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Posttranslational modification means the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis for many proteins.Posttranslational modification may involve the formation of disulfide bridges and attachment of any of a number of biochemical functional groups, such as acetate, phosphate, various lipids and carbohydrates. Enzymes may also remove one or more amino acids from the amino end of the polypeptide chain, or cut the polypeptide in the middle of the chain. For instance, the peptide hormone insulin is cut twice after disulfide bond formation to remove a propeptide from the middle of the chain, leaving a protein consisting of two polypeptide chains connected by disulfide bonds. In other cases, two or more polypeptide chains that are synthesized separately may associate to become subunits of a protein with quaternary structure.
A protein is a chain composed of a long sequence of 20 possible amino acids, also called a polypeptide. Some posttranslational modification extends the range of possible functions a protein can have by introducing other chemical groups into the makeup of a protein (e.g., carbohydrate chains). Such chemical changes may alter the hydrophobicity of a protein and thus determine if the modified protein is cytosolThe cytosol (as opposed to cytoplasm which also includes the organelles) is the internal fluid of the cell, and a large part of cell metabolism occurs here. Proteins within the cytosol play an important role in signal transduction pathways, glycolysis, anic or membrane-bound. Other modifications like phosphorylationIn biochemistry, phosphorylation is the addition of a phosphate (PO) group to a protein or a small molecule. Its prominent role in biochemistry is the subject of a very large body of research (the Medline database returns over 100,000 articles on the subj are part of common mechanisms for controlling the behavior of a protein, for instance, activating or inactivating an enzyme.
Types of posttranslational modifications include:
- phosphorylationIn biochemistry, phosphorylation is the addition of a phosphate (PO) group to a protein or a small molecule. Its prominent role in biochemistry is the subject of a very large body of research (the Medline database returns over 100,000 articles on the subj, the addition of a phosphate group, usual to serineSerine is one of the 20 most common natural amino acids on Earth. As a constituent (residue) of proteins, its side chain can undergo O-linked glycosylation. This might be important in explaining some of the devastating consequences of diabetes. It is one, tyrosine, threonine or histidine
- acetylation, the addition of an acetyl group, usually at the N-terminus of the protein
- isoprenylation, the addition of an isoprenoid group (e.g. farnesol and geranylgeraniol)
- glycosylation, the addition of a glycosyl group to either asparagine, hydroxylysine, serine, or threonine, resulting in a glycoprotein
- the GPI anchor
Gene expression
