vesicular transport

protein transport between ER, golgi, plasma membrane and vesicles is achieved through

vesicular transport

how does vesicular transport work?

the vesicles travel between compartments in the cell along defined, regulated pathway and fuse specifically with their targetsto deliver their cargo.

3 protein coat complexes

clathrin, COPI, COPII

vesicular sorting depends on the assembly of a special — — formed at specific locations along a given donor compartment

protein coat

COPI

coats vesicles moving from golgi to ER, golgi to plasma membrane (secretory vesicles) and within the golgi

COPII

coats ER to golgi vesicles

clathrin

cell surface to the interior, traffics from golgi to endosomal compartments

the curvature of the membrane is based on the

the assembly of coat proteins

in order for fusion to happen, coat proteins must

disassemble

how do coat proteins recognze different membranes

• via the membrane protein signals

• info in the membrane themselves

phospholipids containing inositol head groups

mark organelles and membrane domains

inositol can get phosphorylated at various locations by different

lipid kinases— This phosphorylation can create distinct signaling molecules that play roles in cellular processes.

PI’s can recruit various proteins that possess

lipid binding domains

lipid binding domains

usually only recognize a specific type of PI (different types of phosphorylated positions)

how many different possible phosphorylated positions?

7

— — bind to membrane proteins and recruit coat proteins

adapter proteins

cargo receptors

bind to soluble proteins in organelles that recruit them into vesicles, in their cytoplasmic tails they recruit the adPTOR proteins which can then bind the coat proteins

what regulates vesicular transport

GTPases

GTPases control what processes in cell

Sar-1 (GTPase) function

regulates COPII assembly

Arf proteins (GTPases) function

regulates COPI and clathrin assembly

transport vesicles must be — — in recognizing the correct target membrane with which to fuse

highly selective

two classes of proteins involves in making sure vesicles trafficking and fusion of membrane occurs in highly selective manner

SNAREs and Rabs

target membranes display — receptors that recognize the appropriate markers

complementary

what type of protein is Rabs

GTPase, works together with other proteins to regulate the initial docking and tethering of the vesicle to the target membrane, they catch vesicles

SNARE proteins

catch vesicles (essentially spring loaded proteins) provide specificity, catalyze vesicular fusion with target membrane

v-SNAREs

on the vesicle

t-SNAREs

on the target membrane

both types of snares consist of

long alpha helices, form coiled coil — the force of this interaction drives the fusion of the membrane

To pull snares apart after fusion process finished

needs ATP

energy is needed to

pry apart v and t snares to their original states

Rabs (GTPase)

Tethering ng is — dependent, fusion is — dependent

GTP, ATP

any protein that has to go into a membrane enclosed organell that isnt nucleus, mitochondrion, chloroplast must pass through —

ER

membrane proteins have — — in their cytosolic tails that are recognized by coat proteins

exit signals

soluble proteins bind to cargo receptors that have exit signals in ther cytosolic tails

transport vesicles leaving the ER fuse together to form intermediate compartments called

vesicular tubular clusters

vesicular tubular clusters

travel towards golgi via motor proteins on microtubule tracks, generate coated vesicles going back to the ER (retrograde transport)

ER retrieval signals

membrane ER resident proteins, soluble Er resident proteins

membrane ER resident proteins

retrieval signals in their cytosolic tails, recognized by COPI coat proteins

soluble ER resident proteins

retrieval signals within their structure bind to receptors, ex. KDEL sequences

KDEL

brings things back to ER, interact with COPI proteins

two current models for how cargo travels through golgi

cisternae: static and dynamic

static cisternae — vesicular transport model

• golgi doesn’t change

• vesicles travel between them

• vesicles can move forward and backward

dynamic cisternae — cisternal maturation model

• move upward, changing their properties slightly as they migrate

• as new membrane comes in it becomes the cis phase, the previous cis phase becomes a medial phase, and the trans phase gets pushed off

two pathways to transport from the trans golgi to the cell exterior

constitutive secretory pathway and regulated secretory pathway

constitutive secretory pathway

• vesicles bud off from golgi, get to membrane recognized by RABS, snares snap in place, which fuses to the membrane and allows secretion

• once in right place, it will fuse and secrete

regulated secretory pathway

• only secreted on demand/when needed

• they are concentrated in secretory vesicles but cannot be transported unless there is outside signal

• Ca used for this most of the time

clathrin-coated vesicles

• used for transport between plasma membrane, endosomal system, and golgi

• 1st coat protein

• composed of 3 copies each of heavy chain and light chain

• arranged in a “triskelion”

clathrin

the pinching off of clathrin coated vesicles is controlled in part by the cytoplasmic protein —

dynamin

dynamin

• GTP and lipid binding

how to target materials to get to lysosomes

• carry a unique marker: mannose 6 phosphate (M6P) groups which is added to N linked oligosaccharides in cis-golgi

• this is then recognized by M6P reeptor in TGN and packaged into clathrin-coated vesicles for delivery to lysosomes

endosomes

• intermediate organelles in vesicular transport pathways

• vary in size/shape

• receive cargo from golgi and PM

• not permanent

three classes of endosomes

early, late, recycling

early endosomes

as a result of endocytosis

recycling endosomes

brings materials back up to plasma membrane

how do early endosomes mature

by becoming increasingly acidic and hydrolitic

multivesicular bodies

when late endosomes end up creating vesicles into itself

phagocytosis, what are the vesicles called?

cell eating, ingestion of large particles (ex. microorganisms/dead cells); phagosomes

pinocytosis — what are the vesicles called

cellular drinking, pinocytic vesicles; includes receptor mediated endocytosis

cholesterol gets into cells via

receptor mediated endocytosis

transcytosis

molecules internalized at one end of a ‘polarized’ cell are transported to a different end