Biophysics I 2013-2014 12/2/2014

UP MS Department of Biophysics - Beáta Bugyi 1

Biophysics I. - 2014. 02 – 03 December

Dr. Beáta Bugyi

UP MS Department of Biophysics

OVERVIEW

MUSCLE

� TYPES: STRUCTURE and FUNCTION

� STRIATED MUSCLE

� MOLECULAR BASIS FOR MUSCLE FUNCTION

� MUSCLE MECHANICS

MUSCLE

organ built from contractile tissue specialized for

� macroscopic biological motion

� nanoscopic mechanochemical system

assembled from proteins and protein networks

chemical energy � mechanical work

v

MUSCLE – TYPES

STRIATED MUSCLE SMOOTH MUSCLE

SKELETAL MUSCLEHEART MUSCLE(cardiac biophysics)

body location attached to bones or to skin

(some facial muscles), 45 %

walls of the heart visceral organs, intrinsic eye

muscles, airways, large arteries

regulation of

contractionvoluntary involuntary

(intrinsic regulatory system)

involuntary

striated pattern striated pattern no striated pattern

cell shape,

appearancevery long, cylindrical

multinucleate

branched chain of cells

uni-, binucleate

fusiform

uninucleate

Ca2+ source sarcoplasmic reticulum sarcoplasmic reticulum

extracellular fluid

sarcoplasmic reticulum

extracellular fluid

Ca2+ regulation troponin troponin calmodulin

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MUSCLE STRUCTURE – STRIATED MUSCLE

MUSCLEorgan

MUSCLE FIBERcell

MYOFIBRILorganelle

http://bursaclab.bme.duke.edu/gallery.php?id=19

striated pattern

dark (A) bright (I) band

FASCICLE

nucleus Z disc

MUSCLE STRUCTURE – SARCOMERE

H zone

M line

Z disk

thin filament

titin

thick filament

Z disk

SARCOMERE� the smallest functional (contractile) unit of muscle

� Z – Z distanve

L~ 2.2 µm

I band

isotrop/light

A band

anisotrop/dark

MUSCLE STRUCTURE – MYOFILAMENTS

THICK FILAMENT

myosin II

THIN FILAMENT

� actin

� regulatory proteins

tropomyosin, troponin, tropomodulin

Miofilaments observed by transmission electron microscopy (TEM).

(micorscopy)

THICK FILAMENT – MYOSIN II: THE MOTOR

Geeves and Holmes Advances in Protein Chemistry 2005.

3D structure of myosin II crossbridge (head&neck)

(lX-ray diffraction)

head tailneck

crossbridge

myosin II filament – THICK FILAMENT

MYOSIN II (motor proteins)

HEAD

NECK

…TAILenergy source: ATP

ATPase activity (basal)chemical energy �

strucutral change �

force generation, mechanical work

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Hild, Bugyi et al. Cytoskeleton 2010

AKTIN AKTIN AKTIN AKTIN FILAMENTUMFILAMENTUMFILAMENTUMFILAMENTUM

FFFF----AKTINAKTINAKTINAKTIN

1

2

3

4ATP-Mg2+

szöges (+) vég

hegyes (-) vég

AKTIN MONOMERAKTIN MONOMERAKTIN MONOMERAKTIN MONOMER

GGGG----AKTINAKTINAKTINAKTIN

szöges (+) vég

hegyes (-) vég

~ 5 nm

~ 8 nm

polimerizációpolimerizációpolimerizációpolimerizáció

THIN FILAMENT – ACTIN: THE TRACK

ACTIN ACTIN ACTIN ACTIN = ACTACTACTACTivatININININgACTIN ACTIN ACTIN ACTIN = ACTACTACTACTivatININININg

kép: Szent-Györgyi Albert munkacsoportja Szegeden 1933-ban. 1 – Szent-Györgyi Albert; 2 – Straub F. Brunó; 3 – Laki Kálmán; 4 – Banga Ilona

(Szent-Györgyi András szívességéből)

Brúnó F. Straub Brúnó F. Straub Brúnó F. Straub Brúnó F. Straub

Szent-Györgyi Albert’s research group: Szeged, Hungary, 1933

Ilona BangaIlona BangaIlona BangaIlona Banga

ACTO-MYOSIN CROSS-BRIDGE: MOTOR ON THE TRACK

A: actin, M: myosin II

ACTIN ACTIVATED ATPase EZYMATIC ACTIVITY – FORCE GENERATION CYCLE

A – M:ADP-Picross-bridge:attached

A – M:ADPcross-bridge:attached

Pi dissociation

ADP dissociation

M:ATPcross-bridge:detached

M:ADP-Picross-bridge:detached

POWER STROKE

force generation

~ 10 nmRIGOR

rigor mortis

RECOVERY STROKE

attachment CROSS-BRIDGE

CYCLE

ATP hydrolysis

ATP binding

detachment

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ACTO-MYOSIN CROSS-BRIDGE CYCLE in vitro MUSCLE STRUCTURE – FUNCTION

The acto-myosin filament system is a MECHANOCHEMICAL

MACHINERY, that converts CHEMICAL ENERGY through STRUCTURAL

CHANGES into FORCE GENERATION and MECHANICAL WORK.

! no force transmission, and regulation

? WHAT ELSE DO WEE NEED?

� FORCE TRANSMISSION: ANCHOR

Z and M lines / tendon

� REGULATORY COMPONENTS: STERIC BLOCKING MODEL

Ca2+ sensitive troponin – tropomiozin system

FORCE TRANSMISSION – ANCHORS – Z DISC, M LINE

Z DISK, M LINE

� thin filaments

Z disk

� thick filaments

M line

MUSCLE– TENDON – BONE

FORCE TRANSMISSION – TENDON

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SLIDING FILAMENT MODEL

Z-Z: sarcomere: shortens

I band: shortens

A band: constant

H band: shortens

Andrew.F. Huxley (1954), Hugh. E. Huxley (1954)

REGULATORY COMPONENTS – TROPOMYOSIN

� alpha helical coiled-coil dimer

� forms a polimer along the actin filament (N-C overlap: head-to-tail overlap)

� 1 tropomyosin dimer binds 7 consecutive actin subunits

Greenfield et al. JMB 2006.

PDB: 2TMA

TROPOMYOSIN

NC

3D structure of tropomyosin and structural model of the actin-tropomyosin filament.

three subunits:

TROPONIN T (tropomyosin binding)� 37 kDa

� binds tropomyosin and the other troponin subunits

� stabilizes the troponin complex

TROPONIN I (inhibitory)� 22 kDa

� inhibits the myosin II – actin interaction

TROPONIN C (Ca2+ binding)� 18 kDa

� binds Ca2+

PDB: 1TCF

TROPONIN COMPLEX

3D structure of troponinC with bound Ca2+.

REGULATORY COMPONENTS – TROPONIN COMPLEX STERIC BLOCKING MODEL

THE BINDING SITED OF MYOSIN II ARE BLOCKED / FREE

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MOLECULAR BASIS OF MUSCLE CONTRACTION

MOLECULES

� myosin II

� actin

� tropomyosin

� troponin

� Ca2+

� ATP

1. stimulus

2. [Ca2+]citoplasm↑

3. troponinC binds Ca2+

4. troponin-tropomyosin

moves on the actin filament:

free myosin II binding site

5. myosin II binds to actin

filaments

6. crossbridge cycle – ATPase

activity

7. contraction