intermediate filaments Flashcards
important differences between intermediate filaments (IFs) and actin/microtubules
- IFs don’t interact with motor proteins
- IFs don’t have intrinsic polarity (no plus/minus)
- IFs don’t bind ATP or GTP
- IFs don’t possess any enzymatic activity
- IFs are not present in all eukaryotic cells
basically, IFs are less dynamic, more stable, than actin/microtubules
where are IFs found? which types of cells
found in some animals, only vertebrates and other soft-bodies metazoans (not sponges). Insects have one kind of IF (nuclear laming) but otherwise use chitin instead
IFs are prominently expressed in the cytoplasm of cells subjected to mechanical stress. Also present in nucleus
what is the structure of intermediate filaments?
individual monomers have elongated alpha helical domain with non helical ends. monomers form coiled-coil dimers. dimers form anti-parallel tetramers. tetramers bundle to form rope-like intermediate filament.
which filaments are the strongest and weakest?
microtubules are weakest, then actin, then intermediate filaments are strongest. The lateral bonds of the subunits and the rope bundle make IFs able to handle higher stress forces
what types of accessory proteins do intermediate filaments have?
cross-linking
bundling
how do neuron IFs bundle?
IFs can self bundle into neurofilaments. neighbors link together due to elongated C-termini
what is plectin?
Plectin is a cross linker protein that makes bundles of vimentin (type of IF). Plectin links IFs to other types of cytoskeletal elements (microtubules, actin filament bundles, myosin II filaments)
what are the 6 types of IFs?
- Acidic keratins
- Basic keratins
these two types form obligate heterodimers. a Type I monomer must associate with a type II - Vimentin-like IFs
- Neurofilaments
- Lamins
- Eye lens IFs
Epithelial keratins are important in epithelial cells, about 50 genes encode keratins. What can mutations of epithelial keratins cause?
serious skin diseases. Epidermolysis Bullosa Simplex (EBS) causes tissue fragility that manifests as blistering even though the skin is not stressed. Blistering results form rupture of the basal cell layer of epidermis where keratin connections are broken
what are desmosomes?
keratin connections between cells
what are hemidesmosomes?
keratin connections between cells and the extracellular matrix/basal lamina
epithelial keratin is one main type of keratin. what is the other main type?
Trichocytic keratin or hair keratins. these are present in hair, bur, fingernails, reptilian scales, avian feathers, bear claws, bird beaks, and rhino horns
what are neurofilaments and what disease is associated with them?
IFs found in axons of neuronal cells, convey longitudinal strength to axon.
ALS (Lou Gehrig’s disease) is an accumulation and abnormal assembly of neurfilaments in signal motor neurons. May trigger death of spinal motor neurons. ALS patients lose voluntary muscle contraction until they become paralyzed
what are lamins?
most ancient class of IFs (ancestral type) found in the nuclear lamina of nuclear envelope (in all eukaryotes)
what do mutations of lamins cause?
Emery-Dreifuss Muscular Dystrophy (EDMD): altered versions of lamin A and C
Dilated Cardio-Myopathy (DCM): mutations in lamin A/C or Emerin
Hutchinson-Gilford Progeria Syndrome: cell nucleus has dramatically aberrant morphology (very crinkled)
