Please enable JavaScript.
Coggle requires JavaScript to display documents.
Moving Proteins into Membrane and Organelles, Proteins - Coggle Diagram
Moving Proteins into
Membrane and Organelles
Mitochondria
and chloroplast
contains its own DNA, rRNA, tRNA, organelles and some proteins
growth and division independent from cell
proteins need specific
amphipathic N-terminal targeting sequence
because most of its proteins imported post translationally
Sequence removed by proteases in matrix
Cytosolic chaperone proteins
maintain proteins in unfolded state in cytoplasm
Only unfolded proteins can be imported into organelles
Translocation in mitochondria occurs at sites where outer
and inner membranes of organelles are close
Matrix proteins
bind to receptors on outer membrane
transfered to
Tom40
translocation through outer and inner
membrane occurs at same time
driven by ATP hydrolysis by Hsp70
and proton-motive force across inner membrane
Other than matrix
usually contain 2 or more targetting sequences
some destined for inter membrane space or inner
membrane go into matrix then get redirected
other go straight where they need to go
Peroxisome
Matrix protein
C targetting sequence (PTS1)
few have N targetting sequence PTS2
sequences not cleaved
Bind to cytosolic receptor protein
then directed to translocation machinery
ATP hydrolysis dependent
many Fold in cytosol and traverse later
Membrane proteins
different pathway and different sequence
New peroxisomes
from precursor membranes from ER
and by division of preexisting organelles
Nucleus
Nuclear Pore Complexes
30 different nucleoporins
FG nucleoporins contain
short FG repeats line the central transporter channel
Proteins over 40kDa
require assistance of nuclear transport receptor
interact with molecule and FG repeats
Nuclear localization signal (NLS)
for protein that needs to get in
Nuclear Export Signal (NES)
for protein that needs to get out
If a protein shuttles in and out, it
has both
Ran, monomeric G protein
allows unidirectional export and import
Ran GEF in nucleus (GDP --> GTP)
Ran GAP in cytoplasm (GTP --> GDP)
mRNP transport mRNA
they bind with heterodimeric mRNO exporter
in the nucleoplasm that interacts with FG repeats
RNA helices associated with cytoplasmic
filaments of Nuclear Protein Complex
removes mRNP once transport complete
to and across ER
Cytosolic ribosomes
secreted proteins
integral plasma membrane proteins
ER proteins
Golgi and lysosome proteins
Signal Sequence on N-terminus
--> hydrophobic amino acids
cotranslational translocation
SRP recognizes and binds ER
signal sequence on nascent protein
SRP binds SRP receptor on ER
SRP and receptor mediate insertion of
nascent protein in translocon
Sec61 complex
2 GTP hydrolyzed, dissociation of SRP, ribosome
continues translation
Translocon
has central channel
lined with hydrophobic residue that allows
protein passage but not ions and small molecules
Post-translational translocation
completed secretory protein targeted to ER membrane
its signal sequence interacts with translocon
Ratcheting mechanism, ATP hydrolysis + BiP, gets in
Cotranslational and post-translational
signal peptidase in ER cleaves the ER
signal sequence from secretory protein
Insertion of membrane
proteins in ER
5 topological classes
Type III
same orientation as I but no cleavable sequence
Tail-anchored
Hydrophobic segment at C that spans membrane
Type II
N cyto
C ER
Type IV
Multipass proteins
odd (diff sides) even (same sides)
Type I
N-term ER sequence cleaved
C cyto N ER
Lipid-anchor type
GPI anchored
N terminus in ER
Stop-transfer anchor sequence TYPE I
hydrophobic sequence (alpha helix)
will become transmembrane segment
Signal-anchor sequence TYPE II and III
ER signal sequence and anchor
direction of protein depends on orientation of this sequence
Protein modification
folding and quality control in ER
N-linked oligosacch
bind to asparagine
2 N-acetylglucosamine
at least 3 mannose residues
have several branches
beings with 14 residue high mannose
oligo from lipid in ER membrane
then 3 glucose and 1 mannose removed
O-linked oligosacch
Serine/threonine
short
1-4 sugar residues
Oligosaccharides
assist in folding
protect from proteolysis
cell-cell adhesion
antigens
Disulfide bonds
added to many soluble secretory proteins
exoplasmic (not cytoplasmic) domain of
membrane proteins in ER (catalyzed by PDI)
Proper Folding
BiP, calnexin, calreticulin, peptide-prolyl
isomerases ensure proper folding
Subunits of multimerix proteins assemble
in the ER
Protein folding
only properly folded go to Golgi
accumulation of abnormally folded
can increase expression of ER protein
folding catalyst
Unassembled or misfiled proteins
transporter back to cytosol for degradation
Proteins
Organelles
(needs a targeting sequence)
Usually on N terminal
Needs a translocation channel
Mitochondria
Chloroplast
ER
Peroxisome (can fold before)
Nucleus
Extracellular
Cytosol