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Hydrolysis is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
A glycosidic bond or glycosidic linkage is a type of ether bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.
Glycosylation is the reaction in which a carbohydrate, i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule in order to form a glycoconjugate. In biology, glycosylation usually refers to an enzyme-catalysed reaction, whereas glycation may refer to a non-enzymatic reaction.
Hemagglutinin esterase (HEs) is a glycoprotein that certain enveloped viruses possess and use as an invading mechanism. HEs helps in the attachment and destruction of certain sialic acid receptors that are found on the host cell surface. Viruses that possess HEs include influenza C virus, toroviruses, and coronaviruses of the subgenus Embecovirus. HEs is a dimer transmembrane protein consisting of two monomers, each monomer is made of three domains. The three domains are: membrane fusion, esterase, and receptor binding domains.
Glycosyltransferases are enzymes that establish natural glycosidic linkages. They catalyze the transfer of saccharide moieties from an activated nucleotide sugar to a nucleophilic glycosyl acceptor molecule, the nucleophile of which can be oxygen- carbon-, nitrogen-, or sulfur-based.
The term glycosynthase refers to a class of proteins that have been engineered to catalyze the formation of a glycosidic bond. Glycosynthase are derived from glycosidase enzymes, which catalyze the hydrolysis of glycosidic bonds. They were traditionally formed from retaining glycosidase by mutating the active site nucleophilic amino acid to a small non-nucleophilic amino acid. More modern approaches use directed evolution to screen for amino acid substitutions that enhance glycosynthase activity.
In biochemistry, glycoside hydrolases are a class of enzymes which catalyze the hydrolysis of glycosidic bonds in complex sugars. They are extremely common enzymes, with roles in nature including degradation of biomass such as cellulose (cellulase), hemicellulose, and starch (amylase), in anti-bacterial defense strategies, in pathogenesis mechanisms and in normal cellular function. Together with glycosyltransferases, glycosidases form the major catalytic machinery for the synthesis and breakage of glycosidic bonds.
Exoglycosidases are glycoside hydrolase enzymes that cleave the glycosidic linkage of a terminal monosaccharide in an oligosaccharide or polysaccharide. Because each residue is removed separately, a series of exoglycosidases, each one cleaving at a specific glycolic linkage, is needed. These exoglycosidases can be used to remove a terminal sugar residue, to determine the sequence of a glycan, or for modifying glycans on glycoproteins.
Dispersin B is a 40 kDa glycoside hydrolase produced by the periodontal pathogen, Aggregatibacter actinomycetemcomitans. The bacteria secrete Dispersin B to release adherent cells from a mature biofilm colony by disrupting biofilm formation. The enzyme catalyzes the hydrolysis of linear polymers of N-acetyl-D-glucosamines found in the biofilm matrices. Poly-acetyl glucosamines are integral to the structural integrity of the biofilms of various Gram-positive bacteria and Gram-negative bacteria and are referred to as PIA (PNAG,PS/A) in Staphylococcus species and PGA in Escherichia coli. By degrading the biofilm matrix, Dispersin B allows for the release of bacterial cells that can adhere to new surfaces close by and extend the biofilm or start new colonies. Currently there is interest in Dispersin B as a commercial anti-biofilm agent that could be combined with antibiotics for the treatment of bacterial infections.
A chemical glycosylation reaction involves the coupling of a glycosyl donor, to a glycosyl acceptor forming a glycoside. If both the donor and acceptor are sugars, then the product is an oligosaccharide. The reaction requires activation with a suitable activating reagent. The reactions often result in a mixture of products due to the creation of a new stereogenic centre at the anomeric position of the glycosyl donor. The formation of a glycosidic linkage allows for the synthesis of complex polysaccharides which may play important roles in biological processes and pathogenesis and therefore having synthetic analogs of these molecules allows for further studies with respect to their biological importance.
Oligosaccharides and polysaccharides are an important class of polymeric carbohydrates found in virtually all living entities. Their structural features make their nomenclature challenging and their roles in living systems make their nomenclature important.
The armed/disarmed approach to glycosylation is an effective way to prevent sugar molecules from self-glycosylation when synthesizing disaccharides. This approach was first recognized when acetylated sugars only acted as glycosyl acceptors when reacted with benzylated sugars. The acetylated sugars were termed “disarmed” while the benzylated sugars were termed “armed”.
A glycosyl acceptor is any suitable nucleophile-containing molecule that will react with a glycosyl donor to form a new glycosidic bond. By convention, the acceptor is the member of this pair which did not contain the resulting anomeric carbon of the new glycosidic bond. Since the nucleophilic atom of the acceptor is typically an oxygen atom, this can be remembered using the mnemonic of the acceptor is the alcohol. A glycosyl acceptor can be a mono- or oligosaccharide that contains an available nucleophile, such as an unprotected hydroxyl.
An oxocarbeniumion is a chemical species characterized by a central sp2-hybridized carbon, an oxygen substituent, and an overall positive charge that is delocalized between the central carbon and oxygen atoms. An oxocarbenium ion is represented by two limiting resonance structures, one in the form of a carbenium ion with the positive charge on carbon and the other in the form of an oxonium species with the formal charge on oxygen. As a resonance hybrid, the true structure falls between the two. Compared to neutral carbonyl compounds like ketones or esters, the carbenium ion form is a larger contributor to the structure. They are common reactive intermediates in the hydrolysis of glycosidic bonds, and are a commonly used strategy for chemical glycosylation. These ions have since been proposed as reactive intermediates in a wide range of chemical transformations, and have been utilized in the total synthesis of several natural products. In addition, they commonly appear in mechanisms of enzyme-catalyzed biosynthesis and hydrolysis of carbohydrates in nature. Anthocyanins are natural flavylium dyes, which are stabilized oxocarbenium compounds. Anthocyanins are responsible for the colors of a wide variety of common flowers such as pansies and edible plants such as eggplant and blueberry.
Carbohydrate synthesis is a sub-field of organic chemistry concerned specifically with the generation of natural and unnatural carbohydrate structures. This can include the synthesis of monosaccharide residues or structures containing more than one monosaccharide, known as oligosaccharides.
N-linked glycosylation, is the attachment of an oligosaccharide, a carbohydrate consisting of several sugar molecules, sometimes also referred to as glycan, to a nitrogen atom, in a process called N-glycosylation, studied in biochemistry. The resulting protein is called an N-linked glycan, or simply an N-glycan.
Glucansucrase is an enzyme in the glycoside hydrolase family GH70 used by lactic acid bacteria to split sucrose and use resulting glucose molecules to build long, sticky biofilm chains. These extracellular homopolysaccharides are called α-glucan polymers.
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.
Neopullulanase is an enzyme of the alpha-amylase family with systematic name pullulan 4-D-glucanohydrolase (panose-forming). This enzyme principally catalyses the following chemical reaction by cleaving pullulan's alpha-1,4-glucosidic bonds:
Peptide:N-glycosidase F, commonly referred to as PNGase F, is an amidase of the peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase class. PNGase F works by cleaving between the innermost GlcNAc and asparagine residues of high mannose, hybrid, and complex oligosaccharides from N-linked glycoproteins and glycopeptides. This results in a deaminated protein or peptide and a free glycan.
References
- ↑ "PCEM2 Révisions Biochimie métabolique: Chapitre 13 - Les glycoprotéines" [PCEM2 Metabolic Biochemistry Revision: Chapter 13 - Glycoproteins] (in French). Archived from the original on 2020-07-04. Retrieved 2010-06-11.
- 1 2 3 4 Davies, G; Henrissat, B (15 September 1995). "Structures and mechanisms of glycosyl hydrolases". Structure. 3 (9): 853–59. doi: 10.1016/s0969-2126(01)00220-9 . PMID 8535779.
- ↑ Piszkiewicz, D; Bruice, T.C. (10 April 1968). "Glycoside hydrolysis. II. Intramolecular carboxyl and acetamido group catalysis in 13-glycoside hydrolysis". Journal of the American Chemical Society. 90 (8): 2156–63. doi:10.1021/ja01010a038. PMID 5644189.
- 1 2 Koshland, D.E. (November 1953). "Stereochemistry and the mechanism of enzymatic reactions" (PDF). Biological Reviews. 28 (4): 416–436. doi:10.1111/j.1469-185X.1953.tb01386.x. S2CID 86709302.
- ↑ Plante, O; Palmicci, E (2001). "Seeberger Oligosaccharide Synthesis with Glycosyl Phosphate and Dithiophosphate Triesters as Glycosylating Agents". Journal of the American Chemical Society. 123 (39): 9545–54. doi:10.1021/ja016227r. PMID 11572674.
- ↑ Albert, H; Collin, M; Dudziak, D (30 September 2008). "In vivo enzymatic modulation of IgG glycosylation inhibits autoimmune disease in an IgG subclass-dependent manner". Proceedings of the National Academy of Sciences of the USA. 105 (39): 15005–15009. Bibcode:2008PNAS..10515005A. doi: 10.1073/pnas.0808248105 . PMC 2567483 . PMID 18815375.