benjamin kelty summer research biophysics
TRANSCRIPT
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Employing Multiple Spectroscopic Techniques Simultaneously to Observe
Protein UnfoldingBen Kelty and Brennan Cull
Advisor: Dr. Justin J LinkBiophysics Program
Department of Physics
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• A protein is a chain of amino acids– Twenty different amino acids
• Proteins are essential to life– Variety of biological functions
• Catalysis, Structure, Protection (Immune System), and Regulating Cell Division
• Diseases caused by protein misfolding– Alzheimer’s Disease– Huntington’s Disease– Atherosclerosis– Type II Diabetes– Many types of cancers
Petsko, G. A., and Ringe, D. Protein Structure and Function. New Science Press, 2004. Print
Background Information
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PurposeDevelop a cost-efficient way to study the structure and stability of a protein as it unfolds
Overview of Procedure• Titration that increases the concentration
guanidine hydrochloride at each step in order to unfold the protein, cytochrome c, and a couple of its mutants
• Measure the following in one, automated scan:– Circular Dichroism (CD)– Absorbance– Fluorescence
To help support or disclaim the results of published literature
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Equine Cytochrome c
• Model System• Well characterized• Relatively small in
size• Single Tryptophan
molecule• Cofactor: Heme
group
Zang C., et al. (2009) J Am Chem Soc 131(8):2846–2852
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Equine Cytochrome c
• Foldons
Maity H., et al. (2005) PNAS 102: 4741-6
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Mutants
W89
W66W77 W72
W82
W36
W23
W102W45W15
W51
Location of the Tryptophan within Wild-Type Cytochrome c
W59
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Spectroscopic Techniques
Fluorescence monitors proximity of heme relative to tryptophan
Zang C., et al. (2009) J Am Chem Soc 131(8):2846–2852
Absorbance monitors the local environment of the heme
Circular dichroism determines the components of secondary structure
W59
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Our Contribution
• Reproduce past experiments to determine precision of parameters and conditions
• Troubleshoot technical issues• Successfully ran a scan
containing all three techniques
• Tested two mutants and compared scans to Wild-Type
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Data Analysis (Wild-Type)
320 340 360 380 400 420
0.00.10.20.30.4
GdnHCl
(M)
Wavelength (nm)
Flu
or. (
AU)
220 225 230 235 240
-100-80-60-40-200
GdnHCl (M
)Wavelength (nm)
CD
(mde
g)
380 400 420 440
0.00.20.40.60.81.01.21.4
GdnHC
l (M)
Wavelength (nm)
Abs.
(OD)
222 nm 403.1nm
350nm
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0 1 2 3 4 5-0.1
0.0
0.1
0.2
0.3
0.4
Flu
or. a
t 350
nm
GdnHCl (M)
Data Analysis (Wild-Type)
0 1 2 3 4 5-0.1
0.0
0.1
0.2
0.3
0.4
Flu
or. a
t 350
nm
GdnHCl (M)
0 1 2 3 4 50.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
Abs.
at 4
03.1
nm
GdnHCl (M)0 1 2 3 4 5
-100
-80
-60
-40
-20
0
CD a
t 222
nm
GdnHCl (M)0 1 2 3 4 5
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
Abs.
at 4
03.1
nm
GdnHCl (M)0 1 2 3 4 5
-100
-80
-60
-40
-20
0
CD a
t 222
nm
GdnHCl (M)
𝑆𝑜𝑏𝑠=(𝐶 𝑓 +𝑚 𝑓 [𝐺𝑑𝑛𝐻𝐶𝑙 ])+(𝐶𝑢+𝑚𝑢 [𝐺𝑑𝑛𝐻𝐶𝑙 ])𝑒
−Δ𝐺+𝑚𝑔[𝐺𝑑𝑛𝐻𝐶𝑙 ]𝑅𝑇
1+𝑒−Δ𝐺+𝑚𝑔[𝐺𝑑𝑛𝐻𝐶𝑙 ]
𝑅𝑇
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Data Analysis (Wild-Type)
0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
Abs. at 403.1nm (OD)
Frac
tion
Unfo
lded
GdnHCl (M)0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
CD at 222nm (mdeg)
Frac
tion
Unfo
lded
GndHCl (M)
0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
Fluor. at 350nm (AU)
Frac
tion
Unfo
lded
GdnHCl (M)
Technique ΔG (kcal/mol) Cm (M)
CD 7.83 2.30
Absorbance 7.12 2.25
Fluorescence 7.71 2.34
Published (CD) 7.27 2.42
Published (HX) 7.40 N/AKnapp, JA and Pace CN. Biochemistry 13, 1289-94. (1974).Maity, H et al. J Mol Biol 343, 223-33. (2004).
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Fraction Unfolded (Wild-Type)
Technique ΔG (kcal/mol) Cm (M)CD 7.83 2.30Absorbance 7.12 2.25Fluorescence 7.71 2.34Published (CD) 7.27 2.42Published (HX) 7.40 N/AGlobal Fit 7.83 2.30
0 1 2 3 4 5-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Individual Fit
CD Fit CD Data Abs Fit Abs Data Fluor Fit Fluor Data
Frac
tion
Unfo
lded
GdnHCl (M)0 1 2 3 4 5
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Global FIt
Global Fit CD AbsorbanceFluorescence
Frac
tion
Unfo
lded
GdnHCl (M)
Knapp, JA and Pace CN. Biochemistry 13, 1289-94. (1974).Maity, H et al. J Mol Biol 343, 223-33. (2004).
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0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
Circular Dichroism
Frac
tion
Unfo
lded
GdnHCl (M)
F82W pWT Wild-Type
0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
Global Fit
Frac
tion
Unfo
lded
GdnHCl (M)
F82W pWT Wild-Type
0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
Fluorescence
Frac
tion
Unfo
lded
GdnHCl (M)
F82W pWT Wild-Type
0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
Absorbance
Frac
tion
Unfo
lded
GdnHCl (M)
F82W pWT Wild-Type
Data Analysis Comparison
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Conclusions/Word of Advice• When in doubt buy two
replacement parts• If you are not having fun you are
doing something wrong• Do not be afraid to ask questions
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Acknowledgements
• Dr. Justin J Link• Brennan Cull and Michael Crowe• Previous Research Students• Xavier University Physics
Department
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Questions?