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Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm and have an inner diameter between 11 and 15 nm. They are formed by the polymerization of a dimer of two globular proteins, alpha and beta tubulin into protofilaments that can then associate laterally to form a hollow tube, the microtubule. The most common form of a microtubule consists of 13 protofilaments in the tubular arrangement.
A flagellum is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
Keratin is one of a family of structural fibrous proteins also known as scleroproteins. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, and the outer layer of skin among vertebrates. Keratin also protects epithelial cells from damage or stress. Keratin is extremely insoluble in water and organic solvents. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals. Excessive keratinization participate in fortification of certain tissues such as in horns of cattle and rhinos, and armadillos' osteoderm. The only other biological matter known to approximate the toughness of keratinized tissue is chitin. Keratin comes in two types, the primitive, softer forms found in all vertebrates and harder, derived forms found only among sauropsids.
The evolution of flagella is of great interest to biologists because the three known varieties of flagella – each represent a sophisticated cellular structure that requires the interaction of many different systems.
The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. It is composed of three main components, microfilaments, intermediate filaments and microtubules, and these are all capable of rapid growth or disassembly dependent on the cell's requirements.
Intermediate filaments (IFs) are cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate Branchiostoma.
Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytoskeleton. Microtubules function in many essential cellular processes, including mitosis. Tubulin-binding drugs kill cancerous cells by inhibiting microtubule dynamics, which are required for DNA segregation and therefore cell division.
Cytokeratins are keratin proteins found in the intracytoplasmic cytoskeleton of epithelial tissue. They are an important component of intermediate filaments, which help cells resist mechanical stress. Expression of these cytokeratins within epithelial cells is largely specific to particular organs or tissues. Thus they are used clinically to identify the cell of origin of various human tumors.
Internexin, alpha-internexin, is a Class IV intermediate filament approximately 66 KDa. The protein was originally purified from rat optic nerve and spinal cord. The protein copurifies with other neurofilament subunits, as it was originally discovered, however in some mature neurons it can be the only neurofilament expressed. The protein is present in developing neuroblasts and in the central nervous system of adults. The protein is a major component of the intermediate filament network in small interneurons and cerebellar granule cells, where it is present in the parallel fibers.
Peripherin is a type III intermediate filament protein expressed mainly in neurons of the peripheral nervous system. It is also found in neurons of the central nervous system that have projections toward peripheral structures, such as spinal motor neurons. Its size, structure, and sequence/location of protein motifs is similar to other type III intermediate filament proteins such as desmin, vimentin and glial fibrillary acidic protein. Like these proteins, peripherin can self-assemble to form homopolymeric filamentous networks, but it can also heteropolymerize with neurofilaments in several neuronal types. This protein in humans is encoded by the PRPH gene. Peripherin is thought to play a role in neurite elongation during development and axonal regeneration after injury, but its exact function is unknown. It is also associated with some of the major neuropathologies that characterize amyotropic lateral sclerosis (ALS), but despite extensive research into how neurofilaments and peripherin contribute to ALS, their role in this disease is still unidentified.
Neurofilaments (NF) are classed as type IV intermediate filaments found in the cytoplasm of neurons. They are protein polymers measuring 10 nm in diameter and many micrometers in length. Together with microtubules (~25 nm) and microfilaments (7 nm), they form the neuronal cytoskeleton. They are believed to function primarily to provide structural support for axons and to regulate axon diameter, which influences nerve conduction velocity. The proteins that form neurofilaments are members of the intermediate filament protein family, which is divided into six types based on their gene organization and protein structure. Types I and II are the keratins which are expressed in epithelia. Type III contains the proteins vimentin, desmin, peripherin and glial fibrillary acidic protein (GFAP). Type IV consists of the neurofilament proteins L, M, H and internexin. Type V consists of the nuclear lamins, and type VI consists of the protein nestin. The type IV intermediate filament genes all share two unique introns not found in other intermediate filament gene sequences, suggesting a common evolutionary origin from one primitive type IV gene.
An axoneme, also called an axial filament is the microtubule-based cytoskeletal structure that forms the core of a cilium or flagellum. Cilia and flagella are found on many cells, organisms, and microorganisms, to provide motility. The axoneme serves as the "skeleton" of these organelles, both giving support to the structure and, in some cases, the ability to bend. Though distinctions of function and length may be made between cilia and flagella, the internal structure of the axoneme is common to both.
In cell biology, microtubule-associated proteins (MAPs) are proteins that interact with the microtubules of the cellular cytoskeleton. MAPs are integral to the stability of the cell and its internal structures and the transport of components within the cell.
Crescentin is a protein which is a bacterial relative of the intermediate filaments found in eukaryotic cells. Just as tubulins and actins, the other major cytoskeletal proteins, have prokaryotic homologs in, respectively, the FtsZ and MreB proteins, intermediate filaments are linked to the crescentin protein. Some of its homologs are erroneously labelled Chromosome segregation protein ParA. This protein family is found in Caulobacter and Methylobacterium.
Major sperm protein (MSP) is a nematode specific small protein of 126 amino acids with a molecular weight of 14 kDa. It is the key player in the motility machinery of nematodes that propels the crawling movement/motility of nematode sperm. It is the most abundant protein present in nematode sperm, comprising 15% of the total protein and more than 40% of the soluble protein. MSP is exclusively synthesized in spermatocytes of the nematodes. The MSP has two main functions in the reproduction of the helminthes: i) as cytosolic component it is responsible for the crawling movement of the mature sperm, and ii) once released, it acts as hormone on the female germ cells, where it triggers oocyte maturation and stimulates the oviduct wall to contract to bring the oocytes into position for fertilization. MSP has first been identified in Caenorhabditis elegans.
In biology, a protein filament is a long chain of protein monomers, such as those found in hair, muscle, or in flagella. Protein filaments form together to make the cytoskeleton of the cell. They are often bundled together to provide support, strength, and rigidity to the cell. When the filaments are packed up together, they are able to form three different cellular parts. The three major classes of protein filaments that make up the cytoskeleton include: actin filaments, microtubules and intermediate filaments.
Microtubule-associated protein 2 is a protein in humans that is encoded by the MAP2 gene.
The prokaryotic cytoskeleton is the collective name for all structural filaments in prokaryotes. It was once thought that prokaryotic cells did not possess cytoskeletons, but advances in visualization technology and structure determination led to the discovery of filaments in these cells in the early 1990s. Not only have analogues for all major cytoskeletal proteins in eukaryotes been found in prokaryotes, cytoskeletal proteins with no known eukaryotic homologues have also been discovered. Cytoskeletal elements play essential roles in cell division, protection, shape determination, and polarity determination in various prokaryotes.
In enzymology, an alpha-tubulin N-acetyltransferase is an enzyme which is encoded by the ATAT1 gene.
Tektin-1 is a protein that in humans is encoded by the TEKT1 gene.
References
- ↑ MA Pirner and RW Linck; Tektins are heterodimeric polymers in flagellar microtubules with axial periodicities matching the tubulin lattice; J. Biol. Chem., Vol. 269, Issue 50, 31800-31806, Dec, 1994
- ↑ Setter PW, Malvey-Dorn E, Steffen W, Stephens RE, Linck RW (September 2006). "Tektin interactions and a model for molecular functions". Exp. Cell Res. 312 (15): 2880–96. doi:10.1016/j.yexcr.2006.05.014. PMID 16831421.
- ↑ Norrander JM, Amos LA, Linck RW (September 1992). "Primary structure of tektin A1: comparison with intermediate-filament proteins and a model for its association with tubulin". Proc. Natl. Acad. Sci. U.S.A. 89 (18): 8567–71. Bibcode:1992PNAS...89.8567N. doi: 10.1073/pnas.89.18.8567 . PMC 49961 . PMID 1528862.
- 1 2 3 Amos LA, Norrander JM, Perrone CA, Linck RW (1996). "Structural comparison of tektins and evidence for their determination of complex spacings in flagellar microtubules". J. Mol. Biol. 257 (2): 385–397. doi:10.1006/jmbi.1996.0170. PMID 8609631.
- ↑ Iguchi N, Tanaka H, Nakamura Y, Nozaki M, Fujiwara T, Nishimune Y (June 2002). "Cloning and characterization of the human tektin-t gene". Mol. Hum. Reprod. 8 (6): 525–30. doi: 10.1093/molehr/8.6.525 . PMID 12029069.
- ↑ Larsson M, Norrander J, Gräslund S, Brundell E, Linck R, Ståhl S, Höög C (October 2000). "The spatial and temporal expression of Tekt1, a mouse tektin C homologue, during spermatogenesis suggest that it is involved in the development of the sperm tail basal body and axoneme". Eur. J. Cell Biol. 79 (10): 718–25. doi:10.1078/0171-9335-00097. PMID 11089920.
- ↑ Whinnett A, Brower AVZ, Lee M-M, Willmott KR, Mallet J (June 2005). "Phylogenetic Utility of Tektin, a Novel Region for Inferring Systematic Relationships Among Lepidoptera". Annals of the Entomological Society of America. 98 (6): 873–886. doi:10.1603/0013-8746(2005)098[0873:PUOTAN]2.0.CO;2.