Protein Post-Translational Modifications (PTMs) Explained
Protein post-translational modifications (PTMs) such as phosphorylation, glycosylation, ubiquitination, and more play vital roles in cell biology and disease. Understanding PTMs is crucial for advancing research in these areas.
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StudyMafia.Org PTMs Submitted To: Submitted By: Studymafia.org Studymafia.org
Table Contents Definition Introduction Components of PTMs Conclusion 2
Definition Protein post-translational modifications (PTMs) increase the functional diversity of the proteome by the covalent addition of functional groups or proteins, proteolytic cleavage of regulatory subunits, or degradation of entire proteins. 3
Introduction These modifications include phosphorylation, glycosylation, ubiquitination, nitrosylation, methylation, acetylation, lipidation and proteolysis and influence almost all aspects of normal cell biology and pathogenesis. Therefore, identifying and understanding PTMs is critical in the study of cell biology and disease treatment and prevention. 4
Components of PTMs Phosphorylation Reversible protein phosphorylation, principally on serine, threonine or tyrosine residues, is one of the most important and well-studied post- translational modifications. Phosphorylation plays critical roles in the regulation of many cellular processes, including cell cycle, growth, apoptosis and signal transduction pathways. 6
Components of PTMs Glycosylation Protein glycosylation is acknowledged as one of the major post-translational modifications, with significant effects on protein folding, conformation, distribution, stability and activity. Glycosylation encompasses a diverse selection of sugar-moiety additions to proteins that ranges from simple monosaccharide modifications of nuclear transcription factors to highly complex branched polysaccharide changes of cell surface receptors. 7
Components of PTMs Ubiquitination Ubiquitin is an 8-kDa polypeptide consisting of 76 amino acids that is appended to the -NH2 of lysine in target proteins via the C-terminal glycine of ubiquitin. Following an initial monoubiquitination event, the formation of a ubiquitin polymer may occur, and polyubiquitinated proteins are then recognized by the 26S proteasome that catalyzes the degradation of the ubiquitinated protein and the recycling of ubiquitin. 8
Components of PTMs S-nitrosylation Nitric oxide (NO) is produced by three isoforms of nitric oxide synthase (NOS), and it is a chemical messenger that reacts with free cysteine residues to form S- nitrothiols (SNOs). 9
Components of PTMs Methylation The transfer of one-carbon methyl groups to nitrogen or oxygen (N- and O-methylation, respectively) to amino acid side chains increases the hydrophobicity of the protein and can neutralize a negative amino acid charge when bound to carboxylic acids. 10
Components of PTMs N-acetylation N-acetylation, or the transfer of an acetyl group to nitrogen, occurs in almost all eukaryotic proteins through both irreversible and reversible mechanisms. N-terminal acetylation requires the cleavage of the N-terminal methionine by methionine aminopeptidase (MAP) before replacing the amino acid with an acetyl group from acetyl-CoA by N-acetyltransferase (NAT) enzymes. 11
Components of PTMs Lipidation Lipidation is a method to target proteins to membranes in organelles (endoplasmic reticulum [ER], Golgi apparatus, mitochondria), vesicles (endosomes, lysosomes) and the plasma membrane. 12
Components of PTMs Proteolysis Peptide bonds are indefinitely stable under physiological conditions, and therefore cells require some mechanism to break these bonds. Proteases comprise a family of enzymes that cleave the peptide bonds of proteins and are critical in antigen processing, apoptosis, surface protein shedding and cell signaling. 13
Conclusion Posttranslational modifications (PTMs) are covalent processing events that change the properties of a protein by proteolytic cleavage and adding a modifying group, such as acetyl, phosphoryl, glycosyl and methyl, to one or more amino acids. 15
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