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Lysine. Technically, any organic compound with an amine (–NH 2) and a carboxylic acid (–COOH) functional group is an amino acid. The proteinogenic amino acids are a small subset of this group that possess a central carbon atom (α- or 2-) bearing an amino group, a carboxyl group, a side chain and an α-hydrogen levo conformation, with the exception of glycine, which is achiral, and proline ...
Cysteine is chiral, but both D and L-cysteine are found in nature. L‑Cysteine is a protein monomer in all biota, and D-cysteine acts as a signaling molecule in mammalian nervous systems. [8] Cysteine is named after its discovery in urine, which comes from the urinary bladder or cyst, from Greek κύστις kýstis, "bladder". [9]
Cystine is the oxidized derivative of the amino acid cysteine and has the formula (SCH 2 CH(NH 2)CO 2 H) 2.It is a white solid that is poorly soluble in water. As a residue in proteins, cystine serves two functions: a site of redox reactions and a mechanical linkage that allows proteins to retain their three-dimensional structure.
The cystine knot motif stabilizes protein structure and is conserved in proteins across various species. [2] [3] [4] There are three types of cystine knot, which differ in the topology of the disulfide bonds: [5] The growth factor cystine knot (GFCK) inhibitor cystine knot (ICK) common in spider and snail toxins; Cyclic Cystine Knot, or cyclotide
Hydroxylation improves water‐solubility, as well as affecting their structure and function. The most frequently hydroxylated amino acid residue in human proteins is proline . This is because collagen makes up about 25–35% of the protein in our bodies and contains a hydroxyproline at almost every 3rd residue in its amino acid sequence.
A conservative replacement (also called a conservative mutation or a conservative substitution or a homologous replacement) is an amino acid replacement in a protein that changes a given amino acid to a different amino acid with similar biochemical properties (e.g. charge, hydrophobicity and size).
Cysteine has a very reactive sulfhydryl group on its side chain. A disulfide bridge is created when a sulfur atom from one Cysteine forms a single covalent bond with another sulfur atom from a second cysteine in a different part of the protein. These bridges help to stabilize proteins, especially those secreted from cells.
Homocysteine (/ ˌ h oʊ m oʊ ˈ s ɪ s t iː n /; symbol Hcy) is a non-proteinogenic α-amino acid. It is a homologue of the amino acid cysteine, differing by an additional methylene bridge (-CH 2-). It is biosynthesized from methionine by the removal of its terminal C ε methyl group.