Summary: Intermediate filament head (DNA binding) region
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Intermediate filament Edit Wikipedia article
|Intermediate filament tail domain|
structure of lamin a/c globular domain
|Intermediate filament protein|
human vimentin coil 2b fragment (cys2)
|Intermediate filament head (DNA binding) region|
Intermediate filaments (IFs) are cytoskeletal components found in metazoan cells. They are composed of a family of related proteins sharing common structural and sequence features. Intermediate filaments have an average diameter of 10 nanometers, which is between that of 7 nm actin (microfilaments), and that of 25 nm microtubules, although they were initially designated 'intermediate' because their average diameter is between those of narrower microfilaments (actin) and wider myosin filaments found in muscle cells. Most types of intermediate filaments are cytoplasmic, but one type, the lamins, are nuclear.
The structure of proteins that form IF was first predicted by computerized analysis of the amino acid sequence of a human epidermal keratin derived from cloned cDNAs. Analysis of a second keratin sequence revealed that the two types of keratins share only about 30% amino acid sequence homology but share similar patterns of secondary structure domains. As suggested by the first model, all IF proteins appear to have a central alpha-helical rod domain that is composed of four alpha-helical segments (named as 1A, 1B, 2A and 2B) separated by three linker regions. 
The N and C-termini of IF proteins are non-alpha-helical regions and show wide variation in their lengths and sequences across IF families. The basic building-block for IFs is a parallel and in-register dimer. The dimer is formed through the interaction of the rod domain to form a coiled coil. Cytoplasmic IF assemble into non-polar unit-length filaments (ULF), which then assemble into longer structures. Part of the assembly process includes a compaction step, in which ULF tighten and assume a smaller diameter. The reasons for this compaction are not well understood, and IF are routinely observed to have diameters ranging between 6 and 12 nm.
The N-terminal "head domain" binds DNA. Vimentin heads are able to alter nuclear architecture and chromatin distribution, and the liberation of heads by HIV-1 protease may play an important role in HIV-1 associated cytopathogenesis and carcinogenesis. Phosphorylation of the head region can affect filament stability. The head has been shown to interact with the rod domain of the same protein.
The anti-parallel orientation of tetramers means that, unlike microtubules and microfilaments, which have a plus end and a minus end, IFs lack polarity and cannot serve as basis for cell motility and intracellular transport.
 Biomechanical properties
IFs are rather deformable proteins that can be stretched several times their initial length. The key to facilitate this large deformation is due to their hierarchical structure, which facilitates a cascaded activation of deformation mechanisms at different levels of strain.
There are about 70 different genes coding for various intermediate filament proteins. However, different kinds of IFs share basic characteristics: In general, they are all polymers that measure between 9-11 nm in diameter when fully assembled.
IF are subcategorized into six types based on similarities in amino acid sequence and protein structure.
 Types I and II - Acidic and Basic Keratins
- epithelial keratins (about 20) in epithelial cells (image to right)
- trichocytic keratins (about 13) (hair keratins), which make up hair, nails, horns and reptilian scales.
Regardless of the group, keratins are either acidic or basic. Acidic and basic keratins bind each other to form acidic-basic heterodimers and these heterodimers then associate to make a keratin filament.
 Type III
- Desmin IFs are structural components of the sarcomeres in muscle cells.
- GFAP (glial fibrillary acidic protein) is found in astrocytes and other glia.
- Peripherin found in peripheral neurons.
- Vimentin, the most widely distributed of all IF proteins, can be found in fibroblasts, leukocytes, and blood vessel endothelial cells. They support the cellular membranes, keep some organelles in a fixed place within the cytoplasm, and transmit membrane receptor signals to the nucleus.
 Type IV
- Neurofilaments - the type IV family of intermediate filaments that is found in high concentrations along the axons of vertebrate neurons.
 Type V - Nuclear Lamins
Lamins are fibrous proteins having structural function in the cell nucleus.
In metazoan cells, there are A and B type lamins, which differ in their length and pI. Human cells have three differentially regulated genes. B-type lamins are present in every cell. B type lamins, B1 and B2, are expressed from the LMNB1 and LMNB2 genes on 5q23 and 19q13, respectively. A-type lamins are only expressed following gastrulation. Lamin A and C are the most common A-type lamins and are splice variants of the LMNA gene found at 1q21.
These proteins localize to two regions of the nuclear compartment, the nuclear lamina—a proteinaceous structure layer subjacent to the inner surface of the nuclear envelope and throughout the nucleoplasm in the nucleoplasmic "veil".
Comparison of the lamins to vertebrate cytoskeletal IFs shows that lamins have an extra 42 residues (six heptads) within coil 1b. The c-terminal tail domain contains a nuclear localization signal (NLS), an Ig-fold-like domain, and in most cases a carboxy-terminal CaaX box that is isoprenylated and carboxymethylated (lamin C does not have a CAAX box). Lamin A is further processed to remove the last 15 amino acids and its farnesylated cysteine.
During mitosis, lamins are phosphorylated by MPF, which drives the disassembly of the lamina and the nuclear envelope.
 Type VI
 Cell adhesion
 Associated proteins
Filaggrin binds to keratin fibers in epidermal cells. Plectin links vimentin to other vimentin fibers, as well as to microfilaments, microtubules, and myosin II. Kinesin is being researched and is suggested to connect vimentin to tubulin via motor proteins.
Keratin filaments in epithelial cells link to desmosomes (desmosomes connect the cytoskeleton together) through plakoglobin, desmoplakin, desmogleins, and desmocollins; desmin filaments are connected in a similar way in heart muscle cells.
 Diseases arising from mutations in IF genes
- Epidermolysis bullosa simplex; K5 or K14 mutation
- Laminopathies are a family of diseases caused by mutations in nuclear lamins and include Hutchinson Gilford Progeria Syndrome and various lipodystrophies and cardiomyopathies among others.
- Human Intermediate Filament Database(HIFD), a comprehensive database of human intermediate filament proteins, their associated variations and diseases.
- Ishikawa H, Bischoff R, Holtzer H (September 1968). "Mitosis and intermediate-sized filaments in developing skeletal muscle". J. Cell Biol. 38 (3): 538–55. doi:10.1083/jcb.38.3.538. PMC 2108373. PMID 5664223.
- Herrmann H, Bär H, Kreplak L, Strelkov SV, Aebi U (July 2007). "Intermediate filaments: from cell architecture to nanomechanics". Nat. Rev. Mol. Cell Biol. 8 (7): 562–73. doi:10.1038/nrm2197. PMID 17551517.
- Hanukoglu I, Fuchs E (November 1982). "The cDNA sequence of a human epidermal keratin: divergence of sequence but conservation of structure among intermediate filament proteins". Cell 31 (1): 243–52. doi:10.1016/0092-8674(82)90424-X. PMID 6186381.
- Hanukoglu I, Fuchs E (July 1983). "The cDNA sequence of a Type II cytoskeletal keratin reveals constant and variable structural domains among keratins". Cell 33 (3): 915–24. doi:10.1016/0092-8674(83)90034-X. PMID 6191871.
- Lee CH, Kim MS, Chung BM, Leahy DJ, Coulombe PA (July 2012). "Structural basis for heteromeric assembly and perinuclear organization of keratin filaments". Nat. Struct. Mol. Biol. 19 (7): 707–15. doi:10.1038/nsmb.2330. PMID 22705788.
- Qin Z, Kreplak L, Buehler MJ (2009). "Hierarchical structure controls nanomechanical properties of vimentin intermediate filaments". PLoS ONE 4 (10): e7294. doi:10.1371/journal.pone.0007294. PMC 2752800. PMID 19806221.
- Wang Q, Tolstonog GV, Shoeman R, Traub P (August 2001). "Sites of nucleic acid binding in type I-IV intermediate filament subunit proteins". Biochemistry 40 (34): 10342–9. doi:10.1021/bi0108305. PMID 11513613.
- Shoeman RL, Huttermann C, Hartig R, Traub P (January 2001). "Amino-terminal polypeptides of vimentin are responsible for the changes in nuclear architecture associated with human immunodeficiency virus type 1 protease activity in tissue culture cells". Mol. Biol. Cell 12 (1): 143–54. PMC 30574. PMID 11160829.
- Takemura M, Gomi H, Colucci-Guyon E, Itohara S (August 2002). "Protective role of phosphorylation in turnover of glial fibrillary acidic protein in mice". J. Neurosci. 22 (16): 6972–9. PMID 12177195.
- Parry DA, Marekov LN, Steinert PM, Smith TA (2002). "A role for the 1A and L1 rod domain segments in head domain organization and function of intermediate filaments: structural analysis of trichocyte keratin". J. Struct. Biol. 137 (1-2): 97–108. doi:10.1006/jsbi.2002.4437. PMID 12064937.
- Quinlan R, Hutchison C, Lane B (1995). "Intermediate filament proteins". Protein Profile 2 (8): 795–952. PMID 8771189.
- Herrmann H, Bär H, Kreplak L, Strelkov SV, Aebi U (July 2007). "Intermediate filaments: from cell architecture to nanomechanics". Nat. Rev. Mol. Cell Biol. 8 (7): 562–73. doi:10.1038/nrm2197. PMID 17551517.Qin Z, Kreplak L, Buehler MJ (2009). "Hierarchical structure controls nanomechanical properties of vimentin intermediate filaments". PLoS ONE 4 (10): e7294. doi:10.1371/journal.pone.0007294. PMC 2752800. PMID 19806221.Kreplak L, Fudge D (January 2007). "Biomechanical properties of intermediate filaments: from tissues to single filaments and back". Bioessays 29 (1): 26–35. doi:10.1002/bies.20514. PMID 17187357.Qin Z, Buehler MJ, Kreplak L (January 2010). "A multi-scale approach to understand the mechanobiology of intermediate filaments". J Biomech 43 (1): 15–22. doi:10.1016/j.jbiomech.2009.09.004. PMID 19811783.Qin Z, Kreplak L, Buehler MJ (October 2009). "Nanomechanical properties of vimentin intermediate filament dimers". Nanotechnology 20 (42): 425101. doi:10.1088/0957-4484/20/42/425101. PMID 19779230.
- Steinert PM, Chou YH, Prahlad V, Parry DA, Marekov LN, Wu KC, Jang SI, Goldman RD (April 1999). "A high molecular weight intermediate filament-associated protein in BHK-21 cells is nestin, a type VI intermediate filament protein. Limited co-assembly in vitro to form heteropolymers with type III vimentin and type IV alpha-internexin". J. Biol. Chem. 274 (14): 9881–90. doi:10.1074/jbc.274.14.9881. PMID 10092680.
 Further reading
|Wikimedia Commons has media related to: Intermediate filament protein, coiled coil region|
- Intermediate Filament Proteins at the US National Library of Medicine Medical Subject Headings (MeSH)
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Intermediate filament head (DNA binding) region Provide feedback
This family represents the N-terminal head region of intermediate filaments. Intermediate filament heads bind DNA . Vimentin heads are able to alter nuclear architecture and chromatin distribution, and the liberation of heads by HIV-1 protease liberates may play an important role in HIV-1 associated cytopathogenesis and carcinogenesis . Phosphorylation of the head region can affect filament stability . The head has been shown to interaction with the rod domain of the same protein .
Shoeman RL, Huttermann C, Hartig R, Traub P; , Mol Biol Cell 2001;12:143-154.: Amino-terminal polypeptides of vimentin are responsible for the changes in nuclear architecture associated with human immunodeficiency virus type 1 protease activity in tissue culture cells. PUBMED:11160829 EPMC:11160829
Takemura M, Gomi H, Colucci-Guyon E, Itohara S; , J Neurosci 2002;22:6972-6979.: Protective role of phosphorylation in turnover of glial fibrillary acidic protein in mice. PUBMED:12177195 EPMC:12177195
Parry DA, Marekov LN, Steinert PM, Smith TA; , J Struct Biol 2002;137:97-108.: A Role for the 1A and L1 Rod Domain Segments in Head Domain Organization and Function of Intermediate Filaments: Structural Analysis of Trichocyte Keratin. PUBMED:12064937 EPMC:12064937
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR006821
This entry represents the N-terminal head domain of intermediate filaments. Intermediate filament heads bind DNA [PUBMED:11513613]. Vimentin heads are able to alter nuclear architecture and chromatin distribution, and the liberation of heads by HIV-1 protease liberates may play an important role in HIV-1 associated cytopathogenesis and carcinogenesis [PUBMED:11160829]. Phosphorylation of the head region can affect filament stability [PUBMED:12177195]. The head has been shown to interaction with the rod domain of the same protein [PUBMED:12064937].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||intermediate filament (GO:0005882)|
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
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1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
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|Number in seed:||45|
|Number in full:||462|
|Average length of the domain:||84.80 aa|
|Average identity of full alignment:||31 %|
|Average coverage of the sequence by the domain:||16.72 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||9|
|Download:||download the raw HMM for this family|
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This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the More....
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How the sunburst is generated
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Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
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Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.
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The tree shows the occurrence of this domain across different species. More...
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For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
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Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.
We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
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