3HH3 module 1 lecture 4-post

3HH3 module 1 lecture 4-post - I ntermediate filaments...

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Intermediate filaments: structure and function Lodish et al., 5-29 Intermediate filaments (IFs) are rope-like fibers that are made of large and heterogeneous family of proteins Diameter: 10 nm
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Unlike AFs and MTs that are present in all eukaryotic cells, IFs are present in only animal cells and not in plants and fungi. The lamins of the nuclear envelope may have been the first intermediate filaments to evolve. These are the most ubiquitous group of IFs as they are found in the nucleus. There are different types of IFs - some are restricted in their localization, not present in all cell types. The main function of IFs appears to be to impart physical strength to cells and tissues. IFs are usually associated with cell membranes (like AFs).
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http://www.interfil.org/proteins.php Intermediate filaments have been categorized based upon DNA and amino acid sequence. There are six sequence homology group: type I to type VI. 4
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Alberts et al., 16-17 Filament networks were exposed to a shear force in a viscometer and the resulting stretch was measured. AFs and MTs rupture when stretched beyond 150% of their original length (red starburst). IFs withstand large stress and do not rupture. IFs withstand stress
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Actin and tubulins subunits are highly conserved in eukaryotes, but IF proteins are widely divergent While IFs are different in structure, they show a similar mechanism of assembly. This mechanism is different from that seen in AFs and MTs. IF subunits are α -helical rods that assemble into rope-like filaments IF assembly does not involve ATP or GTP and its hydrolysis Source: Human Intermediate Filament Databasex Helix = about 40 heptad repeats that form the amphipathic helices of the coiled-coil motif HEAD TAIL
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Different IFs are expressed in different cell types Humans have more than 65 different IF proteins that are differentially expressed in complex pattern during embryonic development Highly stable and insoluble components of human cells S 3 IFs can assemble in three different ways . ..
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Cytoplasmic IFs Assembly groups 1 and 2 All IFs share a common tripartite secondary structure plan: a central, largely α -helical “rod” domain that is flanked by non- helical N- and C-terminal end domains. The homodimers or heterodimers are formed by alignment of two IF monomers alongside one another in the same orientation. The rod domains in dimers are intertwined, in a left-handed superhelix, creating a coiled-coil structure. Two dimers are assembled into an anti-parallel, staggered
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3HH3 module 1 lecture 4-post - I ntermediate filaments...

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