Download MBBS Post Translational Processing Lecture PPT

Post-translatonal modification.
Addition of group or deletion of parts to make a finished

protein.

--- Content provided by FirstRanker.com ---

What group--
methyl
acetyl
phospho

--- Content provided by FirstRanker.com ---

What purpose ----
targeting( some lipoprotein )
stability ( secreted glycoprotein )
function ( surface glycoprotein ).
Post-translational modification of individual

--- Content provided by FirstRanker.com ---

Aminoacids.

PHOSPHORYLATION-
Phosphorylation of serine , threonine

--- Content provided by FirstRanker.com ---

and tyrosine residue occurs by specific kinase. This is a common
signal transduction mechanism in hormone action and activation/
inactivation of enzyme e.g.- glycogen synthase and phosphorylase.

HYDROXYLATION---

--- Content provided by FirstRanker.com ---

proline and lysine in collagen undergo

hydroxylation to form hydroxoproline and hydroxylysine which are
again important in the maturation of collagen .
Modification of Amino acids.

--- Content provided by FirstRanker.com ---

CARBOXYLATION-
Carboxylation of glutamate residues

in coagulation factor like prothrombin is necessary for

--- Content provided by FirstRanker.com ---

their function.

GLYCOSYLATION-
Glycosylation occurs by addition of
oligosaccharide chains to specific amino acid residue of

--- Content provided by FirstRanker.com ---

the polypeptide and is seen in glycoproteins.
Attachment of gluose to hemoglobin in HBA1c is also an

example.
N AND C TERMINAL MODIFICATION.

--- Content provided by FirstRanker.com ---

Both formylmethionine and methionine are removed by

aminopeptidases. They are not present in most mature
proteins.

--- Content provided by FirstRanker.com ---

Large majority of eukaryotic proteins are acetylated at

the N terminal residues.

--- Content provided by FirstRanker.com ---

C terminal amino acids are also modified in many proteins.
CLEAVAGE OF NASCENT POLPEPTIDE
CHAIN

Usually the nascent proteins are larger protein than their

--- Content provided by FirstRanker.com ---

mature functional counterparts.
They are called pre-pro-proteins and undergo cleavages

to become smaller and act

--- Content provided by FirstRanker.com ---

For examples, insulin is synthesized as a much larger-pre-
pro-insulin of molecular weight 11500Da while the
mature functional insulin is about half the size.

In all 38 amino acids are removed to generate a mature

--- Content provided by FirstRanker.com ---

functional insulin molecule
Similarly, chymotrypsinogen and trypsinogen are also
converted into active chymotrypsin and trypsin by
cleavage.
TRIMMING-

--- Content provided by FirstRanker.com ---

Many proteins are originally synthesised as

much bigger molecules. They undergo proteolytic
degradation or trimming to become smaller molecules

--- Content provided by FirstRanker.com ---

which are functional Example- the formation of insulin
from preproinsulin, conversion of zymogens to active
digestive enzymes, e.g. trypsinogen to trypsin, pepsinogen
to pepsin.
PROTEIN FOLDING.

--- Content provided by FirstRanker.com ---

Unique structure of protein involves the folding of its polypeptide

chain in a characteristics three dimensional structure.

This folding is essential for the biological function of the protein.

--- Content provided by FirstRanker.com ---

CHAPERONS---
Proteins require other accessory protein called

chaperons to promote folding.

--- Content provided by FirstRanker.com ---

Chaperones are the proteins which interact with partially folded or

improperly folded nascent protein to fascilitate correct folding.

--- Content provided by FirstRanker.com ---

Function--
1.Helps in protein folding.
2.Prevent Aggregation.
Ex. Hsp in eukaryotes.

--- Content provided by FirstRanker.com ---

Protein Folding

Proper folding of protein is essential for a cell to carry outs its normal

--- Content provided by FirstRanker.com ---

cellular function.

Misfolded protein can result in a wide variety of a pathological condition.

--- Content provided by FirstRanker.com ---

Loss of Protein Function.
PROTEIN FOLDING.
These are two classes?
Hsp70 protein and chaperonins.
Hsp70--

--- Content provided by FirstRanker.com ---

The Hsp70 are called heat shock proteins

(molecular weight 70KDa) because they are more abundant in

cells stressed by heat.

--- Content provided by FirstRanker.com ---

They are found in all organisms from bacteria to human

beings.

--- Content provided by FirstRanker.com ---

These chaperones protect ptoteins which are

denatured by heat and from aggregates.

--- Content provided by FirstRanker.com ---

Chaperonins--

The Hsp60 family of proteins are referred to as

chaperonins.

--- Content provided by FirstRanker.com ---

Chaperonins usually act later along with Hsp70.
PROTEIN MISFOLDING DISEASES.

Protein misfolding disease can be classified in to two

--- Content provided by FirstRanker.com ---

categories.

Diseases caused due to the misfolding or degradation of

--- Content provided by FirstRanker.com ---

misfolded protein.

Disease caused due to accumulation of misfolded protein.

Reason for protein misfolding---

--- Content provided by FirstRanker.com ---

Mutation.

Premature termination of translation.

--- Content provided by FirstRanker.com ---

Fault in post- translational modification.
DISEASE CAUSED DUE TO THE ACCUMULATION
OF MISFOLDED PROTEIN.

PRION DISEASES--

--- Content provided by FirstRanker.com ---

The prion diseases are neuro-degenerative caused

by misfolded protein.

--- Content provided by FirstRanker.com ---

? They are characterised by dementia, loss of

coordination and encephalitis leading to fatal
outcome.
Prion diseases.

--- Content provided by FirstRanker.com ---

Diseases Due to misfolded protein.
DISEASE

PROTEIN INVOLVED.

--- Content provided by FirstRanker.com ---

Alzheimer's disease

Amyloid Beta ? peptide.

Spongiform encephalopaties.

--- Content provided by FirstRanker.com ---

Prion protein

Huntington disease

--- Content provided by FirstRanker.com ---

Huntington protein.
Alzheimer's Disease.
Spongiform encephalitis.

These diseases are also called spongiform encephalitis

--- Content provided by FirstRanker.com ---

because they produce vacuolar or spongiform
changes in brain.

The best known examples is mad-cow disease or
bovine spongiform encephalitis.

--- Content provided by FirstRanker.com ---

Prion infected Brain of a cattle.
Prion disease.

Creutzfeldt disease is an examples in humans.
The causative agent is a prion protein---PrP,

--- Content provided by FirstRanker.com ---

(moleculer weight 28 Kda) coded by PrP gene on
chromosome 20.
Prion diseases may manifest as genetic, infectious and
sporadic diseases.
PROTEIN TARGETING.

--- Content provided by FirstRanker.com ---

PROTEIN TARGETING-
PROTEIN FOR EXTERNAL SECRETION

The process is also called

--- Content provided by FirstRanker.com ---

as "protein sorting'' or ``protein localization''. The
secreted proteins, plasma membrane integral proteins,
lysosomal enzymes and membrane proteins of ER are
synthesized on rough endoplasmic reticulum by

--- Content provided by FirstRanker.com ---

membrane bound polyribosomes. The newly synthesized
protein is then delivered to the destined compartment.
Blobel and sabatini proposed the signal hypothesis to
explain the different destination of proteins. Guenter
Blobel was awarded Nobel Price in 1999.

--- Content provided by FirstRanker.com ---

Protein targeting.
Protein targeting or protein sorting is the mechanism by

which a cell transport to the appropriate positions in the

--- Content provided by FirstRanker.com ---

cell or outside of it.

Protein targeting is necessory for protein that are

destined to work outside the cytoplasm.

--- Content provided by FirstRanker.com ---

The delivery process is carried out based on information

contained in the protein itself.

--- Content provided by FirstRanker.com ---

Correct sorting is crucial for the cell, errors can lead to

disease.

Synthesized protein is transferred to an SRP receptor on

--- Content provided by FirstRanker.com ---

endoplasmic reticulum, nascent protein is inserted into

translocation complex.
Targeting signal.

--- Content provided by FirstRanker.com ---

Targeting signal are the piece of information that enable

the cellular transport machinery to correctly position a
protein inside or outside the cell.

--- Content provided by FirstRanker.com ---

This information is contained in the polypeptide chain or

in the folded protein.

--- Content provided by FirstRanker.com ---

In abscence of targeting signal, a protein will remain in the

cytoplasm.
Protein targeting.

--- Content provided by FirstRanker.com ---

Protein has to correctly localised to perform proper

function.

Receptor---plasma membrane.

--- Content provided by FirstRanker.com ---

DNA polymerase--nucleus.

Catalase-----peroxisomes.

--- Content provided by FirstRanker.com ---

Insulin-------outside.
All protein begins to be synthesized on cytosolic

ribosomes.

--- Content provided by FirstRanker.com ---

Sorting or translocation can occur

Co- tranlational.

Post-translational.

--- Content provided by FirstRanker.com ---

If protein is for cytosolic function, the synthesis will be

finished on free ribosomes and the peptide is released
into the cytosol.

--- Content provided by FirstRanker.com ---

Protein targeting.

The nascent protein is passed through the membrane into the

channels of ER. Then protein synthesis is completed, and the

--- Content provided by FirstRanker.com ---

protein molecule is now inside the endoplasmic membrane. As
the nascent protein is traversing the inner membrane of ER,
carbohydrate moieties are added at particular regions by
specific enzymes; this is called co-translational glycosylation.

--- Content provided by FirstRanker.com ---

CORRECT ADDRESS of DESTINATION is LABELED
The protiens carry an "address" that is specific for its correct

destination inside the cell. This is present in the carboxy
terminal end of proteins. Diseases due to defective protein

--- Content provided by FirstRanker.com ---

targeting.
Protein targeting.
Protein Targeting
Zellweger syndrome is due to defective oxidation of very long chain

--- Content provided by FirstRanker.com ---

fatty acids (VLCFA). Here the correct "address" is not printed on

the protein packet; so that it could not be delivered to the correct

location. Peroxisomal enzymes are produced; but their entry into

--- Content provided by FirstRanker.com ---

peroxisomal is denied. This leads to insufficient oxidation of VLCFA.

Accumulation of VLCFA in CNS causes neurological impairment and

--- Content provided by FirstRanker.com ---

death in childhood.

Another example is primary hyperoxaluria, which causes

kidney stones at an early age. The defect is due to protein trageting

--- Content provided by FirstRanker.com ---

defect and the enzyme alanine glyoxylate amino transferase seen in

mitochondria, instead of its normal peroxisomal location.

--- Content provided by FirstRanker.com ---

Iysosomes cell diseases due to non-entry of normal enzymes into

Iysosomes. Mannose-6-phosphate is the marker to target enzymes

to Iysosomes;this is absent.

--- Content provided by FirstRanker.com ---

MITOCHONDRIAL DNA and RNA.

Some of mitochondrial protein synthesis is under the control

--- Content provided by FirstRanker.com ---

of mitochondrial DNA;

but important proteins of the outer membrane of the

--- Content provided by FirstRanker.com ---

mitochondria are synthesized under the influence of nuclear
DNA.

Shows that mitochondria are similar to bacteria more than

--- Content provided by FirstRanker.com ---

mammalian cells.

This fact supports the theory that mitochondria are derived

from prokaryotes symbiotically adapted to multicellular

--- Content provided by FirstRanker.com ---

organisms.
Maternal inheritance:

Since, the mitochondria are inherited cytoplasmically,

--- Content provided by FirstRanker.com ---

the mtDNA is inherited from the mother.


Mother transmits mtDNA through oocyte.

--- Content provided by FirstRanker.com ---

There are hunderds of copies of mtDNA in each cell

(nuclear DNA has only 2 copies).
During cell division, mtDNA replicates and they segregate

--- Content provided by FirstRanker.com ---

to the daughter cells.

If a mutation occurs in mtDNA, the daughter cells may

inherit the mutant or normal mtDNA.

--- Content provided by FirstRanker.com ---

Heteroplasmy is defined as the presence of normal and

mutant mtDNA in different proportions in different cells.
Defects in mitochondrial genome will lead to mitochondrial

--- Content provided by FirstRanker.com ---

myopathies.

Leber`s hereditary optic neuropathy is caused by a single base

--- Content provided by FirstRanker.com ---

mutation which alters one argrinine to histidine in the NADH
Coenzyme Q reductase. OXPHOS (oxidative
phosphorylation).
OXPHOS DISEASES

--- Content provided by FirstRanker.com ---

Syndrome

Features

Leber`s Hereditary

--- Content provided by FirstRanker.com ---

Complex l defect; blindness,cardiac

Neuropathy(LHON)

--- Content provided by FirstRanker.com ---

conduction defects

Myoclonic epilepsy ragged

Myoclonic epilepsy, myopathy,

--- Content provided by FirstRanker.com ---

Red fiber diseases (MERRF)

dementia

--- Content provided by FirstRanker.com ---

Leigh`s syndrome

Complex l defect ; movement
disorders
GENOME AND PROTEOME.

--- Content provided by FirstRanker.com ---

All the DNA contained in an organism or a cell which

includes both the chrosomes within the nucleus and the
DNA in mitochondria----GENOME.

--- Content provided by FirstRanker.com ---

PROTEOME--Is the some of all proteins expressed by

the genome of an organism.