G-Actin (PDB code: 1j6z). ADP and the divalent cation are highlighted.

F-Actin; surface representation of 13 subunit repeat based on Ken Holmes' actin filament model

Actin is a globular, roughly 42-kDa protein found in all eukaryotic cells (except for nematode sperm) where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans. It is the monomeric subunit of microfilaments, one of the three major components of the cytoskeleton, and of thin filaments, which are part of the contractile apparatus in muscle cells. Thus, actin participates in many important cellular functions, including muscle contraction, cell motility, cell division and cytokinesis, vesicle and organelle movement, cell signaling, and the establishment and maintenance of cell junctions and cell shape. Image File history File links Download high resolution version (762x675, 640 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Actin PyMOL ... Image File history File links Download high resolution version (762x675, 640 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Actin PyMOL ... For the file format that describes the 3D structures of molecules found in the Protein Data Bank, see Protein Data Bank (file format). ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... Image File history File links Download high resolution version (1073x291, 346 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Actin ... Image File history File links Download high resolution version (1073x291, 346 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Actin ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Classes Adenophorea    Subclass Enoplia    Subclass Chromadoria Secernentea    Subclass Rhabditia    Subclass Spiruria    Subclass Diplogasteria    Subclass Tylenchia The nematodes or roundworms (Phylum nematoda from Greek (nema): thread + -ode like) are one of the most common phyla of animals, with over 80,000 different described species (over 15,000 are parasitic). ... Conservation is a high degree of similarity in the primary or higher structure of homologous proteins amongst various phyla. ... For other uses, see Species (disambiguation). ... For the programming language, see algae (programming language). ... This article is about modern humans. ... A monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer [1]. // Examples of monomers are hydrocarbons such as the alkene and arene homologous series. ... This article or section should be merged with actin Microfilaments or actin filaments are made up of two twisted monomeric actin subunits. ... The eukaryotic cytoskeleton. ... Motility is a biological term which refers to the ability to move spontaneously and independently. ... A cell that has almost completed cytokinesis. ... Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. ... A cell junction is a structure within a tissue of a multicellular organism. ...

Formation of thin filament

Formation of thin filament

Genetics

Principal interactions of structural proteins at cadherin-based adherens junction. Actin filaments are linked to α-actinin and to membrane through vinculin. The head domain of vinculin associates to E-cadherin via α-, β-, and γ-catenins. The tail domain of vinculin binds to membrane lipids and to actin filaments. Image File history File links Adherens_Junctions_structural_proteins. ... Image File history File links Adherens_Junctions_structural_proteins. ... Cadherins are a class of proteins which are expressed on the surface of cells. ... The adherent culture of BPAE cells featured in the digital image above was immunofluorescently labeled with primary anti-vinculin mouse monoclonal antibodies followed by goat anti-mouse Fab heavy and light chain fragments conjugated to Rhodamine Red-X. (www. ...

The protein actin is one of the most highly conserved throughout evolution because it interacts with a large number of other proteins, with 80.2% sequence conservation at the gene level between Homo sapiens and Saccharomyces cerevisiae (a species of yeast), and 95% conservation of the primary structure of the protein product. Conservation is a high degree of similarity in the primary or higher structure of homologous proteins amongst various phyla. ... For other uses, see Gene (disambiguation). ... This article is about modern humans. ... Binomial name Meyen ex E.C. Hansen Saccharomyces cerevisiae is a species of budding yeast. ... A protein primary structure is a chain of amino acids. ...

Although most yeasts have only a single actin gene, higher eukaryotes, in general, express several isoforms of actin encoded by a family of related genes. Mammals have at least six actin isoforms coded by separate genes,^[1] which are divided into three classes (alpha, beta and gamma) according to their isoelectric point. In general, alpha actins are found in muscle (α-skeletal, α-aortic smooth, α-cardiac, and γ2-enteric smooth), whereas beta and gamma isoforms are prominent in non-muscle cells (β- and γ1-cytoplasmic). Although the amino acid sequences and in vitro properties of the isoforms are highly similar, these isoforms cannot completely substitute for one another in vivo.^[2] Typical divisions Ascomycota (sac fungi) Saccharomycotina (true yeasts) Taphrinomycotina Schizosaccharomycetes (fission yeasts) Basidiomycota (club fungi) Urediniomycetes Sporidiales Yeasts are a growth form of eukaryotic micro organisms classified in the kingdom Fungi, with about 1,500 species described;[1] they dominate fungal diversity in the oceans. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the... 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. ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria For the folk-rock band see The Mammals. ... The isoelectric point (pI) is the pH at which a molecule or surface carries no net electrical charge. ... In vitro (Latin: within the glass) refers to the technique of performing a given experiment in a test tube, or, generally, in a controlled environment outside a living organism. ... In vivo (Latin for (with)in the living). ...

The typical actin gene has an approximately 100-nucleotide 5' UTR, a 1200-nucleotide translated region, and a 200-nucleotide 3' UTR. The majority of actin genes are interrupted by introns, with up to 6 introns in any of 19 well-characterised locations. The high conservation of the family makes actin the favoured model for studies comparing the introns-early and introns-late models of intron evolution. In eukaryotic genetics, the 5 UTR (read as 5 prime UnTranslated Region) is a particular section of messenger RNA (mRNA). ... Translation is the second process of protein biosynthesis (part of the overall process of gene expression). ... In genetics, the 3 UTR (read as 3 prime untranslated region) is a particular section of messenger RNA (mRNA). ... Diagram of the location of introns and exons within a gene. ...

All non-spherical prokaryotes appear to possess genes such as MreB, which encode homologues of actin; these genes are required for the cell's shape to be maintained. The plasmid-derived gene ParM encodes an actin-like protein whose polymerised form is dynamically unstable, and appears to partition the plasmid DNA into the daughter cells during cell division by a mechanism analogous to that employed by microtubules in eukaryotic mitosis.^[3] Actin is found in both smooth and rough endoplasmic reticulums. Prokaryotic bacteria cell structure Prokaryotes (IPA: //) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. ... MreB is a protein found in bacteria that has been identified as a homologue of actin. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ... Figure 1: Illustration of a bacterium with plasmids enclosed showing chromosomal DNA and plasmids. ... Microtubules are one of the components of the cytoskeleton. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Mitosis divides genetic information during cell division. ...

Functions

Actin has three main functions in cells :

• To form the most dynamic one of the three subclasses of the cytoskeleton, which gives mechanical support to cells, and hardwires the cytoplasm with the surroundings to support signal transduction.
• To allow cell motility (see Actoclampin molecular motors).
• In muscle cells as well as non-muscle cells, to generate force together with myosin proteins to support muscle contraction, vesicle movement, and other transport processes.

The eukaryotic cytoskeleton. ... Motility is a biological term which refers to the ability to move spontaneously and independently. ... This article or section should be merged with actin Microfilaments or actin filaments are made up of two twisted monomeric actin subunits. ... For other uses of Muscle, see Muscle (disambiguation). ... Myosin is a motor protein filament found in muscle tissue. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ...

Microfilaments

Individual subunits of actin are known as globular actin (G-actin). G-actin subunits assemble into long filamentous polymers called F-actin. Two parallel F-actin strands twist around each other in a helical formation, giving rise to microfilaments of the cytoskeleton. Microfilaments measure approximately 7 nm in diameter with a loop of the helix repeating every 37 nm. This article or section should be merged with actin Microfilaments or actin filaments are made up of two twisted monomeric actin subunits. ... In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles (or coassembles) with other protein molecules to form a multimeric or oligomeric protein. ... 3-dimensional structure of hemoglobin, a globular protein. ... Biopolymers are a class of polymers produced by living organisms. ... A nanometre (American spelling: nanometer) is 1. ... DIAMETER is a computer networking protocol for AAA (Authentication, Authorization and Accounting). ...

Polarity

The polarity of an actin filament can be determined by decorating the microfilament with myosin "S1" fragments, creating barbed (+) and pointed (-) ends on the filament. An S1 fragment is composed of the head and neck domains of myosin II. Myosin is a motor protein filament found in muscle tissue. ...

Actomyosin filaments

In muscle, actin is the major component of thin filaments, which, together with the motor protein myosin (which forms thick filaments), are arranged into actomyosin myofibrils. These fibrils comprise the mechanism of muscle contraction. Using the hydrolysis of ATP for energy, myosin heads undergo a cycle during which they attach to thin filaments, exerting a tension, and then depending on the load, perform a power stroke that causes the thin filaments to slide past, shortening the muscle. For other uses of Muscle, see Muscle (disambiguation). ... This is a list of gene families or gene complexes, that is sets of genes which occur across a number of different species which often serve similar biological functions. ... Myosin is a motor protein filament found in muscle tissue. ... A diagram of the structure of a Myofybril Myofibrils (obsolete term: sarcostyles) are cylindrical organelles, found within muscle cells. ... A top-down view of skeletal muscle A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ...

In contractile bundles, the actin-bundling protein alpha-actinin separates each thin filament by ~35 nm. This increase in distance allows thick filaments to fit in between and interact, enabling deformation or contraction. In deformation, one end of myosin is bound to the plasma membrane while the other end "walks" toward the plus end of the actin filament. This pulls the membrane into a different shape relative to the cell cortex. For contraction, the myosin molecule is usually bound to two separate filaments and both ends simultaneously "walk" toward their filament's plus end, sliding the actin filaments closer to each other. This results in the shortening, or contraction, of the actin bundle (but not the filament). This mechanism is responsible for muscle contraction and cytokinesis, the division of one cell into two. Actinin is a microfilament protein. ... 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. ... A cell cortex is made of actin microfilaments. ... A cell that has almost completed cytokinesis. ...

Actin polymerization and depolymerization is necessary in chemotaxis and cytokinesis. Nucleating factors are necessary to stimulate actin polymerization. Also, Actin filaments themselves bind ATP, and hydrolysis of this ATP stimulates destabilization of the polymer. Chemotaxis is a kind of taxis, in which bodily cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. ... A cell that has almost completed cytokinesis. ...

History

Actin was first observed experimentally in 1887 by W.D. Halliburton, who extracted a protein from muscle that 'coagulated' preparations of myosin, and that he dubbed "myosin-ferment."^[4] However, Halliburton was unable to further characterise his findings, and the discovery of actin is credited instead to Brúnó F. Straub, a young biochemist working in Albert Szent-Györgyi's laboratory at the Institute of Medical Chemistry at the University of Szeged, Hungary. In the scientific method, an experiment (Latin: ex- periri, of (or from) trying) is a set of observations performed in the context of solving a particular problem or question, to retain or falsify a hypothesis or research concerning phenomena. ... Year 1887 (MDCCCLXXXVII) was a common year starting on Saturday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Thursday of the 12-day slower Julian calendar). ... Albert Szent-Györgyi at the time of his appointment to the National Institutes of Health Albert Szent-Györgyi de Nagyrápolt (September 16, 1893 – October 22, 1986) was a Hungarian physiologist who won the Nobel Prize in Physiology or Medicine in 1937. ... Central building of the University of Szeged at Dugonics Square The University of Szeged is one of the most distinguished universities in Hungary and in Central Europe. ...

In 1942, Straub developed a novel technique for extracting muscle protein that allowed him to isolate substantial amounts of relatively-pure actin. Straub's method is essentially the same as that used in laboratories today. Szent-Gyorgyi had previously described the more viscous form of myosin produced by slow muscle extractions as 'activated' myosin, and, since Straub's protein produced the activating effect, it was dubbed actin. The hostilities of World War II meant that Szent-Gyorgyi and Straub were unable to publish the work in Western scientific journals; it became well-known in the West only in 1945, when it was published as a supplement to the Acta Physiologica Scandinavica.^[5] Year 1942 (MCMXLII) was a common year starting on Thursday (the link will display the full 1942 calendar) of the Gregorian calendar. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... For alternative meanings for The West in the United States, see the U.S. West and American West. ... Nature, Science and PNAS In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. ... Year 1945 (MCMXLV) was a common year starting on Monday (link will display the full calendar). ...

Straub continued to work on actin and in 1950 reported that actin contains bound ATP ^[6] and that, during polymerisation of the protein into microfilaments, the nucleotide is hydrolysed to ADP and inorganic phosphate (which remain bound in the microfilament). Straub suggested that the transformation of ATP-bound actin to ADP-bound actin played a role in muscular contraction. In fact, this is true only in smooth muscle, and was not supported through experimentation until 2001.^[7] Year 1950 (MCML) was a common year starting on Sunday (link will display the full calendar) of the Gregorian calendar. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... A nucleotide is a chemical compound that consists of 3 portions: a heterocyclic base, a sugar, and one or more phosphate groups. ... Adenosine diphosphate, abbreviated ADP, is a nucleotide. ... A phosphate, in inorganic chemistry, is a salt of phosphoric acid. ... Smooth muscle Layers of Esophageal Wall: 1. ... This article is about the year. ...

The crystal structure of G-actin was solved in 1990 by Kabsch and colleagues.^[8] In the same year a model for F-actin was proposed by Holmes and colleagues.^[9] The model was derived by fitting a helix of G-actin structures according to low-resolution fiber diffraction data from the filament. Several models of the filament have been proposed since. However there is still no high-resolution X-ray structure of F-actin. X-ray crystallography, also known as single-crystal X-ray diffraction, is the oldest and most common crystallographic method for determining the structure of molecules. ... This article is about the year. ...

The Listeria bacteria use the cellular machinery to move around inside the host cell, by inducing directed polymerisation of actin by the ActA transmembrane protein, thus pushing the bacterial cell around. Species Listeria monocytogenes Listeria ivanovii Listeria innocua Listeria welshimeri Listeria seegligeri Listeria grayi Listeria innocua Listeria is a bacterial genus containing six species. ... A transmembrane protein is a protein that spans the entire biological membrane. ...

See also

• MreB - an actin homologue in bacteria
• Motor protein
• ACTA1 - alpha actin 1
• ACTB - beta actin
• ACTG1 - gamma actin 1

MreB is a protein found in bacteria that has been identified as a homologue of actin. ... This is a list of gene families or gene complexes, that is sets of genes which occur across a number of different species which often serve similar biological functions. ...

References