The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal end, or COOH-terminus) of a protein or polypeptide is the end of the amino acid chain terminated by a free carboxyl group (-COOH). Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Carboxyl group or CO2H is a Functional group present in Amino acids and Carboxylic acids Its structure is composed of one carbon atom attached 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.
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Chemistry
Each amino acid has a carboxyl group and an amine group, and amino acids link to one another to form a chain by a dehydration reaction by joining the amine group of one amino acid to the carboxyl group of the next. Amines are Organic compounds and Functional groups that contain a basic Nitrogen Atom with a Lone pair. In Chemistry, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule Thus polypeptide chains have an end with an unbound carboxyl group, the C-terminus, and an end with an amine group, the N-terminus. The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or Proteins are 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 contains targeting signals, the C-terminus can contain retention signals for protein sorting. The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or The most common ER retention signal is the amino acid sequence -KDEL (or -HDEL) at the C-terminus, which keeps the protein in the endoplasmic reticulum and prevents it from entering the secretory pathway. ER retention refers to Proteins that are retained in the Endoplasmic reticulum, or ER after folding; these are known as ER resident proteins The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle The secretory pathway is a series of steps a cell uses to move Proteins out of the cell a process known as secretion.
C-terminal modifications
The C-terminus of proteins can be modified posttranslationally, most commonly by the addition of a lipid anchor to the C-terminus that allows the protein to be inserted into a membrane without having a transmembrane domain. Posttranslational modification (PTM is the chemical modification of a Protein after its translation. Lipids are broadly defined as any fat- Soluble ( lipophilic) naturally-occurring Molecule, such as fats oils waxes cholesterol sterols fat-soluble Transmembrane domain usually denotes a single transmembrane Alpha helix of a Transmembrane protein.
- Prenylation
One form of C-terminal modification is prenylation. Prenylation or isoprenylation or lipidation is the addition of Hydrophobic molecules to a Protein. Prenylation or isoprenylation or lipidation is the addition of Hydrophobic molecules to a Protein. During prenylation, a farnesyl- or geranylgeranyl-isoprenoid membrane anchor is added to a cysteine residue near the C-terminus. Farnesyl pyrophosphate (FPP is an intermediate in the HMG-CoA reductase pathway used by organisms in the biosynthesis of Terpenes and Terpenoids It Geranylgeranyl pyrophosphate is an intermediate in the HMG-CoA reductase pathway used by organisms in the biosynthesis of Terpenes and Terpenoids In plants Small, membrane-bound G proteins are often modified this way. GTP chemical structurepng|thumb|180px| Guanosine triphosphate]] G proteins short for guanine nucleotide-binding proteins, are a family of Proteins involved
- GPI anchors
Another form of C-terminal modification is the addition of a phosphoglycan, glycosylphosphatidylinositol (GPI), as a membrane anchor. Glycosylphosphatidylinositol ( GPI anchor) is a Glycolipid that can be attached to the C-terminus of a Protein during Posttranslational Glycosylphosphatidylinositol ( GPI anchor) is a Glycolipid that can be attached to the C-terminus of a Protein during Posttranslational The GPI anchor is attached to the C-terminus after proteolytic cleavage of a C-terminal propeptide. The most prominent example for this type of modification is the prion protein. A prion (ˈpriːɒn is thought to be an infectious agent that according to current scientific consensus is comprised entirely of a propagated, mis-folded
C-terminal domain or Carboxyl Tail Domain
The C-terminal domain (CTD) of some proteins has specialized functions.
 RNA POL II in action. |
- CTD of RNA polymerase
The carboxy-terminal domain of RNA polymerase II typically consists of up to 52 repeats of the sequence Tyr-Ser-Pro-Thr-Ser-Pro-Ser [1]. RNA polymerase II (also called RNAP II and Pol II) is an enzyme found in eukaryotic cells Other proteins often bind the C-terminal domain of RNA polymerase in order to activate polymerase activity. It is the protein domain which is involved in the initiation of DNA transcription, the capping of the RNA transcript, and attachment to the spliceosome for RNA splicing[2]. Transcription is the synthesis of RNA under the direction of DNA Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product A spliceosome is a complex of specialized RNA and Protein subunits that removes Introns from a transcribed pre- mRNA ( HnRNA In Molecular biology, splicing is a modification of an RNA after transcription, in which Introns are removed and Exons are joined
See also
References
The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end orDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic