(英文)细胞生物学lecture6-肌动蛋白细胞骨架

GTPase activating protein
Guanine exchange factor
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Rac induced changes in actin organization
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Actin organization is regulated by small GTPases
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Movement of the intracellular pathogen Listeria monocytogenes
How does Listeria move inside their host cell?
The bacterial cell surface protein ActA is required for motility.
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ActA is sufficient for the motility of Listeria
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The regulation of a small GTPase
• small GTP binding protein • 2 different conformational states (GTP- or GDP-bound) • different nucleotide binding state is regulated by GAPs and GEFs molecular timer • localization of GAPs and GEFs provides spatial regulation of GTPase activity
The bacterial protein ActA is necessary and sufficient for actin-based motility of the bacterium. How does that help the bacterium? 15
Actin tails are commonly used to propel bacteria inside a host cell
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What does myosin II do?
Myosin head group “walks” towards the (+) end of F-actin
Motor domain:
- binds ATP - binds F-actin - conserved among all myosins
Trailing edge
Leading edge 6
The Arp2/3 complex: an actin binding complex
Arp2/3 • controls actin nucleation • leads to a branched network. 7
ARP 2/3 complex at the leading edge
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The sarcomere of a skeletal muscle
Dark Light band band Z disc M-line Z d a critical component of the muscle sarcomere
Myosin heads
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Regulators of muscle contraction
• Actin and myosin filaments are stabilized by accessory proteins • the actin-binding proteins, troponin and tropomyosin, coat actin filaments, and are the Ca2+ sensors of a sarcomere
Actin organization depends on regulatory actin binding proteins
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How do eukaryotic cells crawl?
Leading edge of a cell stained for total actin (green)
Pulse labeling of a cell with rhodamine-labeled actin (red)
Actin is nucleated at the leading edge of a migrating cell.
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The steps of cell locomotion
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A migrating cell is polarized
Crawl - during infection, chemotaxis (macrophages, neutrophils) - during development (to establish a body plan) - during injury to rebuild damaged structures (eg fibroblasts) 2
Lecture 6 The actin cytoskeleton, Part II
1. The movement of a eukaryotic cell 2. The movement of intracellular bacteria 3. Muscle contraction
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Cell movement
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How does an extracellular signal induce cell migration?
Extracellular signals lead to activation of small GTPases of the Rho family (Rho, Rac and Cdc42)
Listeriosis: - food poisoning - diarrhea Menangitis pregnant women: still birth
Cells contain actin-GFP
Actin-GFP is incorporated into the pathogen’s “Comet tail”. 13