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Transcript
• Cell Polarity and
• the Actin
• Cytoskeleton
Chapter 16 in Alberts
Cell Polarity Defines Cell Shape and Behavior
How do cells assume a particular shape?
How do cells change their shape?
Cell Polarity is Connected to the Cell Cycle
G1
Polarity Establishment
Mitotic
Exit
S
M
Rhodamine Falloidin
G2
Polarized Secretion
Rhodamine falloidin staining of yeast cells to show actin
Actin patches and Cables
Figure 16-18. Molecular Biology of the Cell, 4th Edition
The Cytoskeleton is a cytoplasmic
structure
Of polymerized protein filaments
Actin
Actin filaments = microfilaments
2 stranded helical polymers, they’re flexible
Actin subunits polymerize into filaments
Actin Polymerization is stimulated once nucleation occurs
Salt induces Polymerization
In vitro
Actin is and ATP binding protein
Actin binds to Other Proteins That Influence its Function
CHI- complex haploinsufficiency and actin
haploinsufficiency has been gaining in
appreciation as an important influence on human disease
human individuals may have as many as 45 CHI gene pairs
Actin Filament Assembly,
Growth, Branching, Capping
and Disassembly are
Controlled by Actin Binding
Proteins
The ARP (Actin-Related Proteins) complex
Regulates Actin Polymerization
Arp2 and Arp3 cannot form polymers due to
differences in their minus ends
Filament Elongation is Modified By
Proteins that Bind to Free Subunits
The ARP complex Binds nucleates filaments more efficiently
When bound to the side of a preexisting Actin Filament
Capping Proteins Prevent Polymerization
Actin polymerization is induced by Arp 2/3 protein complex at the surface of Listeria monocytogenes
Matthew D. Welch et al.
The pathogenic bacterium Listeria monocytogenes is capable of directed movement within the cytoplasm of infected
host cells. Propulsion is thought to be driven by actin polymerization at the bacterial cell surface and moving bacteria
leave in their wake a tail of actin filaments. Actin assembly by L. monocytogenes requires the bacterial surface protein
ActA and protein components present in host cell cytoplasm. We have purified an eight-polypeptide complex that
possesses the properties of the host-cell actin polymerization factor. The pure complex is sufficient to initiate ActAdependent actin polymerization at the surface of L. monocytogenes, and is required to mediate actin tail formation
and motility. Two subunits of this protein complex are actin-related proteins (ARPs) belonging to the Arp2 and Arp3
subfamilies. The Arp3 subunit localizes to the surface of stationary bacteria and the tails of motile bacteria in tissue
culture cells infected with L. monocytogenes; this is consistent with a role for the complex in promoting actin
assembly in vivo. The activity and subunit composition of the Arp2/3 complex suggests that it forms a template that
nucleates actin polymerization.