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Plus de Department of Biotechnology, Kamaraj college of engineering and technology(20)


post translational modification.pptx

  1. Post Translational Modifications of Proteins
  2. • It is the chemical modification of protein after its translation. • Key role in functional Proteomics. • They regulate activity, localization and interaction with other cellular molecules such as proteins, nucleic acids, lipids and cofactors. Introduction
  3. Types of PTM’s • Trimming • Covalent Attachment • Protein Folding • Protein Degradation
  4. Trimming • Insulin is synthesized in the cells and it is in inactive form that it is can’t perform it’s function. • For the proper functioning of the insulin, its post translational modifications occurs that have involve the removal of the part of protein to convert it into three dimensional and fully active form
  5. • Phosphorylation • Glycosylation • Ubiquitination • S-Nitrosylation • Methylation • N-Acetylation • Lipidation • Proteolysis Types of Post Translational Modifications of Proteins
  6. Phosphorylation • Addition of phosphate group to a protein. • Principally on serine, threonine or tyrosine residues. • Also known as Phospho regulation. • Critical role in cell cycle, growth, apoptosis and signal transduction pathways. Protein kinases ATP + protein ———————> phosphoprotein + ADP
  7. Phosphorylation
  8. Example
  9. • The covalent attachment of oligosaccharides • Addition of glycosyl group or carbohydrate group to a protein. • Principally on Asparagine, hydroxylysine, serine or threonine. • Significant effect on protein folding, conformation, distribution, stability and activity. Glycosylation
  10. Example
  11. • N-Linked glycans – attached to nitrogen of Asparagine or arginine side chains. • O-Linked glycans – attached to hydroxy oxygen of serine,threonine • Phospho glycans – linked through the phosphate of serine. • C-Linked glycans – Rare form, Sugar is added to a carbon on tryptophan side chain. Classes of Glycans
  12. • Ubiquitin is a small regulatory protein that can be attached to the proteins and label them for destruction. • Effects in cell cycle regulation, control of proliferation and differentiation, programmed cell death (apoptosis), DNA repair, immune and inflammatory processes and organelle biogenesis. Ubiquitination
  13. Ubiquitin cycle
  14. • Nitrosyl (NO) group is added to the protein. • NO a chemical messanger that reacts with free cysteine residues to form S-nitrothiols. • Used by cells to stabilize proteins, regulate gene expression. S-Nitrosylation
  15. • Addition of methyl group to a protein. • Usually at lysine or arginine residues. • Binds on nitrogen and oxygen of proteins • Methyl donor is S-adenosylmethionine (SAM) • Enzyme for this is methyltransferase • Methylation of lysine residues in histones in DNA is important regulator of chromatin structure Alkylation/Methylation
  16. Example Where SAM (S-adenosyl methionine) is converted into SAH(S-adenosyl homocysteine)
  17. • Addition of acetyl group to the nitrogen. • Histones are acetylated on lysine residues in the N-terminal tail as a part of gene regulation. • Involved in regulation of transcription factors, effector proteins, molecular chaperons and cytoskeletal proteins. • Methionine aminopeptidase (MAP) is an enzyme responsible for N-terminal acetylation N-Acetylation
  18. Example
  19. Where, HDACs = Histone deactyllase , KATs= N-acetyltransferase.
  20. • Lipidation attachment of a lipid group, such as a fatty acid, covalently to a protein. • In general, lipidation helps in cellular localization and targeting signals, membrane tethering and as mediator of protein-protein interactions. Lipidation
  21. • C-terminal glycosyl phosphatidylinositol (GPI) anchor • N-terminal myristoylation • S-palmitoylation • S-prenylation Types of lipidation
  22. C-terminal glycosyl phosphatidylinositol (GPI) anchor • GPI anchors tether cell surface proteins to the plasma membrane • GPI-anchored proteins are often localized to cholesterol- and sphingolipid-rich lipids, which act as signaling platforms on the plasma membrane.
  23. N-myristoylation • It is the attachment of myristoyl group a 14- carbon saturated fatty acid (C14) to a protein. • It is facilitated by N-myristoyltransferase (NMT) and uses myristoyl-CoA as the substrate.
  24. S-palmitoylation • It is addition of C16 palmitoyl group from palmitoyl-CoA • Palmitoyl acyl transferases (PATs)enzyme favors this step. • Reversed by thioesterases
  25. S-prenylation • Addition of a farnesyl (C15) or geranylgeranyl (C20) group to proteins. • Enzyme involved in this reaction is farnesyl transferase (FT) or geranylgeranyl transferases (GGT I and II).
  26. Disulfide Bonding • Disulfide bonds are covalent bonds formed between two cysteine residues (R-S-S-R). • These bonds contribute to the correct folding of proteins as other elements of secondary structure
  27. Disulfide Bonding
  28. • Cleavage of peptide bonds by proteases. • Examples of Proteases- Serine Proteases, Cysteine Proteases, Aspartic acid Proteases. • Involved in Antigen processing, Apoptosis, Cell signalling Proteolysis
  29. • Mass spectrometry • HPLC analysis • Incorporation of radioactive groups by addition to growing cells and chromatographic – e.g., 75Se-labeling isolation of proteins • Antibody cross-reactivity – e.g., antibody against phosphotyrosine • Polyacrylamide gel electrophoresis (PAGE) Identification of modifications