Vesicular Trafficking: Lysosomes;

1
Lecture 11

• Vesicular Trafficking Lysosomes
• endocytosis and exocytosis

2
(No Transcript)
3
pH is one of the mechanisms for protecting
contents in the cytosol
All major classes of macromolecules are
degraded in lysosomes
40 hydrolytic enzymes
Lysosomal glycoproteins are unusually highly
glycosylated
Vacuolar H ATPase Lysosomes Endosomes Selected
compartments of Golgi Apparatus Transport
vesicles Secreted vesicles
4
Lysosomes are highly heterogeneous Shape and
size But all have acid hydrolases The
stomach of a cell
Stained for acid phosphatase Phosphatase
substrate
5
Huge vacuoles of plant cells
Related to lysosomes Storage organelle Degradati
ve compartments Turgor pressure Homeostatic
device
Rubber Opium Garlic Proteins Pigments Noxious
molecules
6
Three pathways to degradation in lysosomes
pH 6.0
pH 5.0
7
The structure of mannose 6-phosphate on a
lysosomal enzyme
A unique marker for lysosomal proteins
8
The transport of newly synthesized lysosomal
hydrolases to lysosomes
M6P receptor
pH6.0
pH6.5-6.7
Recycling of M6P
9
A signal patch in the hydrolase polypeptide chain
provides the cue for M6P addition
Defects in the GlcNac phosphotransferase cause
a lysosomal storage disease in humans,
inclusion-cell Disease (I-cell disease)
N-acetylglucosamine
Lysosomal storage diseases
Some lysosomes may undergo exocytosis
10
(No Transcript)
11
Phagocytosis by a macrophate
Phagocytosis by a neutrophil
pseudopods
Pinocytosis cell drinking Phagocytosis cell
eating
12
The formation of clathrin-coated vesicles from
the plasma membrane
13
Caveolae in the plasma membrane of fibroblast
Lipid rafts
caveolin
14
A low-density lipoprotein (LDL) particle
Receptor-mediated Endocytosis Example
cholesterol uptake
3,000 Kd
1500 cholesterol Molecules 800 phospholipid 500
unesterified cholesterol
Atherosclerotic plaques When uptake is blocked
Atherosclerosis
Cholesterol esters Are hydrolyzed to Free
choleterol in lysosomes
500 Kd
15
Normal and mutant LDL receptor
Common endocytic signal YXXY (binding to
adaptin) But LDL receptor Asn-Pro-Val-Tyr
Coronary artery disease
16
Possible fates for transmembrane receptor proteins
Different Rabs associate with early and
late endosomes
Recycling LDL receptor
17
Receptor-mediated endocytosis of LDL
18
Sorting of transferrin (red) and opioid receptors
(green) in the recycling endosomes
Transferrin receptor recycles with its ligand
Different Rabs
Opioid receptors and EGF receptors Are not
recycled but degraded in Lysosomes along with
ligand receptor Down-regulations
19
Some early endosomes Migrate slowly along
MT Toward the cell interior And pinch off
Vesicles to form MVBs
MVBs may fuse with a late endosomal compartment
or they fuse with each other to become late
endosome
20
Lysosomes form when vesicles from trans Golgi
network fuse with late endosomes
21
Receptors and their ligands are fully accessible
to digestive enzymes in MVBs
Ubiquitin tagging facilitate the uptake of
receptors into endocytic vesicles and and
sorting into the internal membrane vesicles of
MVBs
22
Transcytosis transferring macromolecules across
ephithelial cell sheets
A newborn rat obtains antibodies from its
mothers milk
Remember transcelluar transport of glucose?
Early endosome to recycling endosome
Receptors have sorting signals
23
Exit of membrane proteins from the recycling
endosomes can be regulated
24
Two early endosomal compartments and one common
late endosomal compartment in epethilial cells
25
Exocytosis fusion of vesicles with the plasma
membrane
26
Two mechanisms of secretion
27
Three pathways of protein sorting in the trans
Golgi network
28
Secretory proteins form selective aggregates
Secretory proteins become highly
concentrated aggregation and membrane retrieval
29
Proteins are often proteolytically processed
during the formation of secretory vesicles
A prohormone
In different cells
Size of the final products Activity
30
Regulated exocytosis can be a localized response
of the plamsa membrane and its underlying
cytoplasm
Mast cell secreting histamine all over the cell
surface when on a solution of soluble stimulant
Localized exocytosis when stimulant is presented
from a solid bead
31
Two types of polarized cells
Polarized cells direct proteins from the trans
Golgi network to the appropriate domain of the
plasma membrane
32
Two ways of sorting plasma membrane proteins
Gut epithelial cells
Live cells
33
Lipid rafts in the trans Golgi network
Glycosphingolipids and cholesterol form rafts in
the lipid bilayer
May mediate sorting of glycosphingolipids and
GPI-anchored proteins To the apical plasma
membrane
34
The formation of synaptic vesicles
50 nm
35

• Summary
• Lysosomes are where most of the intracellular
  degradation
• occurs. Formation of lysosomes, sorting into
  lysosomes
• Phagocytosis, pinocytosis, receptor-mediated
  endocytosis,
• early endosomes, late endosomes, recycling
  endosomes
• Two types of exocytosis, sorting during
  exocytosis, synaptic
• vesicles.