Content
- Structure
- Assembly
- Features
- Types of intermediate filaments
- Class I and II intermediate filaments: acidic and basic keratins
- Class III of intermediate filaments: Desmin / vimentin type proteins
- Intermediate filament class IV: neurofilament proteins
- Intermediate filament class V: nuclear lamina filaments
- Intermediate filament class VI: Nestinas
- Related pathologies
- References
The intermediate filaments, also known in the literature as “IFs” (from English Intermediate filaments), are a family of insoluble cytosolic fibrous proteins that are present in all cells of multicellular eukaryotes.
They are part of the cytoskeleton, which is an intracellular filamentous network that is mainly responsible for supporting the cell structure and various metabolic and physiological processes such as vesicle transport, cell movement and displacement, etc.
Together with microtubules and microfilaments, intermediate filaments participate in the spatial organization of intracellular organelles, in the processes of endocytosis and exocytosis, and also in the processes of cell division and intercellular communication.
The first intermediate filaments to be studied and described were keratins, one of the first types of proteins whose structure was analyzed by X-ray diffraction in the 1930s.
The concept of intermediate filaments, however, was introduced in the 1980s by Lazarides, who described them as complex "mechanical integrators of the cell space", characterized by their insolubility and their ability to reassemble. in vitro after its denaturation.
Many authors consider them to be the stress "buffer" elements for animal cells, since they are more flexible filaments than microtubules and microfilaments. They are not only found in the cytoskeleton, but they are also part of the nucleoskeleton.
Unlike the other fibrous components of the cytoskeleton, the intermediate filaments do not participate directly in the processes of cell mobility, but rather function in the structural maintenance and mechanical resistance of cells.
Structure
The intermediate filaments have an approximate diameter of 10 nm, a structural characteristic for which they were named, since their size is between the sizes corresponding to myosin and actin filaments, which are between 25 and 7 nm. respectively.
They differ structurally from the other two types of cytoskeletal filaments, which are polymers of globular proteins, in that their constituent units are distinct long-length α-helical fibrous proteins that cluster together to form rope-like structures.
All the proteins that make up the intermediate filaments have a similar molecular organization, consisting of an α-helical or "rope" domain that has different amounts of "coil-forming" segments of the same size.
This helical domain is flanked by an N-terminal non-helical "head" and a non-helical "tail" at the C-terminal end, both of which vary in both size and amino acid sequence.
Within the sequence of these two ends are the consensus motifs that are common for the 6 types of intermediate filaments known.
In vertebrates, the "chord" domain of cytosolic intermediate filament proteins is about 310 amino acid residues, while invertebrate and nuclear lamina cytosolic proteins are roughly 350 amino acids long.
Assembly
Intermediate filaments are "self-assembling" structures that do not possess enzymatic activity, which also differentiates them from their cytoskeletal counterparts (microtubules and microfilaments).
These structures are initially assembled as tetramers of the filamentous proteins that make them up under the influence only of monovalent cations.
These tetramers are 62 nm long and their monomers associate with each other laterally to form "units of length" (UFL). unit-length filaments), known as phase 1 of assembly, which occurs very quickly.
UFLs are the precursors of long filaments and, since the dimers that make them up are joined together in an antiparallel and staggered manner, these units have a central domain with two flanking domains through which phase 2 of elongation occurs. , where the longitudinal union of other UFLs occurs.
During what has been termed as phase 3 of the assembly, radial compaction of the diameter of the filaments occurs, which produces mature intermediate filaments of more or less 10 nm in diameter.
Features
The functions of the intermediate filaments depend considerably on the type of cell considered and, in the case of animals (including humans), their expression is regulated in a tissue-specific way, so it also depends on the type of tissue than in study.
Epithelia, muscles, mesenchymal and glial cells and neurons have different types of filaments, specialized according to the function of the cells to which they belong.
Among these functions, the most important are the structural maintenance of cells and resistance to different mechanical stresses, since these structures have a certain elasticity that allows them to cushion different types of forces imposed on the cells.
Types of intermediate filaments
The proteins that make up the intermediate filaments belong to a large and heterogeneous family of filamentous proteins that are chemically different but that are distinguished into six classes according to their sequence homology (I, II, III, IV, V and VI).
Although it is not very common, different types of cells, under very particular conditions (development, cell transformation, growth, etc.) can co-express more than one class of intermediate filament-forming proteins
Class I and II intermediate filaments: acidic and basic keratins
Keratins account for most of the proteins in the middle filaments and, in humans, they make up more than three-quarters of the middle filaments.
They have molecular weights that vary between 40 and 70 kDa and differ from other intermediate filament proteins by their high content of glycine and serine residues.
They are known as acidic and basic keratins because of their isoelectric points, which are between 4.9 and 5.4 for acidic keratins and between 6.1 and 7.8 for basic ones.
In these two classes, around 30 proteins have been described and are present especially in epithelial cells, where both types of proteins "co-polymerize" and form compound filaments.
Many of the intermediate filament case I keratins are found in structures such as hair, nails, horns, spikes, and claws, while those of class II are the most abundant in the cytosol.
Class III of intermediate filaments: Desmin / vimentin type proteins
Desmin is a 53 kDa acidic protein that, depending on its degree of phosphorylation, has different variants.
Some authors have also called desmin filaments "intermediate muscle filaments", since their presence is quite restricted, although in small quantities, to all types of muscle cells.
In myofibrils, desmin is found in the Z line, so it is thought that this protein contributes to the contractile functions of muscle fibers by functioning at the junction of myofibrils and the plasma membrane.
In turn, vimentin is a protein present in mesenchymal cells. The intermediate filaments formed by this protein are flexible and have been found to resist many of the conformational changes that occur during the cell cycle.
It is found in fibroblasts, smooth muscle cells, white blood cells, and other cells of the circulatory system of animals.
Intermediate filament class IV: neurofilament proteins
Also known as "neurofilaments", this class of intermediate filaments comprises one of the fundamental structural elements of neuronal axons and dendrites; they are often associated with the microtubules that also make up these structures.
The neurofilaments of vertebrate animals have been isolated, determining that it is a triplet of proteins of 200, 150 and 68 kDa that participate in the assembly in vitro.
They differ from other intermediate filaments in that they have lateral arms as "appendages" that project from the periphery thereof and that function in the interaction between neighboring filaments and other structures.
Glial cells produce a special type of intermediate filaments known as glial intermediate filaments, which differ structurally from neurofilaments in that they are composed of a single 51 kDa protein and have different physicochemical properties.
Intermediate filament class V: nuclear lamina filaments
All the laminae that are part of the nucleoskeleton are actually intermediate filament proteins. They are between 60 and 75 kDa molecular weight and are found in the nuclei of all eukaryotic cells.
They are essential for the internal organization of the nuclear regions and for many of the functions of this organelle essential for the existence of eukaryotes.
Intermediate filament class VI: Nestinas
This type of intermediate filament weighs more or less 200 kDa and is predominantly found in stem cells of the central nervous system. They are expressed during neuronal development.
Related pathologies
There are multiple diseases in humans that are related to the intermediate filaments.
In some types of cancer such as malignant melanomas or breast carcinomas, for example, the co-expression of intermediate filaments of vimentin and keratin leads to the differentiation or interconversion of epithelial and mesenchymal cells.
This phenomenon has been experimentally shown to increase the migratory and invasive activity of cancer cells, which has important implications for the metastatic processes characteristic of this condition.
Eriksson et al. (2009) review the different types of diseases and their relationship with specific mutations in the genes involved in the formation of the six types of intermediate filaments.
Diseases related to mutations in the coding genes for the two types of keratin are epidermolysis bullosa, epidermolytic hyperkeratosis, corneal dystrophy, keratoderma, and many others.
Type III intermediate filaments are involved in numerous cardiomyopathies and in different muscular diseases mainly related to dystrophies. In addition, they are also responsible for dominant cataracts and some types of sclerosis.
Many neurological syndromes and disorders are associated with type IV filaments, such as Parkinson's. In the same way, genetic defects in type V and VI filaments are responsible for the development of different autosomal diseases and related to the functioning of the cell nucleus.
Examples of these are Hutchinson-Gilford progeria syndrome, Emery-Dreifuss muscular dystrophy, among others.
References
- Anderton, B. H. (1981). Intermediate filaments: a family of homologous structures. Journal of Muscle Research and Cell Motility, 2(2), 141–166.
- Eriksson, J. E., Pallari, H., Robert, D., Eriksson, J. E., Dechat, T., Grin, B.,… Goldman, R. D. (2009). Introducing intermediate filaments: from discovery to disease. The Journal of Clinical Investigation, 119(7), 1763–1771.
- Fuchs, E., & Weber, K. (1994). Intermediate Filaments: Structure, Dynamics, Function and Disease. Annu. Rev. Biochem., 63, 345–382.
- Hendrix, M. J. C., Seftor, E. A., Chu, Y. W., Trevor, K. T., & Seftor, R. E. B. (1996). Role of intermediate filaments in migration, invasion and metastasis. Cancer and Metastasis Reviews, 15(4), 507–525.
- Herrmann, H., & Aebi, U. (2004). Intermediate Filaments: Molecular Structure, Assembly Mechanism, and Integration into Functionally Distinct Intracellular Scaffolds. Annual Review of Biochemistry, 73(1), 749–789.
- Herrmann, H., & Aebi, U. (2016). Intermediate Filaments: Structure and Assembly. Cold Spring Harbor Perspectives in Biology, 8, 1–22.
- McLean, I., & Lane, B. (1995). Intermediate filaments in disease. Current Opinion in Cell Biology, 7(1), 118–125.
- Steinert, P., & Roop, D. (1988). Molecular and Cellular Biology of Intermediate Filaments. Annual Review of Biochemistry, 57(1), 593–625.
- Steinert, P., Jones, J., & Goldman, R. (1984). Intermediate filaments. The Journal of Cell Biology, 99(1), 1–6.
FAQs
What are the types and functions of intermediate filaments? ›
Two types of intermediate filaments, desmin and the neurofilaments, play specialized roles in muscle and nerve cells, respectively. Desmin connects the individual actin-myosin assemblies of muscle cells both to one another and to the plasma membrane, thereby linking the actions of individual contractile elements.
What is the structure of intermediate filaments? ›Intermediate filaments are composed of smaller strands in the shape of rods. Eight rods are aligned in a staggered array with another eight rods, and these components all twist together to form the rope-like conformation of an intermediate filament.
What are type 3 intermediate filaments? ›There are four proteins classified as type III intermediate filament (IF) proteins: desmin, glial fibrillary acidic protein (GFAP), peripherin, and vimentin. Desmin is expressed in all muscle types, GFAP is expressed in astrocytes and other glial cells, and peripherin is expressed in peripheral neurons.
What are the 5 intermediate filaments? ›The intermediate filaments comprise the major component of the cytoskeleton and consist of five major subgroups—vimentin, keratins, desmin, neurofilaments, and glial fibrillary acidic protein (GFAP)—and a small number of minor subgroups (e.g., nestin, peripherin).
What is the main function of intermediate filaments quizlet? ›Intermediate filaments have great tensile strength, and their main function is to enable cells to withstand the mechanical stress that occurs when cells are stretched.
What is the filament function? ›The main function that filament performs is to carry nutrients to the anther for the development of the anther and pollen grains.
What are two functions of intermediate filaments? ›- Helping cells adhere to other cells, allowing epithelial tissues to resist tension.
- Helping cells adhere to the extracellular matrix.
- Providing structure for internal organelles, such as lamins forming a cage around the nucleus.
The primary function of intermediate filaments is to create cell cohesion and prevent the acute fracture of epithelial cell sheets under tension.
What is the structure and function of microfilaments? ›Microfilaments, also called actin filaments, as they consist of two intertwined strands of a globular protein known as actin. They are the polymers of the protein actin and are smallest filaments of the cytoskeleton. They have a vital role in cell movements, cell division, and muscle contraction.
What are the different types of intermediate filaments? ›The intermediate filaments comprise the major component of the cytoskeleton and consist of five major subgroups—vimentin, keratins, desmin, neurofilaments, and glial fibrillary acidic protein (GFAP)—and a small number of minor subgroups (e.g., nestin, peripherin).
What are the three types of filaments? ›
Three major types of filaments make up the cytoskeleton: actin filaments, microtubules, and intermediate filaments. Actin filaments occur in a cell in the form of meshworks or bundles of parallel fibres; they help determine the shape of the cell and also help it adhere to the substrate.
What are the two types of filaments? ›Most of the cytoplasm consists of myofibrils, which are cylindrical bundles of two types of filaments: thick filaments of myosin (about 15 nm in diameter) and thin filaments of actin (about 7 nm in diameter).
What is the structure of filament? ›Each filament is a twisted chain of identical globular actin molecules, all these molecules point in the same direction along the axis of the chain. Therefore an actin filament has a structural polarity, with a plus and a minus end. Actin filaments are thinner,more flexible, and generally shorter than microtubules.
What best describes an intermediate filament? ›Intermediate filaments, in contrast to actin filaments and microtubules, are very stable structures that form the true skeleton of the cell. They anchor the nucleus and position it within the cell, and they give the cell its elastic properties and its ability to withstand tension.
What are the properties of intermediate filaments? ›IFs have a high tensile strength and are resistant to compression, twisting and bending forces. The elastic nature of intermediate filaments is due the staggered assembly of their subunits into protofilaments and the high degree of lateral versus longitudinal interactions within the filaments.
What are the three functions of microfilaments? ›Microfilaments are the smallest filaments of the cytoskeleton. They have roles in cell movement, muscle contraction, and cell division.
What are the key functions of microfilaments? ›Key Points
Microfilaments assist with cell movement and are made of a protein called actin. Actin works with another protein called myosin to produce muscle movements, cell division, and cytoplasmic streaming. Microfilaments keep organelles in place within the cell.
The functional roles for microfilaments involve cell membrane motility, endo- and exocytosis, secretion and vesicle transfer.
What is a filament made of? ›Traditional filaments are coiled wire (kind of like a spring) that are located inside of the glass bulb. They're typically made from tungsten because of its high melting temperature. Tungsten's predisposition to heat is a key factor in filament bulbs working.
How does the filament break? ›If there are no issues with the filament spool or routing, the filament could be brittle from age, heat, or moisture. If the filament has been stored outside of its packaging, or has been exposed to high humidity over time, it can be subject to breakage.
What is filament example? ›
A filament is a very thin piece or thread of something, for example the piece of wire inside a light bulb.
How do intermediate filaments form? ›Pairs of dimers then associate in an anti-parallel fashion to form staggered tetramers. Lateral associations between eight tetramers form unit-length filaments, which are able to anneal to each other, end-to-end, to form intermediate filaments.
What is the function of intermediate? ›The most important function of rope like arrangement of microtubules intermediate filaments is to provide mechanical support to the plasma membrane where it comes into contact with other cells or with the extracellular matrix. Thus, it provides mechanical stability to the cell.
Are intermediate filaments responsible for movement? ›Intermediate filaments have no role in cell movement. Their function is purely structural. They bear tension, thus maintaining the shape of the cell, and anchor the nucleus and other organelles in place.
What do intermediate filaments regulate? ›Intermediate filaments regulate nucleus rigidity
Thus, alterations of nucleus rigidity affect the cell ability to squeeze in between matrix fibers. Lamins are the type IV intermediate filament proteins that are the major components of the nuclear membrane [50] and largely affect the mechanical property of the nucleus.
Intermediate filaments are found in animal cells, where they form a net that spreads from the nuclear envelope to the plasma membrane (Figure 1). They are usually anchored to adhesion cell complexes such as desmosomes, hemidesmosomes and focal adhesions.
What is the function of microtubules and microfilaments? ›Microtubules are important for establishing and maintaining growth directionality and focus, whereas microfilaments are required for delivering material to the actual growth sites.
What are the types of filaments normally used? ›There are three types of filaments: microtubules, microfilaments (known as actin filaments), and intermediate filaments. Together, these three types of filaments make up the cytoskeleton.
What is the function of intermediate filaments in cytoskeleton? ›Intermediate filaments (IFs) are a key component of the cytoskeleton in virtually all vertebrate cells, including those of the lens of the eye. IFs help integrate individual cells into their respective tissues.
Why are intermediate filaments called that? ›Initially designated 'intermediate' because their average diameter (10 nm) is between those of narrower microfilaments (actin) and wider myosin filaments found in muscle cells, the diameter of intermediate filaments is now commonly compared to actin microfilaments (7 nm) and microtubules (25 nm).
How many filaments are there? ›
Currently we offer 8 standard filaments which are Engineering PLA, ABS filament , PETG filament , NYLON , a carbon fibre filament composite, PVA, HIPS , Flexible filament (TPU) and Polypropylene.
What is called filament? ›noun. fil·a·ment ˈfil-ə-mənt. : a single thread or a thin flexible threadlike object, process, or appendage. especially : an elongated thin series of cells attached one to another or a very long thin cylindrical single cell (as of some algae, fungi, or bacteria) filamentous.
How are filaments formed? ›Filament formation by Gln1 is a highly cooperative process, strongly dependent on macromolecular crowding, and involves back-to-back stacking of cylindrical homo-decamers into filaments that associate laterally to form higher order fibrils. Other metabolic enzymes also assemble into filaments at low pH.
What are filament types? ›| Filament | Special Properties | Durability |
|---|---|---|
| PLA | Easy to print Biodegradable, though only in very specific conditions | Medium |
| ABS | Durable Impact resistant | High |
| PETG (XT, N‑Vent) | More flexible than PLA or ABS Durable | High |
| Nylon | Strong Flexible Durable | High |
Typical 3D printing filament types used include PLA, PETG, or ABS. For the purpose of comparison, ABS-filled 3D printer plastic will be used. Carbon-fiber-filled filaments have improved mechanical properties when compared to unfilled thermoplastics. They also have good dimensional stability.
What is the size of a filament? ›Filament Diameter
Most 3D printer filament comes in one of two standard diameter sizes: 1.75mm or 2.85mm (often referred to as 3.0mm). The size you use depends on the printer you use. Most printers use either one or the other.
- Helping cells adhere to other cells, allowing epithelial tissues to resist tension.
- Helping cells adhere to the extracellular matrix.
- Providing structure for internal organelles, such as lamins forming a cage around the nucleus.
The eukaryotic cytoskeleton is composed primarily of three types of filaments: microfilaments, intermediate filaments, and microtubules. Microfilaments are composed of linear actin polymers. Intermediate filaments are composed of a variety of different proteins. Microtubules are hollow structures composed of tubulin.
What are 2 Functions of microfilaments? ›In association with myosin, microfilaments help to generate the forces used in cellular contraction and basic cell movements. The filaments also enable a dividing cell to pinch off into two cells and are involved in amoeboid movements of certain types of cells.
What are the two main filaments? ›Most of the cytoplasm consists of myofibrils, which are cylindrical bundles of two types of filaments: thick filaments of myosin (about 15 nm in diameter) and thin filaments of actin (about 7 nm in diameter).
What are examples of intermediate filaments? ›
The intermediate filaments comprise the major component of the cytoskeleton and consist of five major subgroups—vimentin, keratins, desmin, neurofilaments, and glial fibrillary acidic protein (GFAP)—and a small number of minor subgroups (e.g., nestin, peripherin).
What are the 2 types of protein filament? ›The myofilaments are of two types: thick filaments composed of the protein myosin, and thin filaments composed mainly of the protein actin but with a complex of two other proteins, troponin and tropomyosin, closely associated with it.
What is an example of filament? ›The stamen of a flower — the part that produces pollen — consists of a slender stalk, called a filament and an anther. The filament supports the anther, which is where pollen develops. The word filament is from the Latin word filum, which means "thread." Filament, in fact, can be a synonym for thread.
What is the structure of a filament? ›Each filament is a twisted chain of identical globular actin molecules, all these molecules point in the same direction along the axis of the chain. Therefore an actin filament has a structural polarity, with a plus and a minus end. Actin filaments are thinner,more flexible, and generally shorter than microtubules.
What are the 3 functions of the cytoskeletal filaments? ›The fundamental functions of the cytoskeleton are involved in modulating the shape of the cell, providing mechanical strength and integrity, enabling the movement of cells and facilitating the intracellular transport of supramolecular structures, vesicles and even organelles.
What are the functions of microfilaments intermediate filaments and microtubules? ›1: Microfilaments thicken the cortex around the inner edge of a cell; like rubber bands, they resist tension. Microtubules are found in the interior of the cell where they maintain cell shape by resisting compressive forces. Intermediate filaments are found throughout the cell and hold organelles in place.
What is the function of intermediate filaments in smooth muscle cells? ›Intermediate filaments coordinate focal adhesion assembly/disassembly, contraction, and nucleus rigidity. The vimentin intermediate filament network undergoes phosphorylation and spatial reorganization in smooth muscle, which regulates its function in smooth muscle.