Lecture 5 - Post Transcriptional Modifications and Processing of Eukaryotic RNA | Molecular Biology (DNA) by ILLL, DU - Biotechnology Engineering (BT) PDF Download

 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