Contractile Proteins

Front 1

Contractile Apparatus in Skeletal Muscle

Back 1

Thin and thick filaments, 3 ml wide with tapered ends
Every myosin is surrounded by 6 actin strands which is referred to as Interdigitated

Front 2

Components of myosin

Back 2

Four Light Chains, Two Heavy Chain, Two globular heads, Rod Domain (helix) MAKING UP ABOUT 35% of Muscle Protein
One thick filament will have 600 head groups which pull the thin filament to the M line

Front 3

Function of Myosin

Back 3

Myosin heads hydrolyze atp for mechanical movement and they self assemble at the tail ends
Myosin heads arranged at 30 degrees rotational symettry with thin filaments surrounding them at 60degrees

Front 4

Myosin Fragments

Back 4

Proteases can cleave myosin at certain spots: papain and typsin make S1 and S2 fragments

Front 5

S1 Fragment and Light chain

Back 5

Has two light chains, p loop, actin binding site, and nucleotide binding site exhibiting a p loop atpase domain

Light chains act like calmodulin (smooth muscle) and bind the alpha helix by wrapping around it.

This fragment also has different conformation depending on what is attached to it which allows the powerstroke to occur based on ATP hydrolysis

Front 6

Actin: componenets

Back 6

Actin has a positive barbed end anchored to the Z disks and a negative pointy end which goes towards the M line.
The polarity is in such a way that actin heads will not bind with each other during a muscle contraction
Has nucleotide binding sites which allow for interaction: these interactions (and hydrogen binding) allow for bonding

Front 7

Actin Synthesis and Formation

Back 7

G Actin assembles into F actin (filamentous) in a double helical arrangement.
Each G actin interacts with four neighbors and the growing/final filament has directionality
ATP binds to free actin first and the mature filament has ADP bound to monomeric G Actin Units

Front 8

Tropomodulin, Capz, Nebulin: what do they do

Back 8

Tropomodulin caps the minus end to prevent more polymerization of F actin

CapZ (beta actinin) associated with alpha actinin to cap the plus end (z disk end)

Nebulin acts as a ruler and template for actin polymerization

Front 9

Troponin T, I, and C on the thin filament

Back 9

Troponin T - binds tropomyosin and positions the complex on the filament

Troponin I - binds actin and inhibits myosin binding

Troponin C - binds calcium and relieves inhibition

Front 10

Tropomyosin and troponin complex

Back 10

Tropomyosin has a coiled structure, wrapped and attached to the groove of the actin molecule.

The troponin complex is periodic and sits at certain parts

The heart has isoforms of the troponin complex and during a heart attack, due to the change in conformation of cells and permeability, will leak small molecules first: therefore troponin in the blood is indicative of a heart attack

Front 11

M protein: Myomesin
Alpha Actinin
Titin

Back 11

Myomesin helps provide arrangement at the M line
Alpha Actinin helps maintain architecture of the z disk and works with Beta Actinin to cap the z(plus) end of Actin
Titin is the biggest protein: acts as a molecular ruler, useful for muscle development, helps balance forces across a sarcomere, provides passive elasticity and muscle signaling. Helps the muscle pop back to the ready state

Front 12

Dystrophin

Back 12

Dystrophin is the biggest gene on planet
Dystrophin gene codes for the 427kDa protein, which is a rod-like protein that connects the cytoskeleton to basal lamina and stabilizes the membranes and participates in calcium handling.
C terminal Variability occurs from alternative exon splicing and N terminal variability occurs from alternative transcription initiation sites

Front 13

Duchenne Muscular Dystrophy
Becker Muscular Dystrophy

Back 13

DMD- no detectable dystrophins at all
BMD- dystrophins of various sizes

Mostly caused by exon deletion and less commonly exon duplication

Front 14

Desmin and Synemin

Back 14

Synemin and Desmin both work together to help anchor the myofibril at the zdisk

Front 15

Molecular Basis of Contraction (the simple version)

Back 15

Tropomyosin blocks myosin binding site on Actin
When calcium is introduced, the tropomyosin will come off of the myosin binding site and now the myosin binding site will be exposed. This allows myosin to bind to actin

Front 16

Smooth Muscle Contraction

Back 16

1. Calmodulin binds with Calcium
2. The calmodulin/calcium complex will bind with myosin light chain kinase and activate the myosin light chain kinase
3. This activated complex will phosphorylate Myosin and this phosphorylation will initiate the contraction and activate myosin ATPase
4.

Front 17

Myosin Power Stroke

Back 17

1. Atp binds to myosin and this causes myosin to dissociate from actin
2. Myosin will hydrolyze ATP, changing the conformation again and bringing it to a cocked position
3. When the phosphate from the hydrolyzed ATP is dissociated, the myosin head will reassociate with actin at a new position
4. when the final ADP is dissociated, a power stroke will occur

Front 18

Adenylate Kinase Reaction: roll in AMP mediated muscle glycogenolysis and glycolysis

Back 18

As muscle contracts, ATP is converted to ADP and P. in the Adenylate kinase reaction, two ADP molecules will react to form ATP and AMP. ATP will be used for contraction and AMP will activate glycogenolysis and glycolysis

Front 19

AMP and phosphate mediated muscle glygogenolysis

Back 19

Muscle Glygogen Phosphorylase, made up of two identical subunits is activated by AMP.
AMP will bind to an allosteric site, causing a change in the active site which will increase enzyme activity
Also, phospohorylation of a specific serine residue can cause a change to the active site which will increase enzyme activity as well (done via inorganic phosphate Vasu thinks, but will double check/probably isn't important)

Front 20

AMP mediated muscle glycolysis

Back 20

Acetyl CoA carboxylase 2 (ACC-2) will convert AcetylCOA to malonylCOA which inhibits CPT1 preventing Fatty AcylCOA from entering.

AMP will come and activate AMP-PK which will phosphorylate and INACTIVATE ACC-2 and phosphorylate (this will prevent more MCoA from forming) and ACTIVATE malonylCOA decarboxylase (MCoADC) (which will help convert MCoA into AcetylCoA)

This will ALL make CPT1 functional and allow acylCoA to enter into the mitochondria