post translational modification.pptx

Molecular Biology

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. Ph o sp h o r yl a tion

8. E x ample

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. E x ample

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 . U s ed b y cells t o st a bili z e p r o t eins, r egul a t e 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. E x ample 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 - Ac e tyl a tion

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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. Lipid a tion

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 I t i s the a tt achme n t of m yri s t oy l g r ou p 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 - palmi t o yl a tion 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 . , 75 S e - lab e l i ng isolation of proteins Antibody cross-reactivity – e.g. , antibody against phosphotyrosine Polyacrylamide gel electrophoresis (PAGE) Identification of modifications

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