Dynamic Dissonants Cell and Developmental Biology New York University David Scicchitano Mark Siegal Kris Gunsalus University of Hawaii Steve Robinow Athula Wikramanayake University of Wisconsin, Madison Brian Manske

Part I: structure, assembly and dynamics of microfilaments Part II: the cytoskeleton organizes the cytosol and supports the function of other cellular organelles and processes Part III: cytoskeletal filaments form higher-order structures that perform diverse functions Actin Cytoskeleton Teachable Unit

Chemical principles govern the behavior of biological macromolecules. Cellular phenomena reflect the collective action of populations of molecules. The same molecule can have multiple, diverse functions within cells. Teaching Challenges

Diseases of the cytoskeleton Muscular Dystrophy Dystrophin – muscular degeneration Kartagener Syndrome Axonemal dynein intermediate chain – Infertility due to defective sperm motility – Situs inversus Usher Syndrome myosin VII – deafness Epidermolysis bullosa and bullosa pemphigoid keratin mutation or autoimmune disorder – skin blistering Actin Microtubules Intermediate filaments

Are microfilaments the same as F-actin? A. Yes B. No

What polymerizes to form microfilaments? A. alpha-tubulin B. intermediate filaments C. beta-tubulin D. G-actin

The cytoskeleton is composed of: A. microtubules B. microfilaments C. intermediate filaments D. A and B E. A and C F. B and C G. A, B, and C

Are microfilaments the same as F-actin? A. Yes B. No What polymerizes to form microfilaments? A. alpha-tubulin B. intermediate filaments C. beta-tubulin D. G-actin The cytoskeleton is composed of: A. microtubules B. microfilaments C. intermediate filaments D. A and B E. A and C F. B and C G. A, B, and C

Are microfilaments the same as F-actin? A. Yes B. No What polymerizes to form microfilaments? A. alpha-tubulin B. intermediate filaments C. beta-tubulin D. G-actin The cytoskeleton is composed of: A. microtubules B. microfilaments C. intermediate filaments D. A and B E. A and C F. B and C G. A, B, and C

synonymous to

Learning Goals To understand the structure, assembly and dynamics of microfilaments Apply chemical principles to enhance understanding of actin polymerization Predict and understand a biological model of actin polymerization Predict and interpret experimental results

G-actin: globular monomer F-actin: filamentous polymer G-actin  F-actin

Experiment G-Actin + ATP G-Actin I Results F-actin is present in I only (at steady state) II

Additional Experiment G-Actin + ATP* G-Actin + ADP A. No F-actin in either B. F-actin in both C. F-actin in I D. F-actin in II ATP* cannot be hydrolyzed to ADP I II

Actual Results G-Actin + ATP G-Actin + ATP* G-Actin + ADP Amount of F-actin at steady state

Conclusion For G-actin to form F-actin: A. ATP hydrolysis is necessary. B. ATP is necessary. C. ADP is necessary. D. Either ATP or ADP is necessary. E. Neither ATP nor ADP is needed.

APPPAPPP APPAPP F-actin G-actin Fast Slow

Summary 1.G-Actin has four lobes and an ATP binding site 2.In a test tube, add magnesium, sodium, potassium and either ATP or ADP: G-actin  F-actin 3. ATP binding to G-actin provides the best conformation to promote F-actin assembly 4. F-actin has directionality (the two ends are not the same)

G-actin ↔ F-actin ATP

Actin Dynamics ATP

G-actin ↔ F-actin ATP

Summary G-actin and F-actin will reach a steady state. The nucleation step is slow.

Acknowledgements Thanks to our facilitators! Randy Phillis Lauren Gollahon