3. POST-TRANSLATIONAL MODIFICATION
● key mechanisms to increase proteomic diversity
● It is the chemical modification of protein
after its translation.
● OCCURANCE ON AMINO ACID SIDE
CHAINS OR AT THE C/N-TERMINI
EXAMPLE: Prohormone------->Hormone
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i) Covalent addition of functional
group or protein
ii) Proteolytic cleavage of
regulatory subunits
iii) Degradation of entire protein
6. 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
EXAMPLE: *mTOR PATHWAY
*ADP + P----->ATP(oxidative phosphorylation)
*O-Phosphorylation at Serine residue.
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7. 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
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9. Ubiquitination
● Reversible PTM, first studied by G. Goldstein in 1975.
● Ubiquitin is a small regulatory protein
● attached to the proteins and label them for destruction.
● Polyubiqitination
● Effects in cell cycle regulation, control of proliferation and differentiation,
programmed cell death (apoptosis), DNA repair, immune and inflammatory
processes and organelle biogenesis 9
11. S-Nitrosylation
● Nitrosyl (NO) group is added to the protein.
● the covalent attachment of a nitric oxide moiety to a cysteine thiol
● NO a chemical messenger that reacts with free cysteine residues to form S-
nitrothiols.
● Used by cells to stabilize proteins, regulate gene expression.
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12. Methylation
● Addition of methyl group to a protein.
● Usually at lysine or arginine residues.
● Primary methyl donor is S-adenosylmethionine (SAM)
● Enzyme for this is methyltransferase
● N-methylation is irreversible
● Methylation of lysine residues in histones in DNA is important regulator of
chromatin structure.
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13. N-Acetylation
● Addition of acetyl group to the nitrogen.
● Histones are acetylated on lysine residues in the N-terminal tail as a part of gene
regulation.
● Degree of acetylation affects the state of nucleosome aggregation.
● Non-acetylated histones - condensed chromatin
● Acetylated histones - less condensed chromatin
● Involved in regulation of transcription factors, effector proteins, molecular
chaperons and cytoskeletal proteins. 13
14. Identification of modifications
• Mass spectrometry
• HPLC analysis
• Antibody cross-reactivity – e.g., antibody against phosphotyrosine
• Polyacrylamide gel electrophoresis (PAGE)
• Biotin switch assay (for S-nitrosylation) -
● All free cysteines are blocked.
● All remaining cysteines (presumably only those that are denitrosylated) are
denitrosylated.
● The now-free thiol groups are then biotinylated.
● Biotinylated proteins are detected by SDS-PAGE and western blot analysis
or mass spectrometry. 14
15. TOOLS & SOFTWARE
List of software for visualization of proteins and their PTMs
● PyMOL – introduce a set of common PTM's into
protein models
● AWESOME – Interactive tool to see the role of
single nucleotide polymorphisms to PTM's
● Chimera – Interactive Database to visualize
molecules
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16. ➔ different post-translational modifications exponentially
increases the complexity of the proteome relative to
both the transcriptome and genome.
➔ While the genome
comprises 20,000 to
25,000 genes, the
proteome is estimated to
encompass over 1 million
proteins.
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18. ACKNOWLEDGMENT
● Dr B E PRADEEP sir - for giving me the opportunity to present
on this topic.
● Family and friends - for helping me and providing me with key
points to improve my slides
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