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SEA Native Peptide Ligation
Protein chemical synthesis by native peptide ligation of unprotected peptide segments is an interesting complement and potential alternative to the use of living systems for producing proteins. The synthesis of proteins requires efficient native peptide ligation methods, which enable the chemoselective formation of a native peptide bond in aqueous solution between unprotected peptide segments. The most frequently used technique for synthesizing proteins is Native chemical ligation (NCL). However, alternatives are emerging, one of which is SEA Native Peptide Ligation. Overview The SEA group belongs to the ''N,S''-acyl shift systems because its reactivity is dictated by the intramolecular nucleophilic addition of one SEA thiol group on the C-terminal carbonyl group of the peptide segment. This results in the migration of the peptide chain from the nitrogen to the sulfur. The overall process of SEA native peptide ligation involves first an ''N,S''-acyl shift for in ''in situ'' form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Ligation
Chemical ligation is a set of techniques used for creating long peptide or protein chains. It is the second step of a convergent approach. First, smaller peptides containing 30-50 amino acids are prepared by conventional chemical peptide synthesis. Then, they are completely deprotected. Chemical ligation is the technique of coupling these peptides by chemoselective reaction to give a unique reaction product, usually in aqueous solution. With several coupling steps, proteins of up to 200-300 amino acids can be produced. Methods of chemical ligation There are various techniques described in literature. Native chemical ligation The most practical and robust method for the chemoselective reaction of unprotected peptides is native chemical ligation. Native chemical ligation has overcome the limitations of the classical synthetic organic chemistry approach to the total synthesis of proteins, and enables the routine total or semi- synthesis of protein molecules. The original chemica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peptide
Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A polypeptide is a longer, continuous, unbranched peptide chain. Hence, peptides fall under the broad chemical classes of biological polymers and oligomers, alongside nucleic acids, oligosaccharides, polysaccharides, and others. A polypeptide that contains more than approximately 50 amino acids is known as a protein. Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to ligands such as coenzymes and cofactors, or to another protein or other macromolecule such as DNA or RNA, or to complex macromolecular assemblies. Amino acids that have been incorporated into peptides are termed residues. A water molecule is released during formation of each amide bond.. All peptides except cyc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemoselective
Chemoselectivity is the preferential outcome of a chemical reaction over a set of possible alternative reactions. In another definition, chemoselectivity refers to the selective reactivity of one functional group in the presence of others; often this process in convoluted and protecting groups are on the molecular connectivity alone. Such predictions based on connectivity are generally considered plausible, but the physical outcome of the actual reaction is ultimately dependent on a number of factors that are practically impossible to predict to any useful accuracy (solvent, atomic orbitals, etc.). Chemoselectivity can be difficult to predict, but observing selective outcomes in cases where many reactions are plausible, is common. Examples include the selective organic reduction of the greater relative chemoselectivity of sodium borohydride reduction versus lithium aluminium hydride reduction. In another example, the compound 4-methoxyacetophenone is oxidized by bleach at the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peptide Bond
In organic chemistry, a peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide or protein chain. It can also be called a eupeptide bond to distinguish it from an isopeptide bond, which is another type of amide bond between two amino acids. Synthesis When two amino acids form a ''dipeptide'' through a ''peptide bond'', it is a type of condensation reaction. In this kind of condensation, two amino acids approach each other, with the non- side chain (C1) carboxylic acid moiety of one coming near the non-side chain (N2) amino moiety of the other. One loses a hydrogen and oxygen from its carboxyl group (COOH) and the other loses a hydrogen from its amino group (NH2). This reaction produces a molecule of water (H2O) and two amino acids joined by a peptide bond (−CO−NH−). The two joined amino acids are called a dipeptide. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Native Chemical Ligation
Native Chemical Ligation (NCL) is an important extension of the chemical ligation concept for constructing a larger polypeptide chain by the covalent condensation of two or more unprotected peptides segments. Native chemical ligation is the most effective method for synthesizing native or modified proteins of typical size (''i.e.'', proteins< ~300 AA). Reaction In native chemical ligation, the ionized group of an residue of an unprotected peptide attacks the[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophilic
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases. ''Nucleophilic'' describes the affinity of a nucleophile to bond with positively charged atomic nuclei. Nucleophilicity, sometimes referred to as nucleophile strength, refers to a substance's nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge, and nucleophilic addition. Nucleophilicity is closely related to basicity. History The terms ''nucleophile'' and '' electrophile'' were introduced by Christopher Kelk Ingold in 1933, replacing the terms ''anionoid'' and ''cationoid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl group, or a sulfanyl group. Thiols are the sulfur analogue of alcohols (that is, sulfur takes the place of oxygen in the hydroxyl () group of an alcohol), and the word is a blend of "''thio-''" with "alcohol". Many thiols have strong odors resembling that of garlic or rotten eggs. Thiols are used as odorants to assist in the detection of natural gas (which in pure form is odorless), and the "smell of natural gas" is due to the smell of the thiol used as the odorant. Thiols are sometimes referred to as mercaptans () or mercapto compounds, a term introduced in 1832 by William Christopher Zeise and is derived from the Latin ('capturing mercury')''Oxford American Dictionaries'' ( Mac OS X Leopard). because the thiolate group () bonds very stro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C-terminal
The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is translated from messenger RNA, it is created from N-terminus to C-terminus. The convention for writing peptide sequences is to put the C-terminal end on the right and write the sequence from N- to C-terminus. Chemistry Each amino acid has a carboxyl group and an amine group. Amino acids link to one another to form a chain by a dehydration reaction which joins the amine group of one amino acid to the carboxyl group of the next. Thus polypeptide chains have an end with an unbound carboxyl group, the C-terminus, and an end with an unbound amine group, the N-terminus. Proteins are naturally synthesized starting from the N-terminus and ending at the C-terminus. Function C-terminal retention signals While the N-terminus of a protein often con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbonyl Group
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a carbonyl group is often referred to as a carbonyl compound. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal carbonyl, e.g. nickel carbonyl). The remainder of this article concerns itself with the organic chemistry definition of carbonyl, where carbon and oxygen share a double bond. Carbonyl compounds In organic chemistry, a carbonyl group characterizes the following types of compounds: Other organic carbonyls are urea and the carbamates, the derivatives of acyl chlorides chloroformates and phosgene, carbonate esters, thioesters, lactones, lactams, hydroxamates, and isocyanates. Examples of inorganic carbonyl compounds are carbon dioxide and carbonyl su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thioester
In organic chemistry, thioesters are organosulfur compounds with the functional group . They are analogous to carboxylate esters () with the sulfur in the thioester playing the role of the linking oxygen in the carboxylate ester, as implied by the ''thio-'' prefix. They are the product of esterification between a carboxylic acid () and a thiol (). In biochemistry, the best-known thioesters are derivatives of coenzyme A, e.g., acetyl-CoA.Matthys J. Janssen "Carboxylic Acids and Esters" in PATAI's Chemistry of Functional Groups: Carboxylic Acids and Esters, Saul Patai, Ed. John Wiley, 1969, New York: pp. 705–764. Synthesis The most typical route to thioester involves the reaction of an acid chloride with an alkali metal salt of a thiol: :RSNa + R'COCl -> R'COSR + NaCl Another common route entails the displacement of halides by the alkali metal salt of a thiocarboxylic acid. For example, thioacetate esters are commonly prepared by alkylation of potassium thioacetate: :CH3COSK + ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SEA Native Peptide Ligation
Protein chemical synthesis by native peptide ligation of unprotected peptide segments is an interesting complement and potential alternative to the use of living systems for producing proteins. The synthesis of proteins requires efficient native peptide ligation methods, which enable the chemoselective formation of a native peptide bond in aqueous solution between unprotected peptide segments. The most frequently used technique for synthesizing proteins is Native chemical ligation (NCL). However, alternatives are emerging, one of which is SEA Native Peptide Ligation. Overview The SEA group belongs to the ''N,S''-acyl shift systems because its reactivity is dictated by the intramolecular nucleophilic addition of one SEA thiol group on the C-terminal carbonyl group of the peptide segment. This results in the migration of the peptide chain from the nitrogen to the sulfur. The overall process of SEA native peptide ligation involves first an ''N,S''-acyl shift for in ''in situ'' form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometimes the symbol Cyz is used. The deprotonated form can generally be described by the symbol Cym as well. The thiol is susceptible to oxidation to give the disulfide derivative cystine, which serves an important structural role in many proteins. In this case, the symbol Cyx is sometimes used. When used as a food additive, it has the E number E920. Cysteine is encoded by the codons UGU and UGC. The sulfur-containing amino acids cysteine and methionine are more easily oxidized than the other amino acids. Structure Like other amino acids (not as a residue of a protein), cysteine exists as a zwitterion. Cysteine has chirality in the older / notation based on homology to - and -glyceraldehyde. In the newer ''R''/''S'' system of design ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
