D103 - Lecture 6 - Actin.docx

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University of California - Irvine
Biological Sciences
Grant Mac Gregor

A. Clicker a. When does treadmilling occur? b. Inhibit Rho GEF, effect? i. Cells wouldn't migrate A. Ask Professor a. Profilin stays bound to G-Actin? B. Question a. Find value of Cc given the rate of on and the rate of off B. Actin binding proteins a. Thymosin i. Sequesters ATP-G-Actin b. Cofilin i. Binds ADP-actin, accelerates disassembly b. Profilin i. Stay bound with ATP G- Actin b. Formin Proteins i. A family of proteins ii. Has regulatory domain, and has FH1 and FH2 (fomin homology Domain) iii. Inactive - folded iv. Active - small GTPase (Rho) binds and activates the protein v. FH1 1. Binds Profilin ATP actin 2. Binds over to FH2 ii. FH2 1. Binds to the plus end of F-actin ii. FH1 and FH2 domains forms a donut 1. Dimer 2. Actin is a helix, 2 filaments b. Arp2/3 i. Actin related protein 1. Look similar to actin ii. Nucleating complex, binds alongside a preexisting filament 1. At 70 degrees, branch ii. Inactive by itself 1. Requires nucleation promoting factor a. WASp i. ACW subuits 1. W - binds to subunits 2. A - binds to ARP2/3 ii. Disease 1. Wiskott-Aldrich Syndrome a. Defective WASp factor b. Low platelet count c. Immunodeficiency b. Capping Proteins i. Binds at plus or minus ends ii. Protect from depolymerization iii. Important in muscle fibers iv. CapZ 1. Z line 2. At the plus end ii. Tropomodulin 1. Minus end B. Myosin a. Type 2 myosin b. Found in muscle fibers c. Forms a homodimer d. Actin-binding molecular motors e. Type 5 i. More accessory proteins ii. Transport of vesicles b. Head domain i. Conserved among all myosins b. Tail domain i. Specific for each myosin b. Myosin walks toward the plus end of actin B.
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