Chapter 13

• Intracellular Vesicular Traffic

張學偉 助理教授

The molecular mechanisms of membrane transport and the

maintenance of compartmental diversity

GFP-FUSION PROTEINS HAVE REVOLUTIONIZED THE STUDY OF INTRACELLULAR TRANSPORT

There are various types of coated vesicles

Each type is used for different transport steps in the cell.

Mediate transportfrom Golgi & fromplasma membrane

Mediate transportfrom ER & Golgi

The assembly of a clathrin coat drives vesicle formation

Major coat protein: clathrin & adaptin

There are at least four types of adaptins, each specific for a different set of cargo receptor.

by charperone (hsp70)

Both the pinching-off and uncoating of coated vesicles are

regulated processes

Not all transport vesicles are spherical

Various size & shape

Monomeric GTPase control coat assembly

SNARE proteins and targeting GTPases guide membrane transport

Trans-SNARE complex

Interacting SNAREs need to be pried apart before they can function again

cytosol

Cycle

Rab proteins (monomeric GTPase) help ensure the specificity of vesicle docking

Rab facilitate docking of transport vescicles.

cycleRab &its effectorStructure vary greatly

Function common(1.concentrate & tethervesicle near target site2. Trigger release of SNARP control protein)

SNARE may mediate membrane fusion

Process for SNARE concentrate in membrane fusion

Viral fusion proteins and SNAREs may use similar strategies

Transport from the ER through the golgi apparatus

Cargo Recruitment

ER exit site

50nm vesicle > 200 mem protein

Only proteins that are properly folded and assembled can leave the ER

ER resident protein

Incomplete

CF (Cystic fibrosis)

Defect in Cl- transport

This is not because the mutation inactivated the protein, But because the active protein is discarded before it reaches the plasma membrane.

Transport from the ER to the Golgi apparatus is mediated by vesicular tubular clusters.

Heterotypic fusion

Homotypic memb fusion is not restricted to form VTC.

The structure formed when ER-derived vesicles fuse with one another are called.

ER retrival signal

The retrieval pathway to the ER uses sorting signals

Lys-Asp-Glu-Leu (KDEL)

KKXX at c-terminal end direct interact with COPI coat

Short retrieval signal at c-terminal

Resident ER membrane protein

Many proteins are selectively retained in the compartments in

which they function

Aggregation of proteins that function in the same compartment- called kin recognition

The golgi apparatus consists of an ordered series of compartments.

Two major classes of N-linked oligosaccharide

complex

High mannoseNo new sugar added in Golgi

Oligosaccharide processing in ER and Golgi

High specificendoglycosidase

Can distinguish betweenthese two type

Proteoglycans are assembled in the Golgi Apparatus

O-linked glycosylation

Proteoglycans are secreted or anchored to plasma membrane

What is the purpose of N-glycosylation?

1. N-linked is prevalent in all eukaryotes, but absent in procaryotes.2. limited flexibility.3. Recognition4. Regulation of development5. Protective coat unit6. Cell-cell adhesion

N-linked

The golgi cisternae are organized as a series of processing compartments

Functional compartmentalization

Matrix proteins form a dynamic scaffold that helps organize the

apparatus

Transport from trans golgi network to lysosomes

Lysosome are the principal sitesof intracellular digestion

Lysosomes are heterogeneous(morphology)

The diversity reflects the wide range of digestive function.

Plant and fungal vacuoles are remarkably verstile lysosomes

Controlling size

Vacuole function:Storage, degrade, cell size, turgr pressure, homostatic device

Three pathways to degradation in lysosomes.

M6P receptor recognizes lysosomal proteins in the Trans Golgi network (TGN)

The M6P receptor shuttles between specific membranes

Transport into the cell from the plasma membrane:

endocytosis

Transport from the trans golgi network to the cell exterior:

exocytosis

Chapter 13 practice

1. The endocytic and biosynthetic-secretory and retrieval pathway.2. Utilization of different coats in vesicular traffic.3. The role of SNAREs and SNAREs-interacting proteins in vesicle

transport .4. The traffic role of COPI &COPII coat shuttling between Golgi and ER. 5. What is KDEL signal and its role in retrieval pathway.6. How to distinguish between the high-mannose oligosaccharide and

complex oligosaccharide.7. Write the full name for Glc NAc, NANA(sialic acid).8. The functional compartmentization of Golgi apparatus.9. Three pathways to degradation in lysosomes.10. How to transport lysosomal enzyme to lysosome from ER.11. Possible fates for endocytosed transmembrane receptor proteins. 12. The receptor-mediated endocytosis of LDL.13. Three best-understanding pathways of protein sorting in trans Golgi.