Lecture 11: Secretion and Endocytosis

what do vesicles bud from

donor membrane

what do vesicles fuse with

specific target membrane

what do coat proteins bind to

membrane cargo proteins

which SNARE is Donor membrane-specific to

v-SNARES

what is the process of vesicle fusing with target membrane

vesicle uncoats in cytosol, v-SNARES bind with specific t-SNARES, fusion occurs

Three major types of transport-specific coated vesicles

COPII, COPI, Clathrin

what are coated vesicles associated with

GTPases that control assembly/disassembly of vesicle coats

Assembly/Disassembly of the COPII coat step 1

Sar1-GDP binds to ER integral membrane protein Sec12

what binds to ER integral membrane protein Sec12 in Assembly/Disassembly of the COPII coat step 1

Sar1-GDP

what does Sar1-GDP bind to in Assembly/Disassembly of the COPII coat step 1

ER integral membrane protein Sec12

what does Sec 12 contain

Guanine Exchange Factor activity

GEF

Guanine Exchange Factor

what does Guanine Exchange Factor activity do

exchanges GDP for GTP

what does Sar1-GTP do

integrates into the ER membrane cytosolic face

Assembly/Disassembly of the COPII coat step 2

Sar1-GTP recruits the COPII coat protein complex, curves and pinches off ER membrane region as COPII-coated vesicle

COPII coat protein complex

Sec23/Sec24, v-SNARES, others

what does Sar1-GTP recruiting the COPII coat protein complex result in Assembly/Disassembly of the COPII coat step 2

curves and pinches off ER membrane region as COPII-coated vesicle

Assembly/Disassembly of the COPII coat step 3 & 4

Sar1 hydrolyzes GTP, coat proteins and Sar1-GDP disassemble

what is the result when Sar1 hydrolyzes GTP, and coat proteins and Sar1-GDP disassemble in Assembly/Disassembly of the COPII coat step 3 & 4

leaves uncoated cargo vesicle and v-SNARES for target membrane fusion

what does v-SNARE/t-SNARE binding ensure

fusion to correct membrane

VAMP

v-SNARE protein

what does v-SNARE protein form

stable coil-coil interactions with matching t-SNARE proteins

t-SNARE proteins

syntaxin and SNAP-25

what happens when the correct fusion happens

SNARE proteins disassemble

what does The cytosolic region of cargo proteins possess

short targeting signal sequence motifs

what is the purpose of The cytosolic region of cargo proteins possessing short targeting signal sequence motifs

to bind to specific coat proteins

what does Sar1-GTP do in COPII Vesicle complex

recruits Sec23/Sec24 to the ER membrane

what does Sec24 do in COPII Vesicle complex

interacts with cytosolic diacidic targeting signal in cargo protein, recruits cargo to membrane vesicle

CFTR

Cystic Fibrosis

what causes Disease relevance

ΔF508 mutation in Cystic Fibrosis

what happens in Disease relevance

CFTR misfolds and prevents its recruitment to COPII vesicles for ER-Golgi transport

what is the initial transport stage of the secretory pathway

Forward transport between ER and cis-Golgi

another name for forward transport

anterograde transport

COPII vesicle-mediated protein trafficking between ER and Golgi step 1

COPII coat assembles on ER membrane to form vesicles

what are the vesicles containing when COPII coat assembles on ER membrane during anterograde transport

v-SNARE, Membrane proteins with cytoplasmic signal sequences, Soluble cargo proteins bound to membrane receptors

COPII vesicle-mediated protein trafficking between ER and Golgi step 2-3

COPII pinches off coated vesicle, disassembly exposes v-SNARE for fusion targeting at cis-Golgi membrane tSNARE

what does reverse transport between cis-Golgi and ER do

recycles components of the secretory pathway

another word for reverse transport

retrograde transport

COPII vesicle-mediated protein trafficking between ER and Golgi step 4

COPI coat assembles on cis-Golgi membrane to form vesicles

what are the vesicles containing when COPII coat assembles on ER membrane during retrograde transport

v-SNARES, missorted ER-resident proteins

COPII vesicle-mediated protein trafficking between ER and Golgi step 5

COPI coat disassembly exposes cis-Golgi v-SNARE

COPII vesicle-mediated protein trafficking between ER and Golgi step 6

cis-Golgi v-SNARE interact with ER t-SNARE to fuse vesicle with ER membrane

where must ER resident proteins remain

in ER

where may ER resident proteins be missorted to

cis-Golgi network

what happens If the KDEL sorting sequence is detected in the cis-Golgi

they will bind to cis-Golgi KDEL receptors and be incorporated into COPI vesicles

trans-Golgi network function

sorts proteins into vesicles targeted for different destinations

what do COPI vesicle do with golgi enzymes

return them backwards

how are Lysosomal enzymes delivered in the trans-Golgi network

by a clathrin-coated vesicle pathway

where does the clathrin-coated vesicle pathway deliver Lysosomal enzymes in the trans-Golgi network

lysosomes, or endosomes

which vesicles have unknown coats in the trans-Golgi network

Constitutive secretory vesicles, regulated secretory vesicles

what happens in the end of the trans-Golgi network

transport secreted proteins and plasma membrane proteins to cell surface

what are Clathrin-coated vesicles largely responsible for

endosome and lysosome-related trafficking of cargo

what do Clathrin-coated vesicles rely on

Adaptor protein complexes

AP complex

Adaptor protein complex

what do AP complexes do for Clathrin-coated vesicles to rely on them

they select cargo proteins and recruit clathrin to the transport vesicle

how do AP complexes select cargo proteins

recognize cytosolic signal sequences on cargo proteins

what happens after AP complexes recognize cytosolic signal sequences on cargo proteins

recruit clathrin

what does Dynamin with Clathrin-coated vesicles

hydrolyzes GTP to pinch off clathrincoated vesicles

LDL

low-density lipoprotein

Endocytic pathway for internalizing low-density lipoprotein step 1

Cell-surface LDL Receptor binds LDL

LDLR

LDL receptor

what does LDLR have at the cytosolic tail

NPXY sorting signal

what does the NPXY Sorting Signal at the cytosolic tail of the LDLR do

interacts with AP2

Endocytic pathway for internalizing low-density lipoprotein step 2

Clathrin-coated pit forms

what do the Clathrin-coated pit contain in Endocytic pathway for internalizing low-density lipoprotein step 2

LDL-LDLR complexes

how are Clathrin-coated pit formed in Endocytic pathway for internalizing low-density lipoprotein step 2

Pinched off as clathrin-coated vesicle by dynamin-mediated mechanism

what does the dynamin-mediated mechanism require

GTP hydrolysis

Endocytic pathway for internalizing low-density lipoprotein step 3

Vesicle fuses with endosome, acidic pH releases LDL particle from receptor

Endocytic pathway for internalizing low-density lipoprotein step 4

Late endosome fuses with lysosome, LDL particle broken downvby lysosomal enzymes

Endocytic pathway for internalizing low-density lipoprotein step 5

LDLR is recycled to the cell surface