Transcript Vesicle Formation at the Plasma Membrane and Trans

Vesicle Formation at the Plasma
Membrane and Trans-Golgi
Network: The Same but Different
M. A. McNiven, et al., Science 313, 1591 (2006)
Department of Biochemistry and Molecular Biology and
the Miles and Shirley Fiterman Center for Digestive
Diseases, Mayo Clinic College of Medicine, Rochester
Liangfang Zhao, Yanqing Lin & Zhiling Yao
Life Science College, CNU
2007.10.30
Abbreviations
• PM: Plasma Membrane
• TGN: Trans-Golgi Network
• CCV: Clathrin-Coated Vesicle
• APs: Adaptor Proteins
• EGF: Epidermal Growth Receptor
• GGAs: Golgi-localized, γ-earcontaining,
Adenosine diphosphate Ribosylation Factor
(ARF)
• PIP2: PhosphatidylInositol 4,5-bisPhosphate
• PI4P: PhosphatidylInositol 4-monoPhosphate
• UIMs: Ubiquitin Interacting Motifs
Overview: yin & yang relationship
• Sorting, packaging, vesiculation, transport
of membrane and protein cargo
active exchange of membranes & protein
cargo;
highly conserved mechanisms in vesicle
formation & scission
• In and out of the cell
• Membrane continuum
Index
• I. similarities and variations in sorting
mechanisms
• II. Lipid-membrane binding, bending and
pinching
• III. Vesicle scission
I. similarities and variations in
sorting mechanisms
• Similarities in protein-sorting
mechanisms at the PM and TGN
• Variations of a common sorting
machine
1.Similarities in protein-sorting
mechanisms at the PM and TGN
• Key functions: selective sequestration
and packaging of protein cargo
• Central scaffold: clathrin and its
associated coat proteins
APs and monomeric clathrin-associated
sorting proteins
• “first line” of cargo-sequestration specificity
• AP1-4
similar organization, subunits, structure;
different cellular localization patterns,
vesicle-formation processes
AP: mediate protein sorting
• Recognition of sorting motifs of the cytosolic
domains of transmembrane proteins
• Three classes
Asn-Pro-X-Tyr: AP-2 at the PM while interact
with non-AP-2
Tyr-X-X-Φ: μsubunit of all 4 APs
[Asp-Glu] X-X-X-Leu [Leu-Ile]: AP1-3 yet
different preferences
Conclusion for PART 1
Different affinities
between leaving and
being internalized
2.Variations of a common sorting
machine
• Several layers of regulation and targeting:
provide specificity
• Different lipids & phosphoinositides; small
GTPases; GGAs
Lipids
• Cholesterol, sphingoipids, phosphoinositides
• Rafts (lipid microdomains)
mediate clathrin-independent vesicle
formation
participate in sorting at the TGN
ratio differ: maintain the participation of
membrane microdomains
• Form vesicle: inositol phospholipids
different combinations of
phospho-modifications: PIP2 &
PI4P(LESS TIDY)
Same phosphoinositide:
essential in multiple
distinct vesicle formation
processes at both sides
Small GTPases
• Regulate secretory & endocytic vesicle
formation
• TGN targeting of AP-1: Active ARF1 &
Golgi-enriched PI4P
• PM CCV formation: ARF family
dependent in some cases
GGAs: function along with the APbased sorting system
• Recruitment to Golgi: ARF dependent
• Generate CCVs’ subset which targets to
lysosomes: function along with AP-1
• Mediate sorting of lysosome-targeted
proteins: bind to different dileucine motifs
AP-1: [DE]XXXL[LI]
GGAs: Asp-X-X-Leu-Leu
Ubiquitin modification
• TGN: Initiate nascent proteins sorting
• PM: Sort endocytosed proteins to endosomes &
lysosomes
• At both vesicle-formation sites:
PM: Eps15 & Epsin----sequester & sort activated
EGF receptors
bind each other & AP-2
contain UIMs
TGN: GGAs & Eps15
Eps15: AP-1
costain