Plastin is part of a family of

actin Actin is a protein family, family of Globular protein, globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in myofibril, muscle fibrils. It is found in essentially all Eukaryote, eukaryotic cel ...

-bundling

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

s, specifically the

α-actinin Actinin is a microfilament protein. Alpha-actinin-1 is necessary for the attachment of actin myofilaments to the Z-lines in skeletal muscle cells, and to the dense bodies in smooth muscle cells. The functional protein is an anti-parallel dimer ...

family of actin-binding protein, which are found in many

lifeforms Life form (also spelled life-form or lifeform) is an entity that is living, such as plants (flora) and animals (fauna). It is estimated that more than 99% of all species that ever existed on Earth, amounting to over five billion species, are ex ...

, from

humans Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

and other

animals Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

plants Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

and

yeasts Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...

. These proteins are known to

cross-link In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...

actin filaments into bundles for various cell purposes.Members of plastin include: * LCP1 * PLS1 * PLS3

Structure

The structure of plastin has been evolutionarily maintained within organisms who utilize this protein, which includes humans and lower eukaryotic organisms. Plastin structures are known for their

EF-hand The EF hand is a helix–loop–helix structural domain or ''motif'' found in a large family of calcium-binding proteins. The EF-hand motif contains a helix–loop–helix topology, much like the spread thumb and forefinger of the human hand, in ...

Ca²⁺- and actin-binding domains that assist in assembling actin into higher-order bundles. Plastins have two actin-binding domains (ABD) in each of their polypeptide in which each ABD contains two of 125-residue calponin-homology (CH) components. This structure allows for plastins to cross-link actin filaments into their bundles in order to perform various tasks.

Function

Plastin, along with other actin-binding proteins, help stabilize and rearrange organization of actin cytoskeleton when present with external stimuli, cell migration, and cell adhesion. The EF-hand Ca²⁺-binding domains are important for the function of plastin as their activities are regulated by Ca²⁺. In mammals, three isoforms of plastin have been identified: L-plastin, found mostly within hematopoietic cells; T-plastin, found in cells of solid tissues; and lastly, I-plastin, expressed specifically in the small intestine, colon, and kidneys. Each of these isoforms of plastin have their own roles, dependent of the cell-type, in order to regulate the actin cytoskeleton.

L-plastin

L-plastin (leukocyte plastin, LPL, Plastin-2, LCP1), are expressed in

hematopoietic Haematopoiesis (, from Greek , 'blood' and 'to make'; also hematopoiesis in American English; sometimes also h(a)emopoiesis) is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells ...

cells and in various types of

leukocytes White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mul ...

(i.e., T- and B-lymphocytes). They help to defend against foreign pathogens by using

phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis i ...

. They help contribute to the motility of T-cells so that these cells are capable of activating during an immune response. L-plastins are known to be the only isoform within the three to undergo

phosphorylation In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, ...

during leukocyte activation via interleukin-1, -2, and phorbol myristate acetate. This, and the fact that plastins are Ca²⁺-dependent, allow L-plastins to be capable of signaling to leukocytes for rapid responses to stimuli. As a result, organisms or cells that are lacking L-plastins have a more difficult time responding to external stimuli that need an immunity activation.

T-Plastin

Also written PLS3 or Plastin-3, T-plastins are primarily found in solid tissues, within cells that are capable of replication (i.e.,

epithelial Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellu ...

and

mesenchymal Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every ...

cells). T-plastins are needed in order for cells to carry out proliferation and migration as well as membranes to protrude from cell to another cell and gap the distance within the

extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide struc ...

(ECM). These proteins strengthen the actin-cytoskeleton network to accomplish cell migration and distribution. Without T-plastin, cells who migrate using the protrusion method would not be able to bypass the membrane tension that needs to be overcome in order for protrusion to occur.

I-Plastin

I-plastin (intestinal plastin, plastin-1, PLS1) is localized to the intestinal epithelial cells, specifically in the intestinal

brush border A brush border (striated border or brush border membrane) is the microvilli-covered surface of simple cuboidal and simple columnar epithelium found in different parts of the body. Microvilli are approximately 100 nanometers in diameter and their ...

microvilli Microvilli (singular: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, and are involved in a wide variety of functions, including absorption, secretion, ...

. I-plastin help to stabilize the intestinal brush border microvilli and its function. Without I-plastin, it has been observed that there was decreased transepithelial resistance, increased cellular turnover, and increased sensitivity to specific diseases in the intestines. Phenotypically, microvilli in the intestines lacking this protein were found to be shorter, constricted, not have profound rootlets, and have increased fragility.

References

{{Reflist EF-hand-containing proteins Protein families Human proteins