Intermediate Filaments Flashcards
The Intermediate Filament Multigene Family:
Type I: Keratins 9-20 (Acidic), Epithelials cells e.g. desmosomes
Type II: Keratins 1-8 (Basic), Epithelials cells e.g. desmosomes
Type III: Desmin, Vimentin, GFAP, skeletal muscles e.g. Desmin surrounds the sarcomere
Type IV: Neurofilaments, Axon organisation
Type V: Lamins, Nuclear structure and organisation
Type VI: Filensin
All have similar secondary structure (alpha helical coiled coils)
Intermediate Filaments are Polar.
TRUE OR FALSE
FALSE
Intermediate filaments are apolar. They exchange subunits along the whole filament.
Structure of Intermediate Filaments
Head domain: essential for filament assembly
Alpha-helical rod domain: assembles in parallel dimers then antiparallel tetramers (Between head and tail domains). Then 8 tetramers are twisted into a rope-like filament.
Tail domain: contributes to filament assembly
Heptad repeats
A type of tandem repeat sequence in which a group of seven amino acids occurs many times in a protein sequence.
They form the basis of coiled-coil formation in intermediate filament protein dimers.
Intermediate filaments are difficult to bend, but are susceptible to stretching.
TRUE OR FALSE
FALSE
Intermediate filaments resist stretching but are easily bent.
Due to having staggered long subunits (Like long bricks). They have 8 tetramers twisted into a rope-like filament.
Keratin intermediate filament proteins:
Type I Proteins: Acidic isoelectric points (pH at which the molecule has no net charge)
Type II Proteins: Neutral or basic isolelectric points
Equimolar association of Type I and II required for assembly
Specific paired expression in tissues.
Intermediate filament attachment sites:
Keratins: Desmosomes and Hemidesmosomes
Type III: Desmosomes (Desmin/GFAP)
What happens when intermediate filaments fail? (In terms of disorders)
Skin blistering disorders arise (such as Epidermolysis bullosa simplex)
Intermediate filaments in the nucleus:
Lamin (Type V) intermediate filaments are all intranuclear.
A-lamins in differentiated cells.
B-lamins in all nuclei.
Disassembly/reassembly of the nuclear lamina by phosphorylation at mitosis.