Post-Translational Modifications

11/13/2012 MOLECUAR BIOLOGY 1

 Translation is the synthesis of protein from an
mRNA template.
 This process involves several key molecules
including:
1. mRNA
2. Ribosome
3. tRNA
4. Release Factor


 Initiation
 Elongation
 Termination


 Peptide chain undergoes folding
 Some amino acids might be changed
 Carbohydrates or lipids can be added
 Peptide can be activated by addition or removal of
some residue (acetate, phosphate, methyl etc.)


 Changes in the Hydrogen bond proclivity which
results in secondary and tertiary structures
 Some of the proteins might remain in cytosol while
others are transported across the membrane or
even imported into cellular organelles
(mitochondria or chloroplasts) to accomplish their
functions


 The chemical modification of a protein after its
translation is known as Post-Translational
Modification.


 Play a crucial role in generating the heterogeneity in
proteins.
 Help in utilizing identical proteins for different
cellular functions in different cell types.
 Regulation of particular protein sequence behavior
in most of the eukaryotic organisms.


 Play an important part in modifying the end product
of expression.
 Contribute towards biological processes and
diseased conditions.
 Translocation of proteins across biological
membranes.


 Trimming
 Covalent Modification
 Ubiquitination


 Removal of a part of the translated sequence.
 Proteases Protein activation.


 Phosphorylation
 Glycosylation
 Hydroxylation
 Carboxylation
 Biotinylation
 Acetylation


 Methylation
 Alkylation
 Glutamylation
 Lipoylation
 Sulfation


 Phosphorylation
 The addition of a phosphate (PO4) group to a
protein or a small molecule.
 Can occur on Serine, Threonine, Tyrosine.


 Glycosylation
 The addition of saccharide to a protein or a lipid
molecule.
 N-Linked Glycosylation
• Amide nitrogen of Asparagine
 O-Linked Glycosylation
• Hydroxyl oxygen of Serine and Therionine.


 Hydroxylation
 The addition of hydroxyl group to proline of
protein.

 Carboxylation
 The addition of carboxyl group to glutamate.


 Biotinylation
 The addition of biotin to protein or nucleic acid.
 Acetylation
 The addition of an acetyl group, usually at the N-
terminus of the protein.


 Methylation
 The addition of a methyl group, usually at lysine
or arginine residues.

 Alkylation
 The addition of an alkyl group (e.g. methyl, ethyl).


 Glutamylation
 Covalent linkage of glutamic acid residues to
tubulin and some other
 Lipoylation
 The attachment of a lipoate functionality
 Sulfation
 The addition of a sulfate group to a tyrosine.


 Highly specific degradation of protein can be
achieved through the addition of one to
several ubiquitin molecules to a target
protein. The process is called Ubiquitination.


 These are particularly important for the study of
heart disease, cancer, neurodegenerative diseases
and diabetes.
 These are key mechanisms to increase proteomic
diversity.


 A protein synthesis inhibitor is a substance
that stops or slows the growth or
proliferation of cells by disrupting the
processes that lead directly to the generation
of new protein.


 In general, antibiotics are biochemically or
fungally produced substances that inhibit the
growth of other organisms. Most antibiotics,
like many pharmaceuticals, block translation
in protein synthesis.


 These substances are effective because they
take advantage of the tremendous
complexity involved in the synthesis of
proteins.


 Puromycin
 Streptomycin
 Erythromycin
 Tetracyclin
 Penicillin
 Chloramphenicol
 Rifampin
 Fusidic Acid
 Thiostrepton

 Puromycin
 Inhibits protein synthesis at translation by
prematurely terminating a peptide chain.
 In simple terms, the part of puromycin that
resembles an aminoacyl end of tRNA can bind to
the A site of a ribosome.


Streptomycin
Depending on its
concentration, streptomycin can affect
bacterial cells in two ways.
Low concentration
At low concentrations, it induces mRNA
misreading, so that improper amino acids are
incorporated into the polypeptide.


 High concentration
 At high concentrations, 70s nonproductive
ribosome: mRNA complexes accumulate,
preventing formation of active initiation
complexes with new mRNA.


 Once a polypeptide chain is assembled, it still
requires two major "finishing steps" before it
becomes functional.
 Chemical modification
 Folding


 Chemical modification involves three steps:
 modification of amino acid residues into
other types,
 addition of organic units (such as sugars or
lipids) to specific amino acids,
 enzymatic cleavage of one or more amino
acids from a region of the polypeptide chain.


 The abundance of collagen in the
extracellular structures of humans and other
mammals makes disorders of collagen
deposition.
 Atherosclerosis
 Fibrosis
 Progressive Systemic Sclerosis (Scleroderma)


 Atherosclerosis
 a disease involving stiffening of the arteries, is
related to an over-deposition of collagen
 Fibrosis
 A disease involving hardening of the tissues, is
related to excessive collagen synthesis.


 Progressive Systemic Sclerosis
(Scleroderma)
 A disease of the vascular and immune
systems, and a severe connective tissue disorder.


Post-Translational Modifications

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