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In molecular biology, the cupin superfamily of proteins is a diverse superfamily of proteins containing a conserved barrel domain, with ''cupa'' being the Latin term for a small barrel. The cupin protein superfamily includes a wide variety of enzymes, but notably contains the non-enzymatic seed storage proteins also. The cupin superfamily plays a role in allergy, specifically the 11 S globulins (found in legumins) and the 7S members (found in vicilins). These can be found as seed storage proteins and may be a component of normal human diet. ''Sclerotinia sclerotiorum'' (Lib.) deBary was the first oxalic acid (oxalate), secreting organism to be described as early as 1886 in Botan. Z. by A. de Barry. However, since oxalate secreting fungi are not a major threat to crop cereals no studies of this interaction were made for almost 100 years. In the early 1980s a protein dubbed 'germin' was identified in germinating wheat embryos; and in the early 1990s (1992) it was found to be an enzyme having oxalate oxidase (OXO) activity converting an oxalate substrate into carbon dioxide and hydrogen peroxide. ''S. sclerotiorum'', better known as "white mold", is a fungal disease of many economically valuable crops such as (legumes) beans, soybeans, peanuts, etc., potato, lettuce, sunflower. 400 plant species are susceptible including stone fruits....〔http://www.broadinstitute.org/annotation/genome/sclerotinia_sclerotiorum/MultiHome.html〕〔https://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/WhiteMold.aspx〕 Thomas Burr Osborne (chemist) at the end of the 19th century was the first person to systematically study seed storage proteins by their solubility characteristics. He established 4 classes of proteins: water-soluble albumins; salt soluble globulins: vicilin—typically having sedimentation coefficients, S values (a measure of the protein mass determined by sedimentation equilibrium ultracentrifugation) of about 7 Svedberg units (hence the common name 7S globulin) and legumin (11S); alcohol/water-soluble—cereal—prolamines; and a fourth class, glutelins, of difficultly soluble proteins no longer recognized and now considered low solubility prolamin or globulin storage proteins . Gluten consists of a mixture of prolamins: 'glutenin' and 'gliadin'. Osborne and his Yale colleague Lafayette Mendel are considered the 'founders' of the modern science of nutrition. Legumin and vicilin share a common evolutionary ancestor, namely, a vicilin-like protein in a fern-spore which also exhibits some characteristics of legumin. Each of these proteins contains equivalent 'subunits' indicating an evolution from a single-gene ancestor which has been duplicated during evolution. It was suggested that "germin" , a plant enzyme, oxalate oxidase___ 'one-very-tough-little- protein' ___ as such an ancestor. This hypothesis stimulated a search for the evolutionary roots of the seed storage globulins which include such food proteins as the legume soy protein—the gold standard for plant-based proteins—due to its balanced content of 7S and 11S globulin protein, other beans, the pseudocereals buckwheat, & quinoa, pumpkin seeds, cocoa, coffee, nuts, and the two cereals oats and rice.... This search turned up a new realm: that seed storage globulin proteins (7S & 11S), as well as many other non-storage plant proteins and microbial proteins belong to a vast superfamily of proteins dubbed the 'cupin superfamily' of proteins, named on the basis of a conserved beta-barrel fold , originally discovered within germin and germin-like proteins from higher plants. Germin is a monocupin and 7S & 11S are each bicupins. It is a large and functionally immensely diverse 'superfamily' of proteins, numbering in the thousands, that have a common origin and whose evolution can be followed from bacteria to eukaryotes including animals and higher plants. "Cupins" are the most functionally diverse protein superfamily occurring in all spermatophytes (seed bearing plants). " GLPs, moreover, are now known to be ubiquitous plant proteins, no longer linked only to cereal germination, but involved in plant responses to biotic and abiotic stress.〔http://www.ingentaconnect.com/content/tandf/bpts/2008/00000027/00000005/art00002〕"G-OXOs and GLPs are plant do-all proteins." Germin of the "true cereals" is known as the 'archetypal' member of the cupin superfamily, however it is not to be considered an empty cask or barrel but a 'jellyroll' in which six monomer subunits are wrapped in three dimensions to form a barrel shape. This structure accounts for its astonishing 'refractory' nature toward various 'denaturing' agents: all germins share a remarkable stability when subjected to heat, detergents, extreme pH and resistance to broad specificity proteolytic (digestive) enzymes. Ironically, seed storage proteins of grasses and cereals belong to the eponymous prolamin superfamily which also includes plant albumins(2S). Prolamin seed storage proteins so characteristic of cereals and grasses is not considered very nutritious because of its high content of the amino acid proline which it shares with gelatin and its low content of lysine, a vital amino acid. Germin was initially identified in the early stages of wheat seed germination, thus its name. Interestingly, domesticated cereals most notably 'hexaploid' bread wheat ( pasta wheat is tetraploid) was selected by humans for its resistance to fungal pathogens. Many years later it was found to have oxalate oxidase activity generating 'antimicrobial' hydrogen peroxide from a substrate of the double-acid, oxalic acid, secreted by an invading fungus or other microbe. A reaction between oxalate and the calcium cation makes calcium oxalate, a type of 'kidney stone' in humans. Amazingly, oxalate is a metabolite of ascorbate (vitamin C), and it is worth emphasizing that ascorbate is a direct precursor of oxalate in plants. The 'sweetest' outcome from our knowledge of germin biochemistry is that the wheat-germin gene is the obvious candidate for insertion into the American chestnut for producing a transgenic American chestnut. This tree called the "perfect tree" has no resistance to Cryphonectria parasitica, the chestnut blight fungus.〔http://www.susanfreinkel.com/books_American_Chestnut.html〕 The fungal mycelium produce oxalic acid which eats away at the tree's bark giving it a portal into the underlying growing tissue. The xylem vessels carrying water become plugged through the chelation of calcium cations by oxalate just as in the kidney. Death is by strangulation as a canker encircles and girdles the trunk. Transgenic American chestnut seedlings have been produced and field tested carrying the wheat germin gene for oxalate oxidase which breaks down oxalic acid the caustic chemical excreted by the invasive chestnut blight fungus. Soybean Protein Nomenclature: Aprogress naldc.nal.usda.gov/download/31396/PDF 1. Effects of ionic strength on the ultracentrifuge pattern for water-extractable soybean proteins at pH 7.6. The terminology used most extensively in the past. == References == 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cupin superfamily」の詳細全文を読む スポンサード リンク
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