Page 1
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 1
Molecular Biology
Lesson: Post translational modification
Lesson Developer: Dr. Jasvinder Kaur and Dr. Shailly Anand
College/Dept: Gargi College, Zoology Department
University of Delhi
Page 2
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 1
Molecular Biology
Lesson: Post translational modification
Lesson Developer: Dr. Jasvinder Kaur and Dr. Shailly Anand
College/Dept: Gargi College, Zoology Department
University of Delhi
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 2
Table of Contents
? Introduction
? Post-translational modifications
? Phosphorylation
? Glycosylation
? Ubiquitination
? Methylation
? Acetylation
? N-nitrosylation
? Lipidation
? Proteolysis
? SUMOylation
? Role of chaperones in normal protein folding and protection
? Summary
? Exercise
? Glossary
? References/ Bibliography
Page 3
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 1
Molecular Biology
Lesson: Post translational modification
Lesson Developer: Dr. Jasvinder Kaur and Dr. Shailly Anand
College/Dept: Gargi College, Zoology Department
University of Delhi
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 2
Table of Contents
? Introduction
? Post-translational modifications
? Phosphorylation
? Glycosylation
? Ubiquitination
? Methylation
? Acetylation
? N-nitrosylation
? Lipidation
? Proteolysis
? SUMOylation
? Role of chaperones in normal protein folding and protection
? Summary
? Exercise
? Glossary
? References/ Bibliography
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 3
Introduction
The human genome is estimated to have around
20,000-25,000 genes and the human proteome
is expected to be much more complex. This
complexity is on account of a wide range of
modifications occurring at the transcriptional
level, during protein synthesis and even beyond.
Polypeptides can be modified while they are still
being synthesized in the rough endoplasmic
reticulum (co-translational modification) or after
the synthesis is complete (post-translational
modification).
Source: Author
Protein post-translational modification (PTM) is a critical step that follows protein
biosynthesis in eukaryotes. Through the process of translation the ribosomes string together
a set of amino acids in a particular order to form polypeptides. These are then modified in
different ways to make fully functional proteins. This way, the functional range of the
proteome is widened beyond imagination by covalent addition of biochemical functional
groups or by trimming certain lengths of the translated sequence. These modifications
range from folding of the polypeptide into proper conformations by chaperones, addition of
certain functional groups to the translated protein and proteolytic cleavage of regulatory
subunits (Figure 1). PTMs also involve processing in which appropriate tags are added to the
protein for its trafficking within the correct subcellular compartment or extracellular
location. Post-translational modifications play a critical role in all aspects of normal cellular
functioning such as regulating protein activity, protein localization and their interaction with
other biomolecules. Thus, PTM constitutes a very important aspect to be studied in detail
which may ultimately contribute towards detection and cure of diseases. PTMs are important
for the study of cancer, diabetes, heart and neurodegenerative diseases.
Post-translational modifications
The polypeptides formed just after translation must be folded properly to acquire fully
functional three-dimensional conformation.
Page 4
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 1
Molecular Biology
Lesson: Post translational modification
Lesson Developer: Dr. Jasvinder Kaur and Dr. Shailly Anand
College/Dept: Gargi College, Zoology Department
University of Delhi
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 2
Table of Contents
? Introduction
? Post-translational modifications
? Phosphorylation
? Glycosylation
? Ubiquitination
? Methylation
? Acetylation
? N-nitrosylation
? Lipidation
? Proteolysis
? SUMOylation
? Role of chaperones in normal protein folding and protection
? Summary
? Exercise
? Glossary
? References/ Bibliography
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 3
Introduction
The human genome is estimated to have around
20,000-25,000 genes and the human proteome
is expected to be much more complex. This
complexity is on account of a wide range of
modifications occurring at the transcriptional
level, during protein synthesis and even beyond.
Polypeptides can be modified while they are still
being synthesized in the rough endoplasmic
reticulum (co-translational modification) or after
the synthesis is complete (post-translational
modification).
Source: Author
Protein post-translational modification (PTM) is a critical step that follows protein
biosynthesis in eukaryotes. Through the process of translation the ribosomes string together
a set of amino acids in a particular order to form polypeptides. These are then modified in
different ways to make fully functional proteins. This way, the functional range of the
proteome is widened beyond imagination by covalent addition of biochemical functional
groups or by trimming certain lengths of the translated sequence. These modifications
range from folding of the polypeptide into proper conformations by chaperones, addition of
certain functional groups to the translated protein and proteolytic cleavage of regulatory
subunits (Figure 1). PTMs also involve processing in which appropriate tags are added to the
protein for its trafficking within the correct subcellular compartment or extracellular
location. Post-translational modifications play a critical role in all aspects of normal cellular
functioning such as regulating protein activity, protein localization and their interaction with
other biomolecules. Thus, PTM constitutes a very important aspect to be studied in detail
which may ultimately contribute towards detection and cure of diseases. PTMs are important
for the study of cancer, diabetes, heart and neurodegenerative diseases.
Post-translational modifications
The polypeptides formed just after translation must be folded properly to acquire fully
functional three-dimensional conformation.
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 4
Figure 1: Post-translational modification of proteins occurs through
various mechanisms. For example, after a protein is translated, carbohydrate, small
ubiquitin related modifier (SUMO) or phosphate moieties can be added to the protein or can
be proteolyticaly modified.
Source: Author
Table 1: Protein modifications, their target sites and the cellular process
they may affect.
Modification Occurs at Affects
Truncation Many Activation
Glycosylation Thr, Asn, Ser Protein activity
Sulfation Tyr Protein-protein interaction
Phosphorylation Tyr, Ser, Thr Activation, signaling
Methylation His, Arg, Glu, Lys Chemotaxis, Protein repair
Palmitoylation Cys Membrane association
Ubiquitylation Lys Degradation/other
Acetylation Lys, N-terminus Gene expression
Prenylation Cys Oncogenesis, signaling
Amidation C-terminus Bioactive peptides
Hydroxylation Asp, Lys, Pro, Phe Collagen synthesis, chemotaxis
Page 5
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 1
Molecular Biology
Lesson: Post translational modification
Lesson Developer: Dr. Jasvinder Kaur and Dr. Shailly Anand
College/Dept: Gargi College, Zoology Department
University of Delhi
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 2
Table of Contents
? Introduction
? Post-translational modifications
? Phosphorylation
? Glycosylation
? Ubiquitination
? Methylation
? Acetylation
? N-nitrosylation
? Lipidation
? Proteolysis
? SUMOylation
? Role of chaperones in normal protein folding and protection
? Summary
? Exercise
? Glossary
? References/ Bibliography
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 3
Introduction
The human genome is estimated to have around
20,000-25,000 genes and the human proteome
is expected to be much more complex. This
complexity is on account of a wide range of
modifications occurring at the transcriptional
level, during protein synthesis and even beyond.
Polypeptides can be modified while they are still
being synthesized in the rough endoplasmic
reticulum (co-translational modification) or after
the synthesis is complete (post-translational
modification).
Source: Author
Protein post-translational modification (PTM) is a critical step that follows protein
biosynthesis in eukaryotes. Through the process of translation the ribosomes string together
a set of amino acids in a particular order to form polypeptides. These are then modified in
different ways to make fully functional proteins. This way, the functional range of the
proteome is widened beyond imagination by covalent addition of biochemical functional
groups or by trimming certain lengths of the translated sequence. These modifications
range from folding of the polypeptide into proper conformations by chaperones, addition of
certain functional groups to the translated protein and proteolytic cleavage of regulatory
subunits (Figure 1). PTMs also involve processing in which appropriate tags are added to the
protein for its trafficking within the correct subcellular compartment or extracellular
location. Post-translational modifications play a critical role in all aspects of normal cellular
functioning such as regulating protein activity, protein localization and their interaction with
other biomolecules. Thus, PTM constitutes a very important aspect to be studied in detail
which may ultimately contribute towards detection and cure of diseases. PTMs are important
for the study of cancer, diabetes, heart and neurodegenerative diseases.
Post-translational modifications
The polypeptides formed just after translation must be folded properly to acquire fully
functional three-dimensional conformation.
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 4
Figure 1: Post-translational modification of proteins occurs through
various mechanisms. For example, after a protein is translated, carbohydrate, small
ubiquitin related modifier (SUMO) or phosphate moieties can be added to the protein or can
be proteolyticaly modified.
Source: Author
Table 1: Protein modifications, their target sites and the cellular process
they may affect.
Modification Occurs at Affects
Truncation Many Activation
Glycosylation Thr, Asn, Ser Protein activity
Sulfation Tyr Protein-protein interaction
Phosphorylation Tyr, Ser, Thr Activation, signaling
Methylation His, Arg, Glu, Lys Chemotaxis, Protein repair
Palmitoylation Cys Membrane association
Ubiquitylation Lys Degradation/other
Acetylation Lys, N-terminus Gene expression
Prenylation Cys Oncogenesis, signaling
Amidation C-terminus Bioactive peptides
Hydroxylation Asp, Lys, Pro, Phe Collagen synthesis, chemotaxis
Post translational modifications
Institute of Lifelong Learning, University of Delhi Page 5
Myristoylation Cys Membrane association
Some of the proteins need to be cleaved properly for correct localization within the cell and
activation of protein. In addition, they are also modified by the covalent addition of
biochemical groups. Post-translational modifications are mediated most commonly by
enzymatic activity. It is estimated that 5% of the proteome is employed in carrying out 200
types of PTMs (Table 1). Phosphatases can remove phosphate groups, kinases can add
phosphate groups, ligases add functional moieties, lipids or proteins can be added or
removed from amino acid side chains, proteases can cleave peptide bonds, disulfide bonds
can be formed between sulfhydryl groups (-SH) catalyzed by thiol-disulfide oxidoreductases.
After the polypeptide is adequately modified, the functional protein is then transported
inside or outside the cell according to its fate decided by signal peptide. Polypeptides are
often tagged with a short stretch of amino acids at the N-terminal end to mark their fate
into various compartments within or out of the cell. Additionally chaperones act as catalysts
to fold the polypeptide into higher order conformations. PTMs can occur at any point in the
life-history of a protein. A protein can be folded and stabilized before they can be targeted
for localization to a specific organelle (eg. Mitochondria, nucleus, lysosome). Second type of
modification occurs after proteins are folded and localized to their respective compartment;
their activities can then be modified or regulated by the addition or removal of functional
groups. Post translational modifications can be reversible or irreversible. Table 2
summarizes the location of these modifications in a cell.
Table 2: Post-translational modifications and their respective locations
within the cell
Location Modifications
Cytoplasm Proteolysis, removal of formyl methioine, Acetylation,
Myristoylization, O-glycosylation of N-acetylglucosamine
(GlcNAc), Palmitoyl addition, Virus processing
Mitochondria and
Chloroplast
Signal peptide cleavage
Endoplasmic reticulum Signal peptide cleavage, glycosylation of Asn (N-
glycosylation), Post carboxylation and hydroxylation
(Pro and Lys), Disulfide bond formation, palmitoyl and
glycosyl-phosphotidylinositolization
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