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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

5. • Phosphorylation
• Glycosylation
• Ubiquitination
• S-Nitrosylation
• Methylation
• N-Acetylation
• Lipidation
• Proteolysis
Types of Post Translational
Modifications of Proteins

7. • 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.
Phosphorylation
Protein kinases
ATP + protein ———————> phosphoprotein + ADP

8. Phosphorylation

9. Example

10. • 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

11. Example

12. • 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

13. • 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

14. Ubiquitin cycle

16. • 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

18. • 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

19. Example
Where SAM (S-adenosyl methionine) is converted into SAH(S-adenosyl homocysteine)

20. • 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

21. Example

22. Where,
HDACs = Histone deactyllase ,
KATs = N-acetyltransferase.

23. • 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

24. • C-terminal glycosyl phosphatidylinositol (GPI)
anchor
• N-terminal myristoylation
• S-palmitoylation
• S-prenylation
Types of lipidation

25. 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.

26. 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.

27. S-palmitoylation
• It is addition of C16 palmitoyl group from
palmitoyl-CoA
• Palmitoyl acyl transferases (PATs) enzyme
favors this step.
• Reversed by thioesterases

29. 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).

30. 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

31. Disulfide Bonding

32. • Cleavage of peptide bonds by proteases.
• Examples of Proteases- Serine Proteases,
Cysteine Proteases, Aspartic acid Proteases.
• Involved in Antigen processing, Apoptosis, Cell
signalling
Proteolysis

34. • Mass spectrometry
• HPLC analysis
• Incorporation of radioactive groups by addition to
growing cells
– e.g., 75Se-labeling and chromatographic
isolation of proteins
• Antibody cross-reactivity
– e.g., antibody against phosphotyrosine
• Polyacrylamide gel electrophoresis (PAGE)
Identification of modifications

35. Identification of modifications
small-molecule modifications can affect not only the activity, but also the structure of
proteins, much as ligands such as ATP can affect the activity and structure of proteins
use 2D gel electrophoresis to
detect modified proteins in
whole-cell (or partly purified)
lysates
O-GlcNAc is an abundant modification of nucleocytoplasmic proteins.
Nucleo-cytoplasmic proteins from HeLa cells were immunopurified with an
O-GlcNAc-specific antibody and stringently washed, and the O-GlcNAc-
containing proteins were specifically eluted with free GlcNAc. The resulting
proteins were separated on two-dimensional gels and visualized by silver
staining. pI, isoelectric point; MW, molecular weight.
From Wells et al. (2001) Science 291, 2376-8.

36. • Jensen, O., N (2004) Modification-specific proteomics:
Characterization of post-translational modifications by mass
spectrometry. Current Openings in bio-chemistry. 8, 33-41
• Mann, M and Jensen, O., N (2003) Proteomic analysis of post-
translational modifications. Nature Biotechnology. 21, 255-261.
• Matsubayashi, Y (2012) Recent advances in research on small
post-translationally modified peptide signals in plants. Genes to
Cells 17, 1-10.
• Ralp, A. Bradshaw and Albert, E. Stewart (1994) Analysis of
protein modifications: Recent advances in detection,
characterization and mapping. 5(1), 85-93.
• Walsh C. (2006) Posttranslational modification of proteins :
Expanding nature's inventory. Englewood, Colo.: Roberts and
Co. Publishers. xxi, 490 p. p.
• Gaston B. M. et al. (2003) S-nitrosylation signaling in cell
biology. Mol Interv. 3, 253-63.
• Jaffrey S. R. and Snyder S. H. (2001) The biotin switch method
for the detection of S-nitrosylated proteins. Sci STKE. 2001, pl1.
• Han P. and Chen C. (2008) Detergent-free biotin switch
combined with liquid chromatography/tandem mass
spectrometry in the analysis of S-nitrosylated proteins. Rapid
Commun Mass Spectrom. 22, 1137-45.
References

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