Biol 305- Vesicle Trafficking (E3)

i'm just so excited to get to ligands those little guys are my favorite

vesicle definition:

small, spherical membrane bound structures found within and outside of cells

basic steps of vesicle formation, translocation, and docking:

1. Initiation of vesicle at a specific location in a donor membrane

2. Recruitment of cargo proteins to the vesicle

3. Vesicle release from donor membrane/ Scission

4. Protein coat is disassembled and released

5. Vesicle is transported to target membrane

6. Specific recognition of the target membrane by the vesicle to initiate docking

7. Fusion of target membrane with vesicle

pathways which use vesicle transport:

1. secretory pathway

2. endocytosis

movement in the secretory pathway which is “forward”, or from ER to Golgi:

anterograde

movement in the secretory pathway which is “reverse”, or from Golgi back to the ER:

retrograde

how are vesicles grouped?

according to their coat proteins

3 types of vesicles:

1. COP2

2. COP1

3. Clathrin

COP2 movement:

anterograde

COP2 GTPase:

Sar1

COP1 movement:

retrograde

COP1 GTPase:

ARF

Clathrin movement:

lysosome to trans Golgi

Clathrin GTPase:

ARF

coat assembly begins with ______ recruitment to the membrane in COP2:

Sar-1

What protein facilitates the insertion of Sar-1 into the membrane?

Sec12, compels a hydrophobic tail on Sar-1 to insert into the ER membrane

Sec 23 and 24 proteins interact with ________ proteins to induce ________

integral membrane/ deformation

___________ is responsible for vesicle release and coat disassembly

GTP hydrolysis of Sar-1, the hydrophobic tail removes from the membrane and Sar-1 leaves, taking coat proteins with it

sequence signals which can select cargo proteins in the vesicle:

1. luminal sequences

2. cytoplasmic sequences

how do luminal signaling sequences select cargo proteins?

they recruit soluble proteins and bind them to intermembrane receptors

how do cytoplasmic signaling sequences select cargo proteins?

they are found in intermembrane proteins and will bind to the coat proteins

composition of a clathrin coat:

adapter protein/ AP complex

clathrin protein

components of a clathrin triskelion:

3 large subunits/ heavy chains

3 small subunits/ light chains

there are ____ triskelions in a clathrin coat:

36

clathrin coated molecules use ______- to pinch off from the donor membrane:

dynamin which is GTP hydrolysed

proteins which help regulate vesicle docking recognition:

1. Rab proteins

2. SNARE proteins

function of Rab proteins:

associate with the cytosolic face of the vesicle and is bound to GTP

will bind to Rab effector proteins on target membrane

once GTP is hydrolyzed Rab dissociates and fusion occurs

isoprene function in Rab:

connects Rab to the vesicle membrane

SNARE protein function:

associate with the vesicle membrane and target membrane to bring the two close for fusion

types of SNARE proteins:

V SNARE

T SNARE

function of V SNARE:

associates with the vesicle and is a single polypeptide

function of T SNARE:

associated with the target membrane and are multi-protein complexes

how do SNARE’s work?

V and T SNARE’s will interact and form 3 alpha helices, which bring the vesicle and target membrane together despite the energetic unfavorable-ness

what happens to SNARE’s once the two membranes fuse:

they become a part of the target membrane and must be untangled and sent back to their respective organelles (V SNARE) before they may be reused

COP1 coats recruit cargo proteins with ________ that will bind to ________

KDEL sequences/ KDEL receptor proteins

KDEL receptors are recruited by ________

KKXX cytoplasmic signal sequence

where is the KDEL receptor recruitment sequence bound?

COP1 alpha and beta subunits

clathrin coated proteins recruit cargo proteins with ______ which bind ________

mannose-6-phosphate tails/ M6P receptors

M6P receptors will ______ at low pH in the endosome

dissociate

why does receptor mediated endocytosis occur?

sometimes, the clathrin coated vesicle is accidentally sent outside the cell instead of to the trans Golgi, so the M6P tailed proteins must be brought back into the cell