Endopolygalacturonase I | |||||||
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Identifiers | |||||||
Organism | |||||||
Symbol | pgaI | ||||||
UniProt | P26213 | ||||||
Other data | |||||||
EC number | 3.2.1.15 | ||||||
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Pectinases are a group of enzymes that breaks down pectin, a polysaccharide found in plant cell walls, through hydrolysis, transelimination and deesterification reactions. [1] [2] Commonly referred to as pectic enzymes, they include pectolyase, pectozyme, and polygalacturonase, one of the most studied and widely used[ citation needed ] commercial pectinases. It is useful because pectin is the jelly-like matrix which helps cement plant cells together and in which other cell wall components, such as cellulose fibrils, are embedded. Therefore, pectinase enzymes are commonly used in processes involving the degradation of plant materials, such as speeding up the extraction of fruit juice from fruit, including apples and sapota. Pectinases have also been used in wine production since the 1960s. [3] The function of pectinase in brewing is twofold, first it helps break down the plant (typically fruit) material and so helps the extraction of flavors from the mash. Secondly the presence of pectin in finished wine causes a haze or slight cloudiness. Pectinase is used to break this down and so clear the wine.
Pectinases can be extracted from fungi such as Aspergillus niger . The fungus produces these enzymes to break down the middle lamella in plants so that it can extract nutrients from the plant tissues and insert fungal hyphae. If pectinase is boiled it is denatured (unfolded) making it harder to connect with the pectin at the active site, and produce as much juice.
Pectinase enzymes used today are naturally produced by fungi and yeasts (50%), insects, bacteria and microbes (35%) and various plants (15%), [4] but cannot be synthesized by animal or human cells. [5] In plants, pectinase enzymes hydrolyze pectin that is found in the cell wall, allowing for new growth and changes to be made. Similarly to their role in plants, pectinases break down pectin during the developmental stage of fungi.
Pectinase enzymes are classified based on how their enzymatic reaction proceeds with various pectic substances (through transelimination or hydrolysis), the preferred substrate (pectin, pectic acid or oligo-n-galacturonate) and if the cleavage that occurs is random or end-wise. [6] [1]
Pectinases depolymerise pectin through hydrolysis, trans-elimination and deesterification reaction processes, breaking down the ester bond that holds together the carboxyl and methyl groups in pectin. [6]
Endo-polygalacturonase progresses through a reaction along the following pathway: [7]
(1,4-alpha-D-galacturonosyl)n+m + H2O = (1,4-alpha-D-galacturonosyl)n + (1,4-alpha-D-galacturonosyl)m
All pectinase enzyme structures include a prism-shaped right-handed cylinder made up of seven to nine parallel β-helices. The three parallel β-helices that create the prism shape of the structure are referred to as PB1, PB2 and PB3, with PB1 and PB2 creating an antiparallel β and PB3 sitting perpendicularly to PB2. All substrate binding sites of the various esterases, hydrolases, and lyases are located on an outer cleft of the central parallel β-helix structure between protruding loops on the structure and PB1. [8]
As with all enzymes, pectinases have an optimum temperature and pH at which they are most active. For example, a commercial pectinase might typically be activated at 45 to 55 °C and work well at a pH of 3.0 to 6.5. [3]
Pectinase enzymes play various roles in both the fruit juice and wine industries. They are used for clarification in fruit juices and also speed up fruit juice extraction through enzymatic liquefaction of fruit pulp. In addition, pectinase enzymes aid in formation of pulpy products in the fruit juice industry. Pectinase enzymes are used for extracting juice from purée. This is done when the enzyme pectinase breaks down the substrate pectin and the juice is extracted. The enzyme pectinase lowers the activation energy needed for the juice to be produced and catalyzes the reaction.
Pectinases are useful in the wine industry by extracting anthocyanin from the fruit, effectively intensifying the wine coloring. [6] Pectinase can also be used to extract juices from cell walls of plants cells.
Pectinases are also used for retting in the textile industry. [9] Addition of chelating agents or pretreatment of the plant material with acid enhance the effect of the enzyme.
A cell wall is a structural layer that surrounds some cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, and functions as a selective barrier. Another vital role of the cell wall is to help the cell withstand osmotic pressure and mechanical stress. While absent in many eukaryotes, including animals, cell walls are prevalent in other organisms such as fungi, algae and plants, and are commonly found in most prokaryotes, with the exception of mollicute bacteria.
Orange juice is a liquid extract of the orange tree fruit, produced by squeezing or reaming oranges. It comes in several different varieties, including blood orange, navel oranges, valencia orange, clementine, and tangerine. As well as variations in oranges used, some varieties include differing amounts of juice vesicles, known as "pulp" in American English, and "(juicy) bits" in British English. These vesicles contain the juice of the orange and can be left in or removed during the manufacturing process. How juicy these vesicles are depend upon many factors, such as species, variety, and season. In American English, the beverage name is often abbreviated as "OJ".
An amylase is an enzyme that catalyses the hydrolysis of starch into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion. Foods that contain large amounts of starch but little sugar, such as rice and potatoes, may acquire a slightly sweet taste as they are chewed because amylase degrades some of their starch into sugar. The pancreas and salivary gland make amylase to hydrolyse dietary starch into disaccharides and trisaccharides which are converted by other enzymes to glucose to supply the body with energy. Plants and some bacteria also produce amylase. Specific amylase proteins are designated by different Greek letters. All amylases are glycoside hydrolases and act on α-1,4-glycosidic bonds.
Pectin is a heteropolysaccharide, a structural polymer contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal chemical component of pectin is galacturonic acid which was isolated and described by Henri Braconnot in 1825. Commercially produced pectin is a white-to-light-brown powder, produced from citrus fruits for use as an edible gelling agent, especially in jams and jellies, dessert fillings, medications, and sweets; as a food stabiliser in fruit juices and milk drinks, and as a source of dietary fiber.
Cellulase is any of several enzymes produced chiefly by fungi, bacteria, and protozoans that catalyze cellulolysis, the decomposition of cellulose and of some related polysaccharides:
An exoenzyme, or extracellular enzyme, is an enzyme that is secreted by a cell and functions outside that cell. Exoenzymes are produced by both prokaryotic and eukaryotic cells and have been shown to be a crucial component of many biological processes. Most often these enzymes are involved in the breakdown of larger macromolecules. The breakdown of these larger macromolecules is critical for allowing their constituents to pass through the cell membrane and enter into the cell. For humans and other complex organisms, this process is best characterized by the digestive system which breaks down solid food via exoenzymes. The small molecules, generated by the exoenzyme activity, enter into cells and are utilized for various cellular functions. Bacteria and fungi also produce exoenzymes to digest nutrients in their environment, and these organisms can be used to conduct laboratory assays to identify the presence and function of such exoenzymes. Some pathogenic species also use exoenzymes as virulence factors to assist in the spread of these disease-causing microorganisms. In addition to the integral roles in biological systems, different classes of microbial exoenzymes have been used by humans since pre-historic times for such diverse purposes as food production, biofuels, textile production and in the paper industry. Another important role that microbial exoenzymes serve is in the natural ecology and bioremediation of terrestrial and marine environments.
Pectic acid, also known as polygalacturonic acid, is a water-soluble, transparent gelatinous acid existing in over-ripe fruit and some vegetables. It is a product of pectin degradation in plants, and is produced via the interaction between pectinase and pectin In the early stage of development of fruits, the pectic substance is a water-insoluble protopectin which is converted into pectin by the enzyme protopectinase during ripening of fruit. In over-ripe fruits, due to the presence of pectic methyl esterase enzyme, the pectin gets largely converted to pectic acid which is water-insoluble. Due to this reason both immature and over-ripe fruits are not suitable for making jelly and only ripe fruits are used.
Finings are substances that are usually added at or near the completion of the processing of making wine, beer, and various nonalcoholic juice beverages. They are used to remove compounds, either to improve clarity or adjust flavor or aroma. The removed compounds may be sulfides, proteins, polyphenols, benzenoids, or copper ions. Unless they form a stable sediment in the final container, the spent finings are usually discarded from the beverage along with the target compounds that they capture.
Saprobionts are organisms that digest their food externally and then absorb the products. This process is called saprotrophic nutrition. Fungi are examples of saprobiontic organisms, which are a type of decomposer.
Endo-1,4-β-xylanase is any of a class of enzymes that degrade the linear polysaccharide xylan into xylose, thus breaking down hemicellulose, one of the major components of plant cell walls:
β-Amylase is an enzyme with the systematic name 4-α-D-glucan maltohydrolase. It catalyses the following reaction:
β-Glucosidase is an enzyme that catalyses the following reaction:
Pectinesterase (EC 3.1.1.11; systematic name pectin pectylhydrolase) is a ubiquitous cell-wall-associated enzyme that presents several isoforms that facilitate plant cell wall modification and subsequent breakdown. It catalyzes the following reaction:
Pectate lyase is an enzyme involved in the maceration and soft rotting of plant tissue. Pectate lyase is responsible for the eliminative cleavage of pectate, yielding oligosaccharides with 4-deoxy-α-D-mann-4-enuronosyl groups at their non-reducing ends. The protein is maximally expressed late in pollen development. It has been suggested that the pollen expression of pectate lyase genes might relate to a requirement for pectin degradation during pollen tube growth.
Pectin lyase is a polysaccharide enzyme with a complex structure that is present in plant cell walls. It has a significant role in pectin degradation and different biotechnological and industrial applications. It can be found in many different organisms.
Rhamnogalacturonan-II (RG-II) is a complex polysaccharide component of pectin that is found in the primary cell walls of dicotyledonous and monocotyledonous plants and gymnosperms. It is supposed to be crucial for the plant cell wall integrity. RG-II is also likely to be present in the walls of some lower plants. Its global structure is conserved across vascular plants, albeit a number of variations within the RGII side chains have been observed between different plants. RG-II is composed of 12 different glycosyl residues including D-rhamnose, D-apiose, D-galactose, L-galactose, Kdo, D-galacturonic acid, L-arabinose, D-xylose, and L-aceric acid, linked together by at least 21 distinct glycosidic linkages. Some resides are further modified via methylation and acetylation. It moreover supports borate mediated cross-linking between different RGII side-chain apiosyl residues. The backbone consists of a linear polymer of alpha-1,4-linked D-galactopyranosiduronic acid. RG-II can be isolated from different sources, such as apple juice and red wine.
Endo-polygalacturonase (EC 3.2.1.15, pectin depolymerase, pectolase, pectin hydrolase, and poly-α-1,4-galacturonide glycanohydrolase; systematic name (1→4)-α-D-galacturonan glycanohydrolase (endo-cleaving)) is an enzyme that hydrolyzes the α-1,4 glycosidic bonds between galacturonic acid residues:
Polygalacturonase inhibitor proteins (PGIPs), also known as polygalacturonase-inhibiting proteins, are plant proteins capable of inhibiting the action of polygalacturonase (PG) enzymes produced by bacterial and fungal pathogens. PGs can be produced by pathogens to degrade the polygalacturonan component of plant cell walls. PGIPs are leucine-rich repeat glycoproteins of approximately 360 amino acids in length, and PGIPs may reduce the activity of PGs by one or two orders of magnitude. Both competitive and non-competitive inhibition has been observed for various PGIPs. However, no inhibition of endogenous plant PGs that participate in fruit ripening by PGIPs have been reported.
In molecular biology, glycoside hydrolase family 28 is a family of glycoside hydrolases EC 3.2.1., which are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycoside hydrolases, based on sequence similarity, has led to the definition of >100 different families. This classification is available on the CAZy web site, and also discussed at CAZypedia, an online encyclopedia of carbohydrate active enzymes.
Glucanases are enzymes that break down large polysaccharides via hydrolysis. The product of the hydrolysis reaction is called a glucan, a linear polysaccharide made of up to 1200 glucose monomers, held together with glycosidic bonds. Glucans are abundant in the endosperm cell walls of cereals such as barley, rye, sorghum, rice, and wheat. Glucanases are also referred to as lichenases, hydrolases, glycosidases, glycosyl hydrolases, and/or laminarinases. Many types of glucanases share similar amino acid sequences but vastly different substrates. Of the known endo-glucanases, 1,3-1,4-β-glucanase is considered the most active.