrate,
distinct
set
cotranslational
must
ribosome
in
timely
coordinated
manner
ensure
proper
biogenesis.
While
cytonuclear
require
maturation
folding
factors,
secretory
be
maintained
an
unfolded
state
processed
cotranslationally
by
transport
membrane
translocation
factors.
Here
we
explore
specific
processing
steps
for
cytonuclear,
secretory,
eukaryotes
then
discuss
how
nascent
polypeptide-associated
complex
(NAC)
sorts
these
into
correct
pathway.
During
cotranslational
translocation,
the
signal
peptide
of
a
nascent
chain
binds
Sec61
translocon
to
initiate
protein
transport
through
endoplasmic
reticulum
(ER)
membrane.
Our
cryo-electron
microscopy
structure
ribosome-Sec61
shows
binding
an
ordered
heterotetrameric
translocon-associated
(TRAP)
complex,
in
which
TRAP-γ
is
anchored
at
two
adjacent
positions
28
PLoS Biology,
Год журнала:
2023,
Номер
21(4), С. e3001995 - e3001995
Опубликована: Апрель 20, 2023
Cotranslational
modification
of
the
nascent
polypeptide
chain
is
one
first
events
during
birth
a
new
protein.
In
eukaryotes,
methionine
aminopeptidases
(MetAPs)
cleave
off
starter
methionine,
whereas
N-acetyl-transferases
(NATs)
catalyze
N-terminal
acetylation.
MetAPs
and
NATs
compete
with
other
cotranslationally
acting
chaperones,
such
as
ribosome-associated
complex
(RAC),
protein
targeting
translocation
factors
(SRP
Sec61)
for
binding
sites
at
ribosomal
tunnel
exit.
Yet,
well-resolved
structures
ribosome-bound
RAC,
SRP
Sec61,
are
available,
structural
information
on
mode
ribosome
interaction
eukaryotic
or
five
active
only
available
NatA.
Here,
we
present
cryo-EM
yeast
Map1
NatB
bound
to
ribosome-nascent
complexes.
mainly
associated
dynamic
rRNA
expansion
segment
ES27a,
thereby
kept
an
ideal
position
below
exit
act
emerging
substrate
chain.
For
NatB,
observe
two
copies
complex.
NatB-1
binds
directly
exit,
again
involving
NatB-2
located
second
universal
adapter
site
(eL31
uL22).
The
complexes
differs
but
overlaps
that
NatA
Map1,
implying
exclusively
We
further
ES27a
adopts
distinct
conformations
when
NatA,
together
suggesting
contribution
coordination
sequential
activity
these
tunnel.
The Journal of Cell Biology,
Год журнала:
2025,
Номер
224(4)
Опубликована: Март 6, 2025
Most
of
the
mitochondria
proteome
is
nuclear-encoded,
synthesized
by
cytoplasmic
ribosomes,
and
targeted
to
posttranslationally.
However,
a
subset
mitochondrial-targeted
proteins
imported
co-translationally,
although
molecular
mechanisms
governing
this
process
remain
unclear.
We
employ
cellular
cryo-electron
tomography
visualize
interactions
between
ribosomes
in
Saccharomyces
cerevisiae.
use
surface
morphometrics
tools
identify
optimally
oriented
on
mitochondrial
membranes
for
protein
import.
This
allows
us
establish
first
subtomogram
average
structure
ribosome
at
native
context,
which
showed
three
distinct
connections
with
outer
membrane
surrounding
peptide
exit
tunnel.
Further,
analysis
demonstrated
that
primed
import
cluster
sites
local
constrictions
inner
membranes.
Overall,
our
study
reveals
architecture
spatial
organization
surface,
providing
context
define
mediate
efficient
co-translational
Protein
translocation
across
the
endoplasmic
reticulum
(ER)
membrane
is
an
essential
step
during
protein
entry
into
secretory
pathway.
The
conserved
Sec61
protein-conducting
channel
facilitates
polypeptide
and
coordinates
cotranslational
polypeptide-processing
events.
In
cells,
majority
of
stably
associated
with
a
heterotetrameric
complex,
translocon-associated
complex
(TRAP),
yet
mechanism
by
which
TRAP
assists
in
remains
unknown.
Here,
we
present
structure
core
Sec61/TRAP
bound
to
mammalian
ribosome
cryogenic
electron
microscopy
(cryo-EM).
Ribosome
interactions
anchor
conformation
that
renders
ER
locally
thinner
significantly
curving
its
lumenal
leaflet.
We
propose
stabilizes
exit
tunnel
assist
nascent
insertion
through
provides
ratcheting
lumen
mediated
direct
interactions.
Life Science Alliance,
Год журнала:
2024,
Номер
7(8), С. e202302496 - e202302496
Опубликована: Июнь 12, 2024
Multispanning
membrane
proteins
are
inserted
into
the
endoplasmic
reticulum
by
ribosome-bound
multipass
translocon
(MPT)
machinery.
Based
on
cryo-electron
tomography
and
extensive
subtomogram
analysis,
we
reveal
composition
arrangement
of
MPT
components
in
their
native
environment.
The
intramembrane
chaperone
complex
PAT
translocon-associated
protein
(TRAP)
associate
substoichiometrically
with
a
translation-dependent
manner.
Although
is
preferentially
part
MPTs
bound
to
translating
ribosomes,
abundance
TRAP
highest
associated
non-translating
ribosomes.
average
TRAP-containing
reveals
intermolecular
contacts
between
luminal
domains
an
unknown
subunit
back-of-Sec61
complex.
AlphaFold
modeling
suggests
this
nodal
modulator,
bridging
nicalin
TRAPα.
Collectively,
our
results
visualize
variability
factors
environment
dependent
translational
activity
ribosome.
The
protein
translocon
at
the
endoplasmic
reticulum
comprises
Sec61
translocation
channel
and
numerous
accessory
factors
that
collectively
facilitate
biogenesis
of
secretory
membrane
proteins.
Here,
we
leveraged
recent
advances
in
cryo-electron
microscopy
(cryo-EM)
structure
prediction
to
derive
insights
into
several
novel
configurations
ribosome-translocon
complex.
We
show
how
a
transmembrane
domain
(TMD)
looped
configuration
passes
through
lateral
gate
during
insertion;
nascent
chain
can
bind
constrain
conformation
ribosomal
uL22;
translocon-associated
(TRAP)
complex
adjust
its
position
different
stages
biogenesis.
Most
unexpectedly,
find
large
proportion
complexes
contains
RAMP4
intercalated
Sec61’s
gate,
widening
central
pore
contributing
hydrophilic
interior.
These
structures
lead
mechanistic
hypotheses
for
function
highlight
remarkably
plastic
machinery
whose
conformations
composition
dynamically
diverse
range
substrates.
The
protein
translocon
at
the
endoplasmic
reticulum
comprises
Sec61
translocation
channel
and
numerous
accessory
factors
that
collectively
facilitate
biogenesis
of
secretory
membrane
proteins.
Here,
we
leveraged
recent
advances
in
cryo-EM
structure
prediction
to
derive
insights
into
several
novel
configurations
ribosome-translocon
complex.
We
show
how
a
transmembrane
domain
(TMD)
looped
configuration
passes
through
lateral
gate
during
insertion;
nascent
chain
can
bind
constrain
conformation
ribosomal
uL22;
translocon-associated
(TRAP)
complex
adjust
its
position
different
stages
biogenesis.
Most
unexpectedly,
find
large
proportion
complexes
contains
RAMP4
intercalated
Sec61’s
gate,
widening
central
pore
contributing
hydrophilic
interior.
These
structures
lead
mechanistic
hypotheses
for
function
highlight
remarkably
plastic
machinery
whose
conformations
composition
dynamically
diverse
range
substrates.
