Nuclear Transport, ER Translocation, and Golgi Protein Sorting: Key Concepts and Proteins

Nuclear import signal

NLS

Nuclear export signal

NES

NLS property

necessary and sufficient

NES property

necessary and sufficient

Most common NLS

basic positively charged amino acids

Most common NES

leucine-rich motif

Protein that imports into nucleus

importin

Protein that exports from nucleus

exportin

Protein family for nuclear transport

karyopherins

Directionality of nuclear transport

Ran-GTP gradient

Ran-GTP highest location

nucleus

Ran-GDP highest location

cytoplasm

Protein that converts Ran-GDP to Ran-GTP

RCC1

Protein that converts Ran-GTP to Ran-GDP

RanGAP1

Function of Ran-GTP in import

release cargo in nucleus

Function of Ran-GTP in export

assemble export complex in nucleus

ER translocation channel

Sec61 translocon

Type of translocation into ER

co-translational

Protein that stops translation

SRP

Protein that cleaves signal sequence

signal peptidase

Signal sequence property

hydrophobic amino acids

Protein folding helpers

chaperones

Example ER chaperone

BiP

Disulfide bond enzyme

PDI

N-linked glycosylation amino acid

asparagine

N-linked consensus sequence

N-X-S/T

Lipid carrier for glycosylation

dolichol phosphate

Number of sugars in core glycan

14

Purpose of glycosylation

protein folding and stability

Protein that detects misfolding

UGGT

Misfolded protein degradation

ERAD

Stress response pathway

UPR

PERK function

inhibits protein synthesis

PERK target

eIF2α

ATF6 function

transcription factor activation

ATF6 activation location

Golgi

COPII function

ER to Golgi transport

COPI function

Golgi to ER transport

Clathrin function

vesicle formation to lysosome/endocytosis

Adaptor proteins for clathrin

AP1 and GGA

GTPase for clathrin vesicles

Arf1

Protein for vesicle scission

dynamin

Protein for vesicle docking

Rab

Protein for vesicle fusion

SNARE

v-SNARE location

vesicle membrane

t-SNARE location

target membrane

Protein for SNARE disassembly

NSF

Golgi structure order

cis medial trans

Golgi function

protein modification and sorting

Lysosome targeting signal

M6P

M6P receptor function

binds lysosomal proteins

Default pathway without M6P

secretion

Constitutive secretion

continuous release

Regulated secretion

signal-triggered release

Endocytosis definition

uptake into cell via vesicles

Early to late endosome change

increasing acidity

Late endosome pH

~5-5.5

Effect of low pH

receptor-ligand dissociation

Multivesicular body

MVB

MVB function

protein sorting for degradation

MVB budding direction

inward away from cytoplasm

MVB sorting machinery

ESCRT

Degradation signal for proteins

ubiquitin

Receptor recycling

path back to plasma membrane

Endomembrane system definition

network of organelles using vesicles

Organelles in endomembrane system

ER Golgi lysosome endosome plasma membrane

Organelles NOT in system

mitochondria chloroplast

Vesicle transport steps

budding trafficking docking fusion

Retrograde transport definition

backward movement of proteins

ER exit sites

ERES

Function of ERES

vesicle budding to Golgi

Protein without NLS entry

piggyback import

Protein shuttling definition

moves between nucleus and cytoplasm

Localization depends on

NLS vs NES strength

Resolution definition

ability to distinguish two points

Magnification definition

increase image size

Better resolution

shorter wavelength

Better resolution factor

higher numerical aperture

Light microscope resolution

~200 nm

Electron microscope resolution

~0.2 nm