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Lecture 16 Motor proteins and cytoskeletal-mediated cell behavior. Myosin II and myosin II bipolar thick filament. 2 heavy chains: Globular head domain (ATP) long tails (coiled coils) 2 light chains:. Bipolar thick filaments: Tail-tail interactions. Hundreds of myosin II molecules.

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Lecture 16 Motor proteins and

cytoskeletal-mediated cell behavior


Myosin II and myosin II bipolar thick filament

2 heavy chains:

Globular head domain (ATP)

long tails (coiled coils)

2 light chains:

Bipolar thick filaments:

Tail-tail interactions

Hundreds of myosin II

molecules

Thin filament: actin filament


Experimental evidence for the motor activity of the myosin head

0.6 sec apart

4 um/sec

Myosin head S1:

by chymotrypsin and papain

Attached to the glass slide


Myosin superfamily head

Similar motor domains

Move to plus end except VI

Small insertion in the motor domain


Function of myosins head

Myosin II: contractile activity in muscle and nonmuscle cells, cytokinesis

(pinching apart of a dividing cell into two daughters), forward translocation of

cell body during migration);

Myosin I: contain a second actin-binding or membrane-binding site in their tails-

Intracellular organization and the protrusion of actin-rich structures at the cell surface;

Myosin V: vesicle and organelle transport;

Myosin VII: inner ear (deafness when mutated)


Microtubule motors head

Kinesins

Dyneins: minus-end-directed

Unrelated to the kinesin superfamily

Cytoplasmic dyneins: vesicle trafficking and Golgi apparatus localization;

Axonemal dyneins: sliding movements of MT(14um/sec)

Third: cilia beating

Kinesin-related proteins, KRPs

Most of them have N-terminal motor domains walk toward plus end

One family has C-terminal motor domains and move to minus end

BimC forms bipolar motor


Cycles if structural changes in myosin head

Head-over-head movement of kinesin

5 nM


Attachment of dynein to a head

membrane-enclosed organelle

Organization of Golgi by MT

Large complex!

Colchicine or nocodazole

causes ER to collapse to center

and Golgi to fragment and disperse

Kinesin: motor protein receptors


Myofibrils under EM head

Skeletal muscle cells

(muscle fibers)

multinuclear

sarcomere

Myofibrils: 1-2 um diameter,

made of sarcomeres, 2.2 um long

Z-disc:plus end


Sliding-filament model of head

muscle contraction

300 heads

Shorten by 10% in

<1/50th sec

15 um/sec

Titin: “molecular spring”

Stable actin

filament

“Molecular ruler”

Nebulin: repeating 35 aa

actin-binding motif


The control of skeletal muscle contraction by troponin head

Troponin I-T complex

pulls the the tropomyosin

out of its normal into a

position along the actin

filament that blocks the

the binding of myosin heads

Upon Ca++ increase,

troponin C causes

troponin I to release its

hold on actin, allowing

tropomyosin to slip back so that

myosin head can walk along

the actin filament


Effect of the heart of a suble mutation in the cardiac myosin

FHC:

Inherited 2/1000: heart enlargement,

abnormal small coronary vessels,

disturbances of heart rhythm (cardiac

arryhthmias)--mutations in myosins and

Contractile proteins.

Dilated cardiomyopathy:

cardiac actin mutations--early heart failure

Familial hypertrophic cardiomyopathy

Frequent cause of sudden death

in young athletes


The arrangement of MTs myosin

in a flagella or cilium

Contrasting motions of

flagella and cilia

MT and dynein based motility structures

“9+2” arrangement

In sperm and

protozoa

Whip-like motion

of cilia

Move cells

or liquid or

other cells

Base binds to A MT

and heads bind to B MT


The bending of an axoneme myosin

The motor action causes

a bending motion, creating

waves of beating motion as

in a sperm.

Bacterial flagella don’t have

MT or dynein and do not wave

Or beat. Instead, long, rigid, helical

Filaments of repeating subunits of flagellin.

Move like propellers driven by rotary motor

in the cell wall. The name is a mistake…

Basal bodies

Kartagener’s Syndrome:

Male sterility (immotile sperm)

Higher susceptibilty of long infections

Left-right body axis defects


How basic cytoskeletal mechanisms produce complex cell behaviors

Cell shape

Migration

Division


Polarity of actin patches and cables throuhgout the yeast cell cycle

New patches

Very few cytoplasmic MT

Cables random

Actin patches are concentrated at the growing tip of the bud

Actin cables align and point toward them


Morphological polarization of yeast cells in response to mating factor

Yeast cells can’t swim

a-cell and a-cell, two mating types

Shmoo tip grow toward the highest concentration of the signal molecule




Behavior of lamellipodial fragments forward

Lamellipodia contain all of the machinery

that is required for cell motility!



Lamellipodia and ruffles at the leading edge edge

Lamellipodia that fail

to attach to the

substratum are swept

backward-- ruffling


Neutrophil polarization and chemotaxis edge

Peptide formyl Met-Leu-Phe

New lamellipodium toward the tip

Extends lamellipodium polarizes

cytoskeleton and cell moves forward


The complex morphological specialization of nerrons depends edge

on the cytoskeleton

Anterograde transport

Retrograde transport



Cytoskeleton provide the engine for construction edge

of the entire nervous system

As well as the supporting structures that strengthen, stabilize

and maintain its parts


Summary edge

Actin-based motors, microtubule motors,

their structure and function

Motility machines: myofibrils and flagella and cilia

Complex cellular behaviors mediated by cytoskeleton

Cell polarization: yeast budding and mating

Cell crawling

Morphology


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