chapter 3 exploring proteins and proteomes
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Chapter 3 Exploring Proteins and Proteomes. Genome. A collective name for the genes existed in an organism C. elegance (roundworm) : 97 million bases, 19,000 genes Drosophila melanogaster (fruit fly) : 180 million bases, 14,000 genes Human : 3 billion bases, 23,000 genes - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 3
Exploring Proteins and Proteomes
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• A collective name for the genes existed in an organism
• C. elegance (roundworm) : 97 million bases, 19,000 genes
Drosophila melanogaster (fruit fly) : 180 million bases, 14,000 genes
Human : 3 billion bases, ~20,000 genes
• Static and absolute information
Genome
• A collective name for the proteins expressed by the genome
• Dynamic and functional information
• It varies with cell type, developmental stage, and environmental condition
such as the presence of hormones.
• Regulation of mRNA synthesis, alternative splicing, mRNA stability, rate of
protein synthesis, post-translational modification, protein stability control,
protein degradation
Proteome
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• The purification of proteins is an essential first step in understanding their
function.
• Purification should yield a sample of protein containing only one type of
molecule of interest.
• Proteins can be separated from one another on the basis of solubility, size,
charge, and binding ability.
• Assay : a test for some unique identifying property of the protein
• Specific Activity : the ratio of enzyme activity to the amount of protein in the
enzyme assay
Protein Purification
NADHcan absorb light
at 340 nm.
Nicotinamide adenine dinucleotide
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Homogenation and Fractionation by Centrifugation
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• Salting Out : protein solubility decrease by very high concentration of salt
• Salting In : protein solubility increase by low concentration of salt
• Dialysis : separation of small molecules from proteins through membrane with
pores such as cellulose membrane (cf. semi-permeable)
Salting Out & Dialysis
Ammonium sulfate for protein precipitation
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Gel-Filtration Chromatography(Molecular Exclusion,
Size Exclusion,Molecular Sieve)
1. Thyroglobulin (669 kd)
2. Catalase (232 kd)
3. BSA (67 kd)
4. Ovalbumin (43 kd)
5. Ribonuclease (13.4 kd)
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Anion ExchangerPositively Charged Column
Negatively Charged Proteins
Cation ExchangerNegatively Charged ColumnPositively Charged Proteins
Ion-ExchangeChromatography
Depend on local charge on proteins
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LCLiquid Chromatography
FPLCFast Pressure Liquid Chromatography
HPLCHigh Pressure Liquid Chromatography
AffinityChromatography
(concanavalin A)
Highly specific- Histidine tag
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Gel Electrophoresis
v = Ez / fv : velocity of migrationE : electric field strength
z : net charge on the proteinf : frictional coefficient
f = 6r : viscosity of the medium
r : radius of the protein
Polyacrylamide gel electrophoresis
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Polymer Formation of Acrylamide using Bis-Acrylamidefor PAGE (Poly-Acrylamide Gel Electrophoresis)
AmmoniumPersulfate
Sieving action!
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SDS-PAGE : Denaturing Gel(Determination of the Molecular Weight of Protein)
Coomassie Blue Staining; > 0.1 g)(cf. Silver Staining: > 0.02 g)
Under BME, DTT
One SDS anion for every two a.a.
Except carbohydrate-rich proteins, membrane proteins
Mobility ; Log of MWResolution: 2% MW difference
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Isoelectric Focusing & Two Dimensional Electrophoresis
pI : Isoelectric Point (pH with net charge zero)
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Evaluation of Protein Purification
As purification continues, relative presence of
contaminants should be decreased and
the proportional amount of the protein of
interest should be increased.
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Centrifugation & Sedimentation Coefficient
• A more massive particle sediments more rapidly.
• A more compact shaped particle sediments faster.
(i.e. elongated particles sediments more slowly than do
spherical ones of the same mass. Frictional coefficient
f)
• A denser particle sediments more rapidly. Buoyant
force is smaller for the denser particle
• v < 1 : sink, v > 1 : float, v = 1 : no movement
s = m(1 - v) / fs : sedimentation coefficient
m : mass of the particle
v : partial specific volume; the reciprocal of the particle density : density of the medium
(1 - v) : buoyant force exerted by liquid medium
f : frictional coefficient; a measure of the particle shape
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a. Seidmentation process in the cell
From Archimedes’ principleBuoyancy = weight of displaced fluid
Or fluid density x submerged vol x g
Principle of Analytical Ultracentrifugation
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b.solute distribution in the cell
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S Value for Various Proteins
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Density and Sedimentation Coefficient
for Various Cellular Components
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Gradient (Zonal or Band) Centrifugation:
Separation of Non-Denatured Proteins with different sedimentaion coefficients
(Size, Density and Shape)
Sedimentation equilibrium: centrifuged at low speed so that sedimentation is counter balanced by diffusion-Very accurate in mass determination without denaturing.- useful for large multimeric proteins.
Sedimentation velocity
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Determination of Amino Acid Composition of the Peptide
1. Peptide hydrolyzation by heating it in 6N HCl at 100oC for 24 hrsAla-Gly-Asp-Phe-Arg-Gly
(Asp, Gly2, Ala, Phe, Arg)
2. Separation of amino acid hydrolysates by ion-exchange chromatography (e.g. sulfonated polystyrene resin; Dowex-50)
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3A. Quantitation of Each Fraction by Ninhydrin;Yield Visible Color (usually blue except Pro for yellow);Detection Sensitivity = Microgram (10 nmol) of an Amino Acid
3B. Quantitation of Each Fraction by Fluorescamine;Yield Fluorescence;Detection Sensitivity = Nanogram (10 pmol) of an Amino Acid
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Identification of N-Terminal Amino Acid
(FDNB) YieldFluorescentSulfonamide
FDNB, Dabsyl Chloride, or Dansyl Chloride
Can Specifically React with the N-terminal Amino Group, and
Yield DNB-Amino Acid, Dabsyl Amino Acid, or Dansyl Amino Acid, and
These Can Be Identified by Their Chromatographical Properties.
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Determination of Amino Terminal Residue of a Peptideusing Dabsyl Chloride
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Edman Degradation Sequentially Removes One Residue at a Timefrom the Amino End of a Peptide up to 50 times
Each round
can be complete
within 1 hr and
the Edman degradation
can be repeated
up to 50 cycles
in Practice.
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Phenyl Isothiocyanate (PITC) Can Specifically React with
the N-terminal Amino Group, and Yield Phenyl Thiocarbamoyl (PTH) Amino Acid,
and This Can Be Identified by Its Chromatographical Property.
Separation of PTH-Amino Acids
Current Sensitivity ofPTH-AA Detection UsingGas-Phase Sequenator:
Picomole
Mild acidic condition
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For sequencing of an entire Protein…??Divide and Conquer !!!
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Sequence Specific Cleavage by Cyanogen Bromide
Sequence Specific Cleavage by Trypsin
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Deduction of Full Amino Acid Sequence of a Proteinby Overlapping the Sequences Obtained from individual Peptides
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Reduction of Disulfide Bonds :
-Mercaptoethanol, Dithiothreitol (DTT)
Sequencing of Multimeric Proteins
Denaturation :
Urea, Guanidium Chloride, SDS
Preservation of Reduced Sulfhydryl Groups :
Alkylation using Iodoacetate
Separation of Each Polypeptide Chain :
SDS-PAGE
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Diagonal Electrophoresisto Determine the Positions of the Disulfide Bonds
Reduction and Oxidation of Disulfide Bonds by Performic Acid
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The Amino Acid Sequence Provides Insightsinto the Protein’s Function, Structure, and History
1. The sequence of a protein of interest can be compared with all other known
sequences to ascertain similarities. (Family, function prediction possible)
2. Comparison of sequences of the same protein in different species yields a wealth
of information about evolutionary pathway.
3. Amino acid sequences can be searched for the presence of internal repeats.
4. Many proteins contain amino acid sequences that serve as signals designating
their destinations or controlling their processing. (N-terminal 20 hydrophobic
residues, signal sequence, nuclear localization signal)
4 Repeating Motifs
in Calmodulin :
Each Unit Binds
a Calcium Ion
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• Amino acid sequence data provide a basis for preparing antibodies specific for a
protein of interest.
• Amino acid sequence are valuable for making DNA probes that are specific for the
genes encoding the corresponding proteins.
• The nucleotide sequence of DNA (gene) directly reveals the entire amino acid
sequence of the protein encoded by the gene.
• However, DNA sequence can not disclose the information regarding post-translational
modification.
Practical Usage of Amino Acid and DNA Sequences
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Antibody
• Antibody (immunoglobulin) is a protein synthesized by an animal in response to the
presence of a foreign substance (antigen).
• Antibodies have specific and high affinity against antigens.
• Proteins, polysaccharides and nucleic acids can be effective antigens.
• Epitope : a specific group or cluster (portion) of antigen to stimulate the synthesis of an
antibody and recognized by a specific antibody (antigenic determinant)
• Hapten : a small molecule containing epitope attached to a carrier
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Antibody (continued)
• Each antibody producing cell synthesizes only one type of
antibody recognizing a single kind of epitope.
• The proliferation of a given antibody producing cell is
stimulated by the binding of its designated antigen to the cell
surface receptor of the antibody producing cell .
• Periodic injections of an antigen into the host animal can raise
the antibodies specifically recognizing the injected foreign
substance.
• Blood withdrawn from the immunized host animal
centrifugation separation of blood cells (pellet) and serum
(supernatant) anti-serum
• Anti-serum contains multiple kinds of antibodies each
recognizing a different surface feature of the same antigen.
• This heterogenic antibodies are called as polyclonal antibodies.
• This heterogeneity can complicate the use of these antibodies.
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Monoclonal Antibody
• Monoclonal hybridoma cell lines can generate large amount of homogeneous antibodies.
• Monoclonal antibodies can serve as precise analytical, preparative and therapeutic reagents.(HCV, HIV, herceptin)
Immuno-Staining ofDrosophila
Embryousing
MonoclonalAntibodyagainst
Engrailed
Plasma cell
by antigen-antibody interaction
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Monoclonal antibody drugs?
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Herceptin Binds to the C-terminus of Domain IV
Herceptin Fab
I
III
II
IV
N
C
HER2
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Ribbon Diagram of Her-3 ECD
N
C
“Tethered”I
II
III
IV
Right-handed helixLaminin-like folds
Fig. 14.28 pp397
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Surface representations of EGFR and HER2 in Antibody-Bound Conformations
Herceptin
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ELISA (Enzyme-Linked Immuno-Sorbent Assay)
Antibody detection, anti-HIV antibody
Antigen detection
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Western Blotting
Radioactive secondary antibody
For protein expression and purification
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Immuno-FluorescenceMicroscopy
Actin Filament Stainingusing -actin antibody
Immuno-ElectronMicroscopy
Detection of a channel proteinfrom the synaptic vesicles
using antibodies tagged withelectron-dense markers such as gold or
ferritin(Resolution better than 10 nm)
Fluorescence-labeled antibodies(resolution 200nm)
ex) Glucocorticoid receptor
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Synthetic Peptides
• Synthetic Antigens for antibody formation• Receptor or Interacting Protein Isolation• Clinical Drugs (ex, vasopressin)• 3D Structure Study
• Increase water absorption in the kidney; Aquaporin • Caffeine decreasesrelease of AVP
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Protection of Amino Groupby t-BOC
Activation of Carboxyl Groupby DCC
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Solid Phase
Peptide Synthesis
(more than 100 amino acids)
Resin : Insoluble Matrix (Polystyrene Beads), HF : Hydrofluoric Acid
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MALDI-TOFMass
Spectrometry
MALDI : Matrix-AssistedLaser Desorption-Ionization
TOF : Time of FlightF=ma
Mass Spectrometry
Are Often Combined with
2D Electrophoresis
for Proteome Analysis
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h
Laser
+20 kV
Variable Ground Grid Grid
AH+
Sample plate 1. Sample (A) is mixed with excess matrix (M) and dried on a MALDI plate.
2. Laser flash ionizes matrix molecules.
3. Sample molecules are ionized by proton transfer from matrix:
MH+ + A M + AH+.
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Why MALDI?
-Less sensitive to salts-Lower PRACTICAL detection limits-Easier to interpret spectra(less multiple
charges)-Quick and easy-Higher mass detection-Higher Throughput(1000>samples per
hour)
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The Mass Analyzer: TOFTime Of Flight(TOF)
Flight TubeIon Source
Principle: If ions are accelerated with the same potential at a fixed point and a fixed initial time and are allowed to drift, the ions will
separate according to their mass to charge ratios.
20-25 kV
++
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• Peptide can be sequenced by MS
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Individual proteins can be identified by MS
• Protein cleavage, followed by chromatographic separation and MS
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NMR (Nuclear Magnetic Resonance)
• Basis for Resolution : Electron (Proton) Chemical Shift in Magnetic Field
• Advantage
- Solving Protein Structures in Solution State
- Requires Smaller Quantity for Analysis than X-ray Crystallography
• Limitations
- Technical Difficulties for Bigger Size Proteins (> 40 kD)
- Technical Difficulties for Multi-Subunit Proteins
X-Ray Crystallography• Basis for Resolution : X-Ray Diffraction and Electron Scattering
• Advantage
- No Size Limitation for Analysis
- Solve the Structure of Multi-Subunit Complexes
• Limitations
- Solving Protein Structures in Solid State
- Difficulties in Making Protein Crystals with Good Diffraction Properties
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