BSCI330 - L15 Intracellular Transport

proteins are synthesized in

cytosol

transport relies on specific blank which are within the blank

signal sequences within the protein primary sequence

gated transport is through

the nuclear pore complex

what is gated transport used for

move proteins in and out of nucleus

how are proteins transported into the mitochondria?

transmembrane transport

what complexes involved in transmembrane transport?

TOM and TIM complexes

how are proteins imported into the ER

cotranslational tranport

cytoplasm is

cytosol and organelles

cytosol is home to

protein synthesis/degradation

metabolism

movement of proteins btwn organelles depends on

topological similarities

what does topological similarities mean

similar membrane orientations, can you interconvert w/o ripping it

movement of proteins between organelles mediated by

sorting signals and receptors

signals where

encoded on protein

receptors where

on target/place

examples of signal sequences

N-terminal, C-terminal, signal patch (3D structure)

signals are recognized

protein sorting receptors

protein sorting receptors do what

help w/ delivery of cargo to destination

3 mechanisms of moving proteins btwn cellular compartments

gated transport, transmembrane transport, vesicular transport

gated transport is protein traffic btwn

cytosol and nucleus

nuclear pore complexes function as

selective gates that actively transport specific molecules and macromolecular assemblies

can small molecules freely diffuse through nuclear pore complex?

yes

gated transport directions?

both directions

transmembrane transport is usually

irreversible unless a lot of effort is put in

what restricts the passage of large macromolecules in NPC?

nucleoporins lining the central pore

are the nucleoporins structured?

no, just loops

upon receiving a signal, channel can

open to much bigger

how is nuclear import initiated

nuclear localization signals within cargo must be recognized

what are nuclear localization signals recognized by

nuclear import receptors

import receptors are encoded by

a family of related genes

specific nuclear localization signal sequence is

5 basic amino acids in a row

nuclear transport increases blank in the cell

order

nuclear transport and energy

consumes energy

energy provided for nuclear transport is provided by

hydrolysis of GTP by small GTPase, Ran

Ran is found in

cytosol and nucleus

Ran required for

nuclear import and export systems

GTP binding blank across nuclear membrane

gradient

RAN-GEF is a

nuclear protein

RAN-GEF catalyzes

binding of GTP to RAN inside the nucleus

RAN-GEF stands for

ran guanine exchange factor

RAN-GAP is a

cytosolic protein

what does RAN-GAP do?

activates hydrolysis of GTP that is attached to RAN

what does the RAN-GAP (cytosol) and RAN-GEF (nucleus) create?

gradient of RAN-GTP across nuclear pore, more RANGTP inside nucleus than outside

nuclear import mechanism

receptor protein binding state?

can only bind to either Ran-GTP or the cargo

nuclear import mechanism:

what happens in the nucleus?

Ran-GTP binds to receptor protein, causing it to release the cargo in the nucleus

nuclear import mechanism:

what happens after Ran-GTP binds to receptor protein?

receptor protein releases cargo in nucleus

nuclear import mechanism:

what happens in the cytosol?

GTP quickly gets hydrolyzed to GDP by Ran-GAP

nuclear import mechanism:

Ran movement?

can freely move across nuclear pores to maintain gradient, so goes back into nucleus where a lot of Ran-GEFs catalyze the exchange

nuclear export mechanism:

receptor protein structure?

has to be bound to both Ran-GTP and cargo

nuclear export mechanism:

how does the nuclear export receptor end up in nucleus?

separately comes back across nuclear pore

nuclear export mechanism:

what does it bind to and where

binds Ran-GTP in nucleus, releases Ran-GDP in cytosol

can Ran-GDP bind to any cargo receptors and why

no bc it is inactive

things bound to Ran-GTP are

active and interact w/ their target

Ran-GAPS are where

in cytosol

Ran-GEFs are where

in nucleus

Ran GTP binding purpose in nuclear import?

for the receptor protein to release the cargo

Ran GTP binding purpose in nuclear export?

make the receptor protein be able to bind to cargo to take it out of nucleus

nuclear transport as means of gene regulation

some regulatory protein activity is controlled by whether they are in the nucleus or not, so when they are needed, a signal is their for their import

localization & export signals can be turned on and off by

phosphorylation or other modifications of adjacent amino acids

NFAT & Nuclear transport: T cell is activated via

antigen binding

NFAT & Nuclear transport: when Ca2+ channel opens,

Ca2+ levels increase

NFAT & Nuclear transport: rise in Ca2+ levels does what

activates calcineurin

what is calcineurin

protein phosphotase

NFAT & Nuclear transport: what does calcineurin do, and what does it cause

dephosphorylates NFAT, conformational change that exposes nuclear import sequence on protein's surface

NFAT & Nuclear transport: what does NFAT do after its import sequence gets exposed and what does it do

enters nucleus and triggers gene expression appropriate to T-cells role in immune response

the transport of proteins into mitochondria and chloroplasts had to evolve for

endosymbiosis to work

mitochondria and chloroplasts rely on

import of their proteins from the cytosol following synthesis

mitochondrial proteins are first fully synthesized as a precursor in

the cytosol, then translocated into mitochondria

signal for mitochondrial proteins

ampithatic alpha helix that folds into a conformation where certain amino acids are facing the same way

what does the ampithatic alpha helix look like

charged residues cluster on one side and uncharged residues cluster on the other side

where is the signal sequence located for mitochondrial transport

at the N terminus

TOM complex is across

the outer membrane

TIM complexes

23 and 22 function across inner membrane

TOM stands for

translocase of the outer membrane

TOM structure

receptors associated w/ translocation channel

TIM23 Complex

inner membrane protein translocater, also associated with outer mitochondrial membrane

TIM22 Complex

mitochondrial inner membrane protein translocator

TOM complex helps insert

transmembrane proteins into outer mitochondrial membrane

beta barrel structure

Cylindrical arrangement of beta sheets

transmembrane proteins with beta barrel structure are

transferred to the SAM complex for proper folding

TIM23 spans

both membranes

TIM complex transports

soluble proteins into mitochondrial matrix, membrane proteins into inner mitochondrial membrane

Hsp70 is what kind of protein

chaperonin

what pulls proteins through TIM23 channel

import ATPase complex

two reasons for ATPase activity

help unfold proteins to get them to properly folded state, for protein to be pulled through TIM complex

what happens to signal polypeptide after the protein gets put into the mitochondrial matrix

cleaved off

ATP hydrolysis helps protein

unfold

what provides energy to transport across outer mitochondrial membrane

H+ gradient

newly synthesized mitochondrial proteins in cytosol are surrounded by blank to prevent them from blank

protein-folding chaperones that prevent them from aggregating

most common protein chaperone

Hsp70

mitochondrial versions of chaperones also

exist to help them fold once they get threaded through

directional transport is (energetically)

Not energetically favorable