9/11 Contractile Proteins Flashcards
Actin-Based Cellular Structures
- Actin is a major component of ______
- Dozens of proteins organize actin filaments into a diverse group of functional structures
cytoskeleton
Actin-Based Cellular Structures
• Actin filaments are assembled via accessory proteins into two general types of structures
– Actin bundles • Cross-linked into closely packed ____arrays
– Actin networks • Loosely cross-linked in ____ arrays that form three-dimensional meshwork with gel-like properties
– Each underlies a specific function
parallel
orthogonal
Cross-linking of F-actin achieved by peptides and polypeptides having at least _____(#) actin-binding sites
Nature of association of filaments determined by ____ and ___ of the crosslinking proteins
Bundling proteins are typically small, ridged proteins that force the filaments to align closely with each other
*parallel arrays
two
size and shape
One type of bundle includes closely spaced actin filaments in parallel
– Supports projections of plasma membrane (ex. Microvilli)
– Filaments have the ____ polarity
– ____ binds to actin filaments as a monomer, holds two parallel filaments close together
same
fimbrin
Actin-Bundling Proteins
Actin filaments can be loosely bundled
– Called ＿＿＿＿• Ex. Contractile ring used in mitosis – Looseness reflects structure of crosslinking proteins
• Ex. α-actinin • Binds as a _____• Filaments separated by a greater distance • Allows motor protein (myosin) to interact during contraction
contractile bundles
Dimer
Actin-Bundling Proteins
Actin filaments in networks held together by large actin binding proteins
– i.e. ____ – Binds actin as a ___ – Actin binding domains located on opposite ends of dimer – Can create three-dimensional meshwork
filamin
dimer
Actin Interactions with Plasma Membrane
• Three dimensional networks are abundant _____ the plasma membrane
– Determine ____ of cell, aid in movement, stability/flexibility of membrane
• Erythrocytes contain actin binding protein ____
– Tetramer which associate laterally
– Form actin network that forms a cortical cytoskeleton
– Spectrin-actin network interacts with membrane proteins via interactions with ankyrin, protein 4.1
beneath
shape
spectrin
Actin Interactions with Plasma Membrane
Hereditary spherocytosis, is caused by which mutation?
-Mutations in cortical cytoskeleton proteins in erythrocytes (Spectrin, ankyrin, 4.1)
– Flexibility and stability of RBCs • Movement from large vessels to capillaries required
– Decreased RBCs (anemia)
– Jaundice
– Splenomegaly
– Abnormally shaped red blood cells
Actin Projections and Plasma Membrane
_____ based on actin filaments crosslinked into a three-dimensional network, that are responsible for phagocytosis
____broad, sheet like extensions at the leading edge of cell, containing a network of actin filaments.
______ thin projections of the plasma membrane supported by actin bundles. The formation and retraction of these structures is based on the regulated assembly and disassembly of actin filaments
Pseudopodia
Lamellipodia
Filopodia
*growth at the + end, remove the projection at the - end
myosin
- Superfamily of motor proteins – 20 different myosin types in eukaryotes – All move along actin filaments via ____
- Skeletal muscle myosin II – _____ filaments – Tails associate to form shaft of filament – Heads exposed at both ends
ATP hydrolysis
Bipolar (the common muscle myosin)
Myosin: Actin-based Motor Proteins
Myosins have 3 major domains, which are?
– Head • Contain actin binding and ATP binding sites • ATPase activity
– Neck • Flexible region • Binds myosin light chain peptides
– Tail • Intertwine to bring myosin head regions in close proximity • Bind membrane/organelles
myosin I to III
Myosins Move along F-Actin
Velocity Dependent on Length of Neck
Powerstroke mechanism is proportional to length of neck domain – _____neck domain, increased rate of movement
Longer
the interaction between actin and myosin
+ end is associated with which element?
Z disk
Smooth and Non-Muscle Cell Contractions
When Ca2+ increases, what happens to the MLC kinase? what happens to the smooth muscle?
activated
contraction and assemble
Smooth and Non-Muscle Cell Contractions
- Non-muscle cells contain several types of actin-myosin structures similar to skeletal muscle fibers – Much less stable or organized
- Some are transient interactions – _____: • Bundles of f-actin and myosin II form ______• Myosin movement along actin filaments creates _____
Cytokinesis
contractile ring
cleavage furrow
Vesicular Transport, is involved in which class of myosin?
which direction does myosin V moving towards to? what about myosin VI?
5
+ and - end
cell migration
Duchene Muscular Dystrophy (DMD)
Mutations within ______ Gene, and what type of deletion?
Hundreds of Mutations are found, mostly large internal ___ type mutation
Milder form w/ later onset is? what type of deletion?
Dystrophin, out of frame deletion
deletions
Becker Muscular Dystrophy (BMD), in-frame deletion
Schematic Diagram of Proteins Involved in Lateral and Longitudinal Force Transfer
Organization of the Dystrophin-Glycoprotein Complex in Skeletal Muscle
The dystrophin-glycoprotein complex provides a structural link between the cytoskeleton of the muscle cell and the extracellular matrix, which appears to stabilize the sarcolemma and hence prevents contraction induced injury (rupture). Duchenne’s muscular dystrophy is associated with loss of dystrophin.
