POST TRANSLATIONAL MODIFICATIONS:

POST TRANSLATIONAL MODIFICATIONS: 

  • Post Translational modifications are chemical modifications which play a critical role in functional proteomics, because it regulate  position, activity and interaction with other cellular molecules like proteins, lipids, nucleic acids, and cofactors  etc.
  • Post Translational modifications occur at different amino acids side chains or  at peptide linkages and is carried out by different enzymes  like phosphatases, kinases, transferases and ligases which main function are mainly addition or removal of different functional groups or sugars to or from amino acids side chain.
  • And it also involves the proteases, which main function is to cleave peptide bonds or to remove specific sequences or regulatory subunits from a large polypeptide.
  • Post Translational modifications can also be reversible or irreversible, it basically depend upon the nature of the protein modification.

Types of post translational modification:

PHOSPHORYLATION: 
  • Phosphorylation is an important post-translational modification.
  • First it acts to functionally regulate the catalytic activity of the protein by defining a rigid and permanent 3-D protein structure.
  • Secondly, temporarily phosphorylate proteins serve as anchors for other protein substrates in signal transduction pathways.
  • As, such it acts as a key-player in the regulation of many cellular processes like cell-cycle, cell growth, apoptosis and regulation of signal transduction pathways






Glycosylation: 
  • Glycosylation is a function of the biosynthetic-secretory pathway in the endoplasmic reticulum (ER) and Golgi apparatus. Approximately 50% proteins characteristically expressed in a cell go through this alteration, which involves the covalent addition of sugar moieties to specific amino acids.
  • Mostly, soluble and membrane-bound proteins expressed in the endoplasmic reticulum undergo glycosylation , including  all secreted proteins, surface receptors and ligands .
  • Moreover, some proteins that are transferred from the Golgi to the cytoplasm are also glycosylated.
Ubiquitinization:  
  • This is one another post-translational modification where ubiquitin is added to protein. Ubiquitin is the eukaryotic protein made of 76 amino acids and has a molecular mass of about 8.5 kDa in mammals. 
  • In ubiquitinization, It marks the cellular protein for the process of degradation via proteosome, changes protein’s location, prevent or promote protein-protein interaction.
Methylation: 
  • This process refers to addition of methyl group to Nitrogen (N-methylation) or Oxygen (O-methylation) to amino acid side chain.
  • N-methylation is irreversible whereas O-methylation is potentially reversible. Methylation enhances hydrophobicity of amino acid and neutralizes negative charge when attached to carboxylic acid.
  • Main methyl group contributor for such reaction is SAM (S-adenosyl methionine). This reaction is mediated by enzyme methyltransferases. Methylation process is involved in epi-genetic regulation as histone methylation and demethylation.

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