LECTURE 2: VESICULAR TRAFFICKING THROUGH THE ENDOMEMBRANE
SYSTEM
PROTEIN TRAFFICKING
• Proteins travel as cargo with vesicles from the Golgi complex to the cell
membrane.
• Proteins travel as cargo with vesicles from ER to Golgi complex.
• ER resident proteins stay in ER
• Some proteins leave:
o Golgi complex
o Lysosome
o Cell membrane
o Secreted out of cell
• Transported in vesicles through Golgi complex
GOLGI COMPLEX
o Series of elongated, flat sacs (cisternae)
• Vesicles
o transport proteins from ER to Golgi cis-cisternae
o transport proteins away from Golgi trans-cisternae
• exocytosis: vesicles fuse with cell membrane to release protein from cell
• constitutive secretory pathway
o proteins released immediately after synthesis + transport
o secretory vesicles go from trans-Golgi to cell membrane
• regulated secretory pathway
o proteins kept in cell until signalled release
o Secretory granules: secretory vesicles held in cell
• Other proteins carried away from Golgi-trans to form lysosome
• Fuse with vesicles formed at cell membrane (endosomes)
• Capture + transport macromolecules from outside cell
• Wheat germ agglutinin
o Used to recognize Golgi complex with fluorescence
o Lectin that recognizes N-linked polysaccharides in Golgi cisternae
GOLGI CISTERNAE
• Golgi complex: region containing a series of
elongated vesicle sacs (cisternae)
• Cis-Golgi: collection of coalescing vesicles
emanating from ER to form cis-cisternae
• Medial cisternae: in middle of complex
• Trans-cisternae: furthest from ER
o Break out into vesicles to form trans-Golgi
• Many mobile spherical vesicles associated through complex
• Dynamic
1. vesicles fuse to form new cisternae
, 2. cisternae change shape + move throughout complex
3. vesicles form from membranes of cisternae
• Cisternae contain resident proteins needed for post-translational modification (PTM) of
transported proteins
• Anterograde transport through Golgi complex
o Proteins from ER to cell membrane through Golgi
o Moving in “normal/forward” direction
o Move from cis- to medial to trans- Golgi
MODELS OF ANTEROGRADE TRANSPORT
• Model A:
o Vesicles carrying protein cargo move from cis to medial and from medial
to trans
• Model B:
o Proteins stay in cisternae
o Cisternae move forward through Golgi complex
o Needs vesicles moving backwards (retrograde)
CISTERNAL MATURATION - MODEL (B)
• Label different types of proteins + follow their movement
• Immuno-TEM images to visualize protein specific antibody to one of two
proteins
• (c) antibody to cell membrane protein
o Expected to move in anterograde direction
o Found only in cisternal sacs, not in any associated vesicles
§ Proves that vesicles are not required for anterograde
movement
• (d) antibody to medial Golgi protein
o Expected to move to the position of a trans-Golgi cisterna
o Moved anterograde
o Medial Golgi protein are mis-localized
o Requires resorting of proteins in retrograde vesicles
o Antibodies in medial Golgi cisternae AND in vesicles
§ Proves that cisternae move forwards through the complex
SUMMARY
• Cisternal sacs + cargo move anterograde through
Golgi complex (towards top)
• Cisternae are defined based on location within
complex:
o Cis-Golgi become medial-Golgi
o Medial-Golgi become trans-Golgi
• Golgi cisternae containing cargo move in anterograde
direction
• Implications:
SYSTEM
PROTEIN TRAFFICKING
• Proteins travel as cargo with vesicles from the Golgi complex to the cell
membrane.
• Proteins travel as cargo with vesicles from ER to Golgi complex.
• ER resident proteins stay in ER
• Some proteins leave:
o Golgi complex
o Lysosome
o Cell membrane
o Secreted out of cell
• Transported in vesicles through Golgi complex
GOLGI COMPLEX
o Series of elongated, flat sacs (cisternae)
• Vesicles
o transport proteins from ER to Golgi cis-cisternae
o transport proteins away from Golgi trans-cisternae
• exocytosis: vesicles fuse with cell membrane to release protein from cell
• constitutive secretory pathway
o proteins released immediately after synthesis + transport
o secretory vesicles go from trans-Golgi to cell membrane
• regulated secretory pathway
o proteins kept in cell until signalled release
o Secretory granules: secretory vesicles held in cell
• Other proteins carried away from Golgi-trans to form lysosome
• Fuse with vesicles formed at cell membrane (endosomes)
• Capture + transport macromolecules from outside cell
• Wheat germ agglutinin
o Used to recognize Golgi complex with fluorescence
o Lectin that recognizes N-linked polysaccharides in Golgi cisternae
GOLGI CISTERNAE
• Golgi complex: region containing a series of
elongated vesicle sacs (cisternae)
• Cis-Golgi: collection of coalescing vesicles
emanating from ER to form cis-cisternae
• Medial cisternae: in middle of complex
• Trans-cisternae: furthest from ER
o Break out into vesicles to form trans-Golgi
• Many mobile spherical vesicles associated through complex
• Dynamic
1. vesicles fuse to form new cisternae
, 2. cisternae change shape + move throughout complex
3. vesicles form from membranes of cisternae
• Cisternae contain resident proteins needed for post-translational modification (PTM) of
transported proteins
• Anterograde transport through Golgi complex
o Proteins from ER to cell membrane through Golgi
o Moving in “normal/forward” direction
o Move from cis- to medial to trans- Golgi
MODELS OF ANTEROGRADE TRANSPORT
• Model A:
o Vesicles carrying protein cargo move from cis to medial and from medial
to trans
• Model B:
o Proteins stay in cisternae
o Cisternae move forward through Golgi complex
o Needs vesicles moving backwards (retrograde)
CISTERNAL MATURATION - MODEL (B)
• Label different types of proteins + follow their movement
• Immuno-TEM images to visualize protein specific antibody to one of two
proteins
• (c) antibody to cell membrane protein
o Expected to move in anterograde direction
o Found only in cisternal sacs, not in any associated vesicles
§ Proves that vesicles are not required for anterograde
movement
• (d) antibody to medial Golgi protein
o Expected to move to the position of a trans-Golgi cisterna
o Moved anterograde
o Medial Golgi protein are mis-localized
o Requires resorting of proteins in retrograde vesicles
o Antibodies in medial Golgi cisternae AND in vesicles
§ Proves that cisternae move forwards through the complex
SUMMARY
• Cisternal sacs + cargo move anterograde through
Golgi complex (towards top)
• Cisternae are defined based on location within
complex:
o Cis-Golgi become medial-Golgi
o Medial-Golgi become trans-Golgi
• Golgi cisternae containing cargo move in anterograde
direction
• Implications:
