Actin

alpha-actinF-actinthin filamentactin cytoskeletonActin filaments(G-actin)actin fibersactin microfilamentsactinsmicrofilament protein
Actin is a family of globular multi-functional proteins that form microfilaments.wikipedia
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Muscle

musclesmuscularmusculature
An actin protein is the monomeric subunit of two types of filaments in cells: microfilaments, one of the three major components of the cytoskeleton, and thin filaments, part of the contractile apparatus in muscle cells. Actin therefore contributes to processes such as the intracellular transport of vesicles and organelles as well as muscular contraction and cellular migration.
Muscle cells contain protein filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and the shape of the cell.

Protein

proteinsprotein synthesisproteinaceous
Actin is a family of globular multi-functional proteins that form microfilaments.
Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape.

Microfilament

actin filamentsmicrofilamentsactin filament
An actin protein is the monomeric subunit of two types of filaments in cells: microfilaments, one of the three major components of the cytoskeleton, and thin filaments, part of the contractile apparatus in muscle cells. Actin is a family of globular multi-functional proteins that form microfilaments. Straub continued to work on actin, and in 1950 reported that actin contains bound ATP and that, during polymerization of the protein into microfilaments, the nucleotide is hydrolyzed to ADP and inorganic phosphate (which remain bound to the microfilament).
Microfilaments, also called actin filaments, are filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton and are primarily composed of polymers of actin, but in cells are modified by and interact with numerous other proteins.

Cytoskeleton

cytoskeletalcytoskeletal proteinsactin cytoskeleton
An actin protein is the monomeric subunit of two types of filaments in cells: microfilaments, one of the three major components of the cytoskeleton, and thin filaments, part of the contractile apparatus in muscle cells.
During contraction of a muscle, within each muscle cell, myosin molecular motors collectively exert forces on parallel actin filaments.

Signal transduction

signaling pathwayssignaling cascadesignal transduction pathways
A cell's ability to dynamically form microfilaments provides the scaffolding that allows it to rapidly remodel itself in response to its environment or to the organism's internal signals, for example, to increase cell membrane absorption or increase cell adhesion in order to form cell tissue.
Such signaling is mainly orchestrated in focal adhesions, regions where the integrin-bound actin cytoskeleton detects changes and transmits them downstream through YAP1.

Cell (biology)

cellcellscellular
It can be present as either a free monomer called G-actin (globular) or as part of a linear polymer microfilament called F-actin (filamentous), both of which are essential for such important cellular functions as the mobility and contraction of cells during cell division.
The subunit protein of microfilaments is a small, monomeric protein called actin.

Heart

cardiachuman heartapex of the heart
Mutations in the different genes that regulate actin production in humans can cause muscular diseases, variations in the size and function of the heart as well as deafness.
These are mostly associated with muscle contraction, and bind with actin, myosin, tropomyosin, and troponin.

MreB

In addition to the similarities that exist between an organism's isoforms there is also an evolutionary conservation in the structure and function even between organisms contained in different eukaryotic domains: in bacteria the actin homologue MreB has been identified, which is a protein that is capable of polymerizing into microfilaments; and in archaea the homologue Ta0583 is even more similar to the eukaryotic actins.
MreB is a protein found in bacteria that has been identified as a homologue of actin, as indicated by similarities in tertiary structure and conservation of active site peptide sequence.

Protein–protein interaction

interactprotein-protein interactionprotein-protein interactions
In addition, it is able to carry out more interactions than any other protein, which allows it to perform a wider variety of functions than other proteins at almost every level of cellular life.
Myosin filaments act as molecular motors and by binding to actin enables filament sliding.

ACTG1

G actingammagamma-actin
In vertebrates, three main groups of actin isoforms, alpha, beta, and gamma have been identified.
Gamma-actin is eventually replaced by sarcomeric alpha-actin isoforms, with low levels of gamma-actin persisting in adult myocytes which associate with Z-disc and costamere domains.

Cell junction

intercellular junctionsjunctional complexcell junctions
Actin participates in many important cellular processes, 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.

Nematode

Nematodanematodesroundworm
It is found in essentially all eukaryotic cells (the only known exception being nematode sperm), where it may be present at a concentration of over 100 μM; its mass is roughly 42-kDa, with a diameter of 4 to 7 nm.
Nematode sperm is thought to be the only eukaryotic cell without the globular protein G-actin.

Muscle contraction

contractionmuscular contractionexcitation-contraction coupling
An actin protein is the monomeric subunit of two types of filaments in cells: microfilaments, one of the three major components of the cytoskeleton, and thin filaments, part of the contractile apparatus in muscle cells.
The binding of ATP to a myosin head detaches myosin from actin, thereby allowing myosin to bind to another actin molecule.

Myosin

myosin IImyosin heavy chainmyosins
Actin was first observed experimentally in 1887 by W.D. Halliburton, who extracted a protein from muscle that 'coagulated' preparations of myosin that he called "myosin-ferment".
They are ATP-dependent and responsible for actin-based motility.

Tropomyosin

t'''ropomyosin
The helical F-actin filament found in muscles also contains a tropomyosin molecule, which is a 40 nanometre long protein that is wrapped around the F-actin helix.
These structures are collectively known as the cytoskeleton, and one of the most ancient systems is based on filamentous polymers of the protein actin.

Brunó Ferenc Straub

Brunó F. StraubBrunó Ferenc'' ''Straub
However, Halliburton was unable to further refine his findings, and the discovery of actin is credited instead to Brunó Ferenc Straub, a young biochemist working in Albert Szent-Györgyi's laboratory at the Institute of Medical Chemistry at the University of Szeged, Hungary.
As a young scholar he was a research assistant of Albert Szent-Györgyi at the University of Szeged, and subsequently worked at the Molteno Institute, Cambridge, UK. He is credited with the discovery of actin.

Cofilin

ADF/cofilinADF (actin-depolymerizing factor)/cofilin family
Some proteins, such as cofilin appear to increase the angle of turn, but again this could be interpreted as the establishment of different structural states.
ADF/cofilin is a family of actin-binding proteins which disassembles actin filaments.

Gene expression

expressionexpressedexpress
Lastly, actin plays an important role in the control of gene expression.
A housekeeping gene is a gene that is required to maintain basic cellular function and so is typically expressed in all cell types of an organism. Examples include actin, GAPDH and ubiquitin. Some housekeeping genes are transcribed at a relatively constant rate and these genes can be used as a reference point in experiments to measure the expression rates of other genes.

Troponin I

There are other protein molecules bound to the tropomyosin thread, these are the troponins that have three polymers: troponin I, troponin T and troponin C.
Troponin I is a part of the troponin protein complex, where it binds to actin in thin myofilaments to hold the actin-tropomyosin complex in place.

Adenosine diphosphate

ADPadenosine diphosphate (ADP)adenosine diphosphate sugars
Straub continued to work on actin, and in 1950 reported that actin contains bound ATP and that, during polymerization of the protein into microfilaments, the nucleotide is hydrolyzed to ADP and inorganic phosphate (which remain bound to the microfilament).
For example, the transfer of energy from ATP to the protein myosin causes a conformational change when connecting to actin during muscle contraction.

Tubulin

β-tubulinγ-tubulinα-tubulin
It was initially thought that it only bound with actin and tubulin, although recent immunoprecipitation studies have shown that it interacts with a large number of polypeptides, which possibly function as substrates.
Both α and β tubulins have a mass of around 50 kDa and are thus in a similar range compared to actin (with a mass of ~42 kDa).

Troponin

troponin complexcardiac troponinstroponin test
There are other protein molecules bound to the tropomyosin thread, these are the troponins that have three polymers: troponin I, troponin T and troponin C.
Troponin is attached to the protein tropomyosin and lies within the groove between actin filaments in muscle tissue.

Albert Szent-Györgyi

Albert von Szent-Györgyi NagyrapoltAlbert Szent-GyörgyAlbert Szent-Györgyi von Nagyrapolt
However, Halliburton was unable to further refine his findings, and the discovery of actin is credited instead to Brunó Ferenc Straub, a young biochemist working in Albert Szent-Györgyi's laboratory at the Institute of Medical Chemistry at the University of Szeged, Hungary.
He found that muscles contain actin, which when combined with the protein myosin and the energy source ATP, contract muscle fibers.

Vinculin

VCL
Actin filaments are linked to α-actinin and to the membrane through vinculin.
In mammalian cells, vinculin is a membrane-cytoskeletal protein in focal adhesion plaques that is involved in linkage of integrin adhesion molecules to the actin cytoskeleton.

Cell migration

migrationcell motilitycellular migration
Actin therefore contributes to processes such as the intracellular transport of vesicles and organelles as well as muscular contraction and cellular migration.
Experimentation has shown that there is rapid actin polymerisation at the cell's front edge.