Intermediate filaments (IFs) are important structural proteins which are located both in the cytoplasm and the nucleus. Intermediate filaments have a diameter between that of actin (microfilaments) and microtubules. IFs crisscross the cytosol from the nuclear envelope to the cell membrane. G-Actin (PDB code: 1j6z). ... This article or section should be merged with actin Microfilaments or actin filaments are made up of two twisted monomeric actin subunits. ... Microtubules are protein structures found within cells, one of the components of the cytoskeleton. ... ÃThe cytosol (as opposed fatty cytoplasm, which also includes the organelles) is the internal fluid of the cell, and a large part of cell metabolism occurs here. ... The nuclear envelope refers to the double membrane of the nucleus that encloses genetic material in eukaryotic cells. ... Drawing of a cell membrane A cell membrane, plasma membrane or plasmalemma is a selectively permeable lipid bilayer coated by proteins which comprises the outer layer of a cell. ...

Structure

The domain structure of IF molecules is conserved. Each protein has a non-alpha-helical (globular) domain at the N and C-termini which surrounds the alpha-helical rod domain. 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 which then assemble into longer structures. Side view of an α-helix of alanine residues in atomic detail. ... Sucrose, or common table sugar, is composed of glucose and fructose. ... A coiled coil is a structural motif found in many proteins. ...

The anti-parallel orientation of tetramers means that, unlike microtubules and microfilaments which have a plus end and a minus end, IFs lack polarity.

Cytoplasmic IF do not undergo treadmilling like microtubules and actin fibers, but they are dynamic. For a review see: [1]. This article or section does not cite its references or sources. ...

Types

There are about 70 different genes coding for various intermediate filament proteins. However, different kinds of IFs share basic characteristics: they are all polymers that generally measure between 9-11 nm in diameter when fully assembled.

IF are subcatagorized into five types based on similarities in amino acid sequence and protein structure. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

Types I and II - Acidic and Basic Keratins

keratin intermediate filaments

These proteins are the most diverse among IFs and constitute type I (acidic) and type II (basic) IF proteins. The many isoforms are divided in two groups: Fluorescence microscopy of keratin intermediate filaments in epithelial cells. ... Fluorescence microscopy of keratin intermediate filaments in epithelial cells. ... Categories: Cell biology stubs | Keratins ... Type I cytokeratin is a type of cytokeratin, a keratin. ... Type II cytokeratins consist of basic or neutral proteins which are arranged in pairs of heterotypic keratin chains coexpressed during differentiation of simple and stratified epithelial tissues. ... In biology, a protein isoform is a version of a protein with some small differences, usually a splice variant or the product of some posttranslational modification. ...

• 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. In zootomy, epithelium is a tissue composed of a layer of cells. ... Hair keratin is a type of keratin found in hair and nails. ... Young Girl Fixing her Hair, by Sophie Gengembre Anderson Hair is a filamentous outgrowth of dead cells from the skin, found mainly in mammals. ... Nails: left hand, adult human male Anatomy In anatomy, a nail is a horn-like piece at the end of an animal finger or toe. ... Highland cow, a very old long-horned breed from Scotland. ... Orders Procolophonia (extinct) Testudines Araeoscelidia (extinct) Avicephala (extinct) Younginiformes (extinct) Sauropterygia Ichthyosauria (extinct) Placodontia (extinct) Nothosauria (extinct) Plesiosauria (extinct) Sphenodontia Squamata Prolacertiformes (extinct) Archosauria Crurotarsi Order Aetosauria Order Phytosauria Order Rauisuchia Order Crocodilia Ornithodira Pterosauria (extinct) Marasuchus (extinct) Dinosauria (extinct) Order Saurischia Order Ornithischia Reptiles are tetrapods and amniotes, animals... In most biological nomenclature, a scale (Greek lepid, Latin squama) is a small rigid plate that grows out of an animals skin to provide protection. ...

Type III

There are four proteins classed as type III IF proteins which may form homo- or heteropolymeric proteins. A homopolymer is a polymer which is formed from only one type of monomer. ... A heteropolymer, also called a copolymer, is a polymer formed when two (or more) different types of monomer are linked in the same polymer chain, as opposed to a homopolymer where only one monomer is used. ...

• 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 and keep some organelles in a fixed place within the cytoplasm.

Intermediate filaments are one component of the cytoskeleton - important structural components of living cells. ... Image of sarcomere A sarcomere is the basic unit of a cross striated muscles myofibril. ... Intermediate filaments are one component of the cytoskeleton - important structural components of living cells. ... Astrocytes, also known as astroglia, are characteristic star-shaped glial cells in the brain. ... Neuroglia cells of the brain shown by Golgis method. ... Intermediate filaments are one component of the cytoskeleton - important structural components of living cells. ... Introduction Vimentin is part of the intermediate filament family. ... A fibroblast is a cell that makes the structural fibers and ground substance of connective tissue. ... White Blood Cells is also the name of a White Stripes album. ... The endothelium is the layer of thin, flat cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. ... Schematic of typical animal cell, showing subcellular components. ... Organelles. ...

Type IV

• α-Internexin
• Nestin
• Neurofilaments - the type IV family of intermediate filaments that is found in high concentrations along the axons of vertebrate neurons.
• Synemin
• Syncoilin

Intermediate filaments are one component of the cytoskeleton - important structural components of living cells. ... Nestin is a type IV intermediate filament (IF) protein. ... Intermediate filaments are one component of the cytoskeleton - important structural components of living cells. ... An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ...

Type V - Nuclear Lamins

In metazoan cells there are A and B type lamins which differ in their length and pI. Human cells have three differentially regulated genes. The isoelectric point sucks (pI) is the pH at which a molecule carries no net electrical charge. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ...

• 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". 1 - blastula, 2 - gastrula; orange - ectoderm, red - endoderm. ... The eukaryotic cell nucleus. ... The nuclear lamina is the dense, fibrillar network composed of intermediate filaments made of lamin that lines the inner surface of the nuclear envelope. ... The nuclear envelope refers to the double membrane of the nucleus that encloses genetic material in eukaryotic cells. ...

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 sequence (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 envleope.

Cell adhesion

At the plasma membrane, some keratins interact with desmosomes (cell-cell adhesion) and hemidesmosomes (cell-matrix adhesion) via adapter proteins. Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Cell adhesion in desmosomes A desmosome (also known as macula adherens (Latin for adhering spot ) is a cell structure specialized for cell-to-cell adhesion. ... Hemidesmosomes (HD) are very small stud- or rivet-like structures on the inner basal surface of keratinocytes in the epidermis of skin. ...

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. Filaggrins are filament-associated proteins which bind to keratin fibers in epidermal cells. ... A giant protein (c500 kDa) which binds actin, microtubules and intermediate filaments. ... Myosin is a motor protein filament found in muscle tissue. ...

Keratin filaments in epithelial cells link to desmosomes through plakoglobin, desmoplakin, desmogleins and desmocollins; desmin filaments are connected in a similar way in heart muscle cells. Cell adhesion in desmosomes A desmosome (also known as macula adherens (Latin for adhering spot ) is a cell structure specialized for cell-to-cell adhesion. ... Plakoglobin is a protein associated with desmosomes. ... Cell adhesion in desmosomes Desmoplakin is a protein associated with desmosomes. ... The desmogleins are a family of cadherins consisting of proteins DSG1, DSG2, DSG3, and DSG4. ... Intermediate filaments are one component of the cytoskeleton - important structural components of living 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.

Epidermolysis bullosa simplex (EBS) is a disorder resulting from mutations in the genes encoding keratin 5 or 14. ... Progeria is an extremely rare genetic condition which causes physical changes that resemble greatly accelerated aging in sufferers. ...