post translation modification of protein

1. DEPARTMENT OF PLANT BIOTECHNOLOGY
BANARAS HINDU UNIVERSITY
POST-TRANSLATIONAL
MODIFICATION OF PROTEIN
SUBMITTED TO:- Dr. ASHOK MURYA
SUBMITTED BY:- Mr. SIDDHANT
ROLL NO. :-17PBT022

2. POST-TRANSLATIONAL MODIFICATION
 Post translational modification (PTM) is the
chemical modification of a protein after its
translation.
OR
 The chemical modifications that take place at
certain amino acid residues after the protein is
synthesized by translation are known as post-
translational modifications.
These are essential for normal functioning of
the protein.
PTMS occur mostly in E.R and golgi apparatus.

3. Why PTM is necessary???
Stability of Protein
Biochemical Activity (Activity
Regulation)
Protein Targeting(Protein
Localization)
Protein Signaling(Protein-Protein
Interaction, cascade
amplification).

5. Modification Involving Peptide Bonds
1
2
5
• Peptide Bonds Cleavage
• Peptide Bond Isomerization

6. Modification Involving Peptide Bonds
Cleavage(Limited Proteolysis)
 Specific and well-regulated
 Enzymatic and Non-Enzymatic
Examples:
Removal of signal leader peptide by signal peptidase
 Precursor protein → mature protein (Insulin)
Zymogen → active enzyme
Trypsinogen → Trypsin
Prohormone → Hormone

7. Modification Involving Peptide Bond
Isomerization (Intramolecular)
 Ser → esters
 Cys → thioesters
 Asp or Asn → isoaspartate
 Prolyl peptide cis-trans isomerization by prolyl isomerase

8. Modification of
amino acids
8

10. 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

11. Glycosylation
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.

12. 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.
 Involved in regulation of transcription
factors, effector proteins, molecular
chaperons and cytoskeletal proteins.
 Methionine aminopeptidase (MAP) is an
enzyme responsible for N-terminal acetylation

13. Lipidation
 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.

14. 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.

15. Ubiquitination
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.

16. Ubiquitin Cycle

17. POST TRANSLATION MODIFICATION
PROTEIN
FOLDING
 Physical process leading from an unfolded
polypeptide chain to a functional protein with
a definite structure.
 Minimizing the number of hydrophobic side-
chains exposed to water is an important
driving force.
 The native state is the most stably folded
form.

18. PROTEIN FOLDING
 The folding process depends on the solvent ,
the salts concentration , the pH, the
temperature and molecular chaperones.
 Chaperones are proteins that facilitate
the folding of other proteins without
being part of assembled complex .

19. In vivo Protein folding in absence or presence
of Chaperones

20. POST TRANSLATION MODIFICATION
SUBUNIT
AGGREGATION
 Multimeric proteins are assembled in the ER.
 Some folded protein chains (subunits)
must aggregate with other subunits to
form quaternary structure.
 Such multi-subunit proteins include
many of the most important enzymes
and transport proteins in the cell.

21. s Haemoglobin A

22. Protein splicing is an intramolecular reaction of a
particular protein in which an internal protein
segment (called an intein) is removed from a
precursor protein with a ligation of C-terminal and N-
terminal external proteins (called exteins) on both
sides.
No coenzymes or sources of metabolic energy.
Involves bond rearrangements rather than
bond cleavage followed by re-synthesis.
 Converts Inactive protein precursor to
biologically active protein.
PROTEIN SPLICING

23. An intein is a segment of a
protein that is able to excise
itself and join the remaining
portions( the exins) with
peptide bond.
Found in Bacteria eukarotes,
Archaea and Viruses.
What the INTEINS are???

24. Mechanism of Protein Splicing

25. THANKYOU