Molecular Motors - Duke University

Molecular Motors - Duke University

Molecular Motors Lecture 33 ` BSCI 420/421

Nov 18, 2002 To survive the 21st century, our thinking must be creative and humane as well as analytical. - Robert Kuhn

1. Myosins 2. Kinesins 3. Dyneins Myosins

Are a family of motor proteins that bind to & move along ac filaments toward the + ends. Large globular heads bind and split ATP Undergo a configurational change that changes the angle

of the head with respect to an -helical tail. E.g. Myosin II Myosin II of vertebrate muscle The Myosin family portrait

N--------------------------------C In vitro motility assay: Evidence of myosins motor activity (Fig. 53) (wrong way)

X-ray crystal structures of myosin & kinesin heads Myosin cross-bridge cycle Skeletal Muscle fibers are multinucleate muscle cells

formed by fusion of myoblasts. (fig 68) Sarcomere structure of myofibrils, dark=A band, light=I ban X-sec of myofibril, insect flight muscle, verts slightly differe

(Fig.70) Sliding filament model (Fig.71) -actinin

MT-based Motors: Kinesin & Dynein Kinesin is a large protein with 4 polypeptide chains Like myosin it has 2 heavy chains, each w a globular head domain and long -helical tail.

2 light chains on cargoMT binding end binding (vary in diff.

cells w diff. cargo) ATP-binding site Coiled-coil in each head tail

Kinesins + + 2 HC in tail

KIFs Kinesin Family members +

FreezeEtched, Shadowed TEM

+ Comparison of kinesin and myosin mechanochemical cycles 3. Dyneins are a family of minus end directed MT motors.

Largest and fastest molecular motors (14 m/sec vs 2 m/sec for kinesin)(fig 56) Dynein moves vesicles and the Golgi app toward the cell center.

A) Untreated B) Nocodazole Fig. 62

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