Cytoskeleton
Cytoskeleton
Made up of protein filaments.
Important for structure and movement within the cell.
All cells have some form of cytoskeleton.
Focus on mammalian cells.
Filaments
Three types of cytoskeletal filaments
Intermediate filaments (intermediate size)
Microtubules (largest filaments)
Actin filaments (smallest filaments, historically called microfilaments)
Intermediate filaments give cells strength and stability against stress (twisting, turning, pulling).
Microtubules are involved in the movement of materials, support cell shape, enable movement of structures, and move chromosomes during mitosis.
Actin filaments are involved in cell shape, motility, contraction, and cytokinesis.
Intermediate Filaments
Strongest cytoskeletal filament.
Intermediate in size.
Protect cells against stress.
Involved in cell-cell junctions (desmosomes).
Reinforce the nuclear envelope.
alpha Helical
Primarily alpha-helical structure.
Form coiled-coil motifs (common in fibrous proteins).
Regions closest to n and c terminus are unstructured.
Have rope like structures that are like tough rope.
Dimeric coil-coil formed by two monomers' alpha helices winding around each other.
Tetramer
Two dimeric coil-coils form a tetramer.
They are antiparallel (run in opposite directions N to C).
Tetramer has overhangs at either end.
Noncolvalent Interactions
All interactions besides primary sequence are noncovalent.
All of these interactions besides the primary sequence of amino acid, they're all noncovalent interactions.
Bundle of Tetramers
Tetramers associate noncovalently to form a bundle of eight tetramers.
This comprises 32 monomers.
Assembly
Eight tetramers line up and interact noncovalently, creating longer and longer filaments.
Intermediate filaments are nonpolar (ends are the same).
Are not polar, just because the positive end of one and the negative end of the other cancel out.
This structure is a rope-like structure, even though there's lot covalent interactions between these arrays of eight tetramers.
If there isn't covalent interactions, you still make a strong interaction.
TEM
Spontaneous process and assemble to form structures or grow.
Classes of Intermediate Filaments
Different cell types have different intermediate filaments.
Coiled-coil domains are conserved across types.
Differences primarily in the overhangs.
In most cells, one has keratin filaments and are in epithelial cells and mementin also, which is related filaments. These are most connective tissue, blood tissues, muscle cells. nerve cells have a lot of filaments. Nuclear membrane has nuclear lamins that stabilize the structure.
Keratins
Present in epithelial cells.
50 different keratin cells exist in the human body.
Involved in cell-cell junctions.
Secreted by cells (ex: nail bed).
Also spread throughout the whole cell.
Neurofilaments
Present in nerve cells, especially in axons.
Provide structure to the axon.
Increased neurofilaments correlate with ALS and neurodegeneration.
Bundle will have problems, if we have too many of them for structure.
Nuclear Lamina
Located under the nuclear envelope.
Offer structure and support to the nuclear envelope.
Broken down by phosphorylation during cell division and reassembled by dephosphorylation.
Other Mutation
Causes the increase of progeria and rapid aging.
Increase problems with cell.
Cytoskeleton Binding Proteins
Connect intermediate filaments to other cytoskeletal filaments.
Example: plectin (connects microtubules and intermediate filaments).
We also have cash domain proteins and sun domain proteins that connect inside and outside of nucleus. It binds to lectin and micro-domain cell within nucleus.