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Asx Turn
The Asx turn is a structural feature in proteins and polypeptides. It consists of three amino acid residues (labeled i, i+1 and i+2) in which residue i is an aspartate (Asp) or asparagine (Asn) that forms a hydrogen bond from its sidechain CO group to the mainchain NH group of residue i+2. About 14% of Asx residues present in proteins belong to Asx turns. The name "Asx" is used here to represent either of the amino acids aspartate (Asp) or asparagine (Asn). Types Four types of Asx turn can be distinguished: types I, I’, II and II’. These categories correspond to those of the better-known hydrogen-bonded beta turns, which have four residues and a hydrogen bond between the CO of residue i and the NH of residue i+3. Asx turns and beta turns have structurally similar hydrogen-bonded loops and exhibit sidechain-mainchain mimicry in the sense that the sidechain of residue i of the Asx turn mimics the mainchain of residue i of the beta turn. Regarding their occurrence in prote ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proteins
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, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific 3D structure that determines its activity. A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides. The individual amino acid residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of amino acid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polypeptides
Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. Peptides fall under the broad chemical classes of biological polymers and oligomers, alongside nucleic acids, oligosaccharides, polysaccharides, and others. Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to ligands such as coenzymes and cofactors, 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 cyclic peptides have an N-terminal (amine group) and C-terminal (carboxyl group) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amino Acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 appear in the genetic code of life. Amino acids can be classified according to the locations of the core structural functional groups ( alpha- , beta- , gamma- amino acids, etc.); other categories relate to polarity, ionization, and side-chain group type ( aliphatic, acyclic, aromatic, polar, etc.). In the form of proteins, amino-acid '' residues'' form the second-largest component (water being the largest) of human muscles and other tissues. Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis. It is thought that they played a key role in enabling life on Earth and its emergence. Amino acids are formally named by the IUPAC- IUBMB Joint Commi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aspartate
Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. The L-isomer of aspartic acid is one of the 22 proteinogenic amino acids, i.e., the building blocks of proteins. D-aspartic acid is one of two D-amino acids commonly found in mammals. Apart from a few rare exceptions, D-aspartic acid is not used for protein synthesis but is incorporated into some peptides and plays a role as a neurotransmitter/ neuromodulator. Like all other amino acids, aspartic acid contains an amino group and a carboxylic acid. Its α-amino group is in the protonated –NH form under physiological conditions, while its α-carboxylic acid group is deprotonated −COO− under physiological conditions. Aspartic acid has an acidic side chain (CH2COOH) which reacts with other amino acids, enzymes and proteins in the body. Under physiological conditions (pH 7.4) in proteins the side chain usually occurs as the negatively charged as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asparagine
Asparagine (symbol Asn or N) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO− form under biological conditions), and a side chain carboxamide, classifying it as a polar (at physiological pH), aliphatic amino acid. It is non-essential in humans, meaning the body can synthesize it. It is encoded by the codons AAU and AAC. The one-letter symbol N for asparagine was assigned arbitrarily, with the proposed mnemonic asparagi''N''e; History Asparagine was first isolated in 1806 in a crystalline form by French chemists Louis Nicolas Vauquelin and Pierre Jean Robiquet (then a young assistant). It was isolated from asparagus juice, in which it is abundant, hence the chosen name. It was the first amino acid to be isolated. Three years later, in 1809, Pierre Jean Robiquet identified a substance from l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen Bond
In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently bonded to a more Electronegativity, electronegative donor atom or group (Dn), interacts with another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor (Ac). Unlike simple Dipole–dipole attraction, dipole–dipole interactions, hydrogen bonding arises from charge transfer (nB → σ*AH), Atomic orbital, orbital interactions, and quantum mechanical Delocalized electron, delocalization, making it a resonance-assisted interaction rather than a mere electrostatic attraction. The general notation for hydrogen bonding is Dn−H···Ac, where the solid line represents a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The most frequent donor and acceptor atoms are nitrogen (N), oxyg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Figure Of Asx-turn
Figure may refer to: General *A shape, drawing, depiction, or geometric configuration *Figure (wood), wood appearance *Figure (music), distinguished from musical motif *Noise figure, in telecommunication * Dance figure, an elementary dance pattern *A person's figure, human physical appearance *Figure–ground (perception), the distinction between a visually perceived object and its surroundings Arts *Figurine, a miniature statuette representation of a creature *Action figure, a posable jointed solid plastic character figurine *Figure painting, realistic representation, especially of the human form *Figure drawing *Model figure, a scale model of a creature Writing *figure, in writing, a type of floating block (text, table, or graphic separate from the main text) *Figure of speech, also called a rhetorical figure *Christ figure, a type of character * in typesetting, text figures and lining figures Accounting *Figure, a synonym for number *Significant figures in a decimal numb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beta Turn
β turns (also β-bends, tight turns, reverse turns, Venkatachalam turns) are the most common form of turns—a type of non-regular secondary structure in proteins that cause a change in direction of the polypeptide chain. They are very common motifs in proteins and polypeptides. Each consists of four amino acid residues (labelled ''i'', ''i+1'', ''i+2'' and ''i+3''). They can be defined in two ways: # By the possession of an intra-main-chain hydrogen bond between the CO of residue ''i'' and the NH of residue ''i+3''; # By having a distance of less than 7Å between the Cα atoms of residues ''i'' and ''i+3''. The hydrogen bond criterion is the one most appropriate for everyday use, partly because it gives rise to four distinct categories; the distance criterion gives rise to the same four categories but yields additional turn types. Definition Hydrogen bond criterion The hydrogen bond criterion for beta turns, applied to polypeptides whose amino acids are linked by tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ST Turn
The ST turn is a structural feature in proteins and polypeptides. Each consists of three amino acid residues (labeled ''i'', ''i'' + 1 and ''i'' + 2) in which residue ''i'' is a serine (S) or threonine (T) that forms a hydrogen bond from its sidechain oxygen group to the mainchain NH group of residue ''i'' + 2. Similar Structural motif, motifs occur with aspartate or asparagine as residue ''i'', called asx turn. Four types of asx turn and ST turn can be distinguished: types I, I’, II and II’. These categories correspond (via sidechain-mainchain mimicry of residue i) to those of the more abundant hydrogen-bonded beta turns, which have four residues and a hydrogen bond between the CO of residue ''i'' and the NH of residue ''i'' + 3. Regarding their occurrence in proteins, they differ in that type I is the commonest of the four beta turns while type II’ is the commonest of the ST and asx turns. Asx and ST turns both occur frequently at th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
N-termini
The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the amine group is bonded to the carboxylic group of another amino acid, making it a chain. That leaves a free carboxylic group at one end of the peptide, called the C-terminus, and a free amine group on the other end called the N-terminus. By convention, peptide sequences are written N-terminus to C-terminus, left to right (in LTR writing systems). This correlates the translation direction to the text direction, because when a protein is translated from messenger RNA, it is created from the N-terminus to the C-terminus, as amino acids are added to the carboxyl end of the protein. Chemistry Each amino acid has an amine group and a carboxylic group. Amino acids link to one another by peptide bonds which form through a dehydration reaction that j ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
α-helices
An alpha helix (or α-helix) is a sequence of amino acids in a protein that are twisted into a coil (a helix). The alpha helix is the most common structural arrangement in the secondary structure of proteins. It is also the most extreme type of local structure, and it is the local structure that is most easily predicted from a sequence of amino acids. The alpha helix has a right-handed helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid that is four residues earlier in the protein sequence. Other names The alpha helix is also commonly called a: * Pauling–Corey–Branson α-helix (from the names of three scientists who described its structure) * 3.613-helix because there are 3.6 amino acids in one ring, with 13 atoms being involved in the ring formed by the hydrogen bond (starting with amidic hydrogen and ending with carbonyl oxygen) Discovery In the early 1930s, William Astbury showed that there were dras ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asx Motif
The Asx motif is a commonly occurring feature in proteins and polypeptides. It consists of four or five amino acid residues with either aspartate or asparagine as the first residue (residue i). It is defined by two internal hydrogen bonds. One is between the side chain oxygen of residue i and the main chain NH of residue i+2 or i+3; the other is between the main chain oxygen of residue i and the main chain NH of residue i+3 or i+4. Asx motifs occur commonly in proteins and polypeptides. When one of the hydrogen bonds is between the main chain oxygen of residue i and the side chain NH of residue i+3 the motif incorporates a beta turn. When one of the hydrogen bonds is between the side chain oxygen of residue i and the main chain NH of residue i+2 the motif incorporates an Asx turn. As with Asx turns, a significant proportion of Asx motifs occur at the N-terminus of an alpha helix with the Asx as the N cap residue. Asx motifs have thus often been described as helix capping fe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
