Post-translational modifications are a set of diverse biological processes that chemically alter the amino acids within a protein after it has been translated by the ribosome [2]. Some common examples include the addition of chemical groups such as phosphates (phosphorylation) or ubiquitin (ubiquitination), proteolytic cleavage, or addition of bonds like disulfide bridges [3]. These modifications can either be made permanent or may change over time. In general, post-translational modifications increase the functional diversity of the proteome and can alter an individual proteins stability, folding, targeting or recognition [4].
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Phosphorylation is one of the most common post-translational modifications and is simply the action of kinases adding phosphate groups onto amino acids within the protein. Often times threonine, serine and tyrosine are the phosphorylated amino acids. Phosphorylation allows for a major molecular mechanism through which protein function can be regulated in response to extracellular stimuli. Virtually all types of extracellular signals produce most of their diverse physiological effects by regulating phosphorylation of specific phosphoproteins in their target cells. The majority of neuronal proteins are regulated by phosphorylation [5].
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