Prein
,Q. Discuss the protein misfolding & various diseases related to it.
PROTEIN FOLDING
Proteins are conformationally dynamic molecule that can fold into functionally
competent conformation. Auxillary Proteins assist Protein Folding, they are called
Chaperones.
Properties of Chaperone Proteins
Present in a wide range of species from bacteria to humans
Many are so-called Heat Shock Proteins (Hsp)
Are inducible by conditions that cause unfolding of newly synthesized proteins (e.g.
elevated temperature and various chemicals)
They bind to predominantly hydrophobic regions of unfolded proteins and prevent
their aggregation
They act in part as a quality control or editing mechanism for detecting misfolded or
otherwise defective proteins
Most chaperones show associated ATPase activity.
Molecular Chaperones are :
HSP 70
HSP 90
HSP 40 [Cochaperone]
BiP [Immunoglobulin heavy chain binding protein]
Glucose Regulated Protein [GRP-94]
Calreticulin
Calnexin.
Enzymes assist folding are :
Protein Disulphide Isomerase
Peptidyl Prolyl Isomerase
Chaperonins
HSP 60 family of chaperones, sometimes called chaperonins
They form complex barrel-like structures in which an unfolded protein is retained,
giving it time and suitable conditions in which to fold properly
For example, mtGroEL chaperonin.
,Steps of ERAD (Endoplasmic Reticulum Associated Degradation of Proteins) :
A target protein which is misfolded undergoes retrograde transport through the ER
(Retrotranslocation or dislocation) membrane into the cytosol
It is subjected to polyubiquitination
Then enters a proteasome, inside which it is degraded to small peptides that exit and
may have several fates.
proteins that helps in the retrotranslocation are :
Sec61 (Translocon)
Degradation in ER protein1 (derlin 1)
ERAD E3 ligases
Hrd1
Doa10
Ubiquitin
Key molecule in protein degradation
Small protein with 76 Amino Acids
Highly conserved protein
Attachment of ubiquitin to protein to be degraded is called Kiss of death
Ubiquitin bind to amino group of Lysine of the target protein hence it is a
Pseudopeptide or isopeptide bond or non peptide bond
Minimum of four ubiquitin molecules must be attached to commit target molecule to
degradation
N end rule of ubiquitin binding
Ubiquitin bind to proteins with PEST [Proline, Glutamic Acid, Serine and Threonine]
sequence in the amino terminal.
Proteasome
Ubiquitinated proteins are degraded in Proteasome
Located in the Cytosol
Large cylindrical structure composed of 50 sub-units
This is an ATP dependent process.
, PROTEIN MISFOLDING DISORDER
1. AMYLOIDOSIS
caused by the extracellular deposition of insoluble polymeric protein in tissues and
organs.
Amyloid Fibrils
X-ray crystallography and infrared spectroscopy demonstrate a characteristic cross-
pleated sheet conformation.
Congo red staining shows apple-green birefringence under polarized light.
By electron microscopy amyloid is seen to be made up largely of continuous, non
branching fibrils.
Protein misfolding results in Amyloidosis
The proteins that form amyloid fall into two general categories:
Increased production of normal proteins that have an inherent tendency to fold
improperly, associate and form fibrils. Examples :
- SAA is synthesised by the liver cells under the influence of cytokines such as IL-6 and
IL-1 that are increased during long standing inflammation leads to AA Amyloid
- Immunoglobulin light chain synthesized by the plasma cells
increased in Monoclonal B lymphocyte proliferation results in AL Amyloid
In Alzehimer disease, β amyloid an extracellular peptide containing 40-42 amino
acid residues gets accumulated. This is neurotoxic, and is the central pathogenic
event leading to the cognitive impairment characteristic of the disease.
The Aβ that is deposited in the brain in Alzheimer disease is derived by proteolytic
cleavages from the larger amyloid precursor protein—a single transmembrane
protein expressed on the cell surface in the brain and other tissues.
The Aβ peptides aggregate, generating the amyloid that is found in the brain
parenchyma and around blood vessels.
A second biological factor involved in the development of Alzheimer disease is the
accumulation of neurofibrillary tangles inside neurons.
,Q. Discuss the protein misfolding & various diseases related to it.
PROTEIN FOLDING
Proteins are conformationally dynamic molecule that can fold into functionally
competent conformation. Auxillary Proteins assist Protein Folding, they are called
Chaperones.
Properties of Chaperone Proteins
Present in a wide range of species from bacteria to humans
Many are so-called Heat Shock Proteins (Hsp)
Are inducible by conditions that cause unfolding of newly synthesized proteins (e.g.
elevated temperature and various chemicals)
They bind to predominantly hydrophobic regions of unfolded proteins and prevent
their aggregation
They act in part as a quality control or editing mechanism for detecting misfolded or
otherwise defective proteins
Most chaperones show associated ATPase activity.
Molecular Chaperones are :
HSP 70
HSP 90
HSP 40 [Cochaperone]
BiP [Immunoglobulin heavy chain binding protein]
Glucose Regulated Protein [GRP-94]
Calreticulin
Calnexin.
Enzymes assist folding are :
Protein Disulphide Isomerase
Peptidyl Prolyl Isomerase
Chaperonins
HSP 60 family of chaperones, sometimes called chaperonins
They form complex barrel-like structures in which an unfolded protein is retained,
giving it time and suitable conditions in which to fold properly
For example, mtGroEL chaperonin.
,Steps of ERAD (Endoplasmic Reticulum Associated Degradation of Proteins) :
A target protein which is misfolded undergoes retrograde transport through the ER
(Retrotranslocation or dislocation) membrane into the cytosol
It is subjected to polyubiquitination
Then enters a proteasome, inside which it is degraded to small peptides that exit and
may have several fates.
proteins that helps in the retrotranslocation are :
Sec61 (Translocon)
Degradation in ER protein1 (derlin 1)
ERAD E3 ligases
Hrd1
Doa10
Ubiquitin
Key molecule in protein degradation
Small protein with 76 Amino Acids
Highly conserved protein
Attachment of ubiquitin to protein to be degraded is called Kiss of death
Ubiquitin bind to amino group of Lysine of the target protein hence it is a
Pseudopeptide or isopeptide bond or non peptide bond
Minimum of four ubiquitin molecules must be attached to commit target molecule to
degradation
N end rule of ubiquitin binding
Ubiquitin bind to proteins with PEST [Proline, Glutamic Acid, Serine and Threonine]
sequence in the amino terminal.
Proteasome
Ubiquitinated proteins are degraded in Proteasome
Located in the Cytosol
Large cylindrical structure composed of 50 sub-units
This is an ATP dependent process.
, PROTEIN MISFOLDING DISORDER
1. AMYLOIDOSIS
caused by the extracellular deposition of insoluble polymeric protein in tissues and
organs.
Amyloid Fibrils
X-ray crystallography and infrared spectroscopy demonstrate a characteristic cross-
pleated sheet conformation.
Congo red staining shows apple-green birefringence under polarized light.
By electron microscopy amyloid is seen to be made up largely of continuous, non
branching fibrils.
Protein misfolding results in Amyloidosis
The proteins that form amyloid fall into two general categories:
Increased production of normal proteins that have an inherent tendency to fold
improperly, associate and form fibrils. Examples :
- SAA is synthesised by the liver cells under the influence of cytokines such as IL-6 and
IL-1 that are increased during long standing inflammation leads to AA Amyloid
- Immunoglobulin light chain synthesized by the plasma cells
increased in Monoclonal B lymphocyte proliferation results in AL Amyloid
In Alzehimer disease, β amyloid an extracellular peptide containing 40-42 amino
acid residues gets accumulated. This is neurotoxic, and is the central pathogenic
event leading to the cognitive impairment characteristic of the disease.
The Aβ that is deposited in the brain in Alzheimer disease is derived by proteolytic
cleavages from the larger amyloid precursor protein—a single transmembrane
protein expressed on the cell surface in the brain and other tissues.
The Aβ peptides aggregate, generating the amyloid that is found in the brain
parenchyma and around blood vessels.
A second biological factor involved in the development of Alzheimer disease is the
accumulation of neurofibrillary tangles inside neurons.
