Investigating Solvent Dynamics and Spin Probe Behavior Around the Intrinsically Disordered Protein β-Casein Through EPR Spectroscopy Public

Abstract

Intrinsically disordered proteins (IDPs)—those proteins that have no fixed, well-defined structure—and their dynamics within the cell are known to be important in human disease processes. Previously, globular proteins, such as ethanolamine ammonia-lyase (EAL) and myoglobin (Mb) have been studied by using electron paramagnetic resonance (EPR) spectroscopy, over the temperature range 195-265 K and at varying concentrations of dimethyl sulfoxide (DMSO) cosolvent. The paramagnetic nitroxide molecule, TEMPOL, which has EPR-detectable rotational motion—is used as a spin probe. Here, we report results for β-casein, representative of IDPs, over the temperature range 235-265 K and in the absence and presence of DMSO. EPR spectra were collected, and a Matlab algorithm was used to simulate the experiments and find the parameters (i.e., the weight and correlation times of both the fast and slow components of motion) of the best fit. Examination of temperature trends in the EPR spectra and numerical parameters reveals broad similarities in the EPR behavior of the globular and disordered proteins, but also—contrary to expectations—more rigid behavior continuing into higher temperature ranges in the β-casein system. Explanations of the protein and solvent dynamics responsible for the differing behavior are presented.

Table of Contents

I. Introduction                                                             1

II. Experimental Procedures      7

a. Essential EPR      7

b. EPR Procedures     12

c. Automatic Simulations   13

d. Manual Adjustment  14

e. Data Analysis   15

III. Results and Discussion    16

a. The Spectral Patterns of Globular and Disordered Protein   23

Systems are Highly Similar 

b. The Use of 2% DMSO Cosolvent Creates More System Mobility            23

c. Correlation Times are Similar Between Systems of     24

Globular and Disordered Proteins 

d. The Intrinsically Disordered Systems Consistently Display A More    24

Prominent Slow Component

IV. Conclusion    28

V. References    29

About this Honors Thesis

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School	Emory College
Department	Physics
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Physics, General Biophysics, General Physics, Condensed Matter
Mot-clé	Intrinsically Disordered Proteins IDP Spin Probe EPR Solvent Dynamics Zeeman Energy Electron Paramagnetic Resonance EAL Myoglobin Magnetism β-Casein
Committee Chair / Thesis Advisor	Kurt Warncke, Emory University
Committee Members	Effrosyni Seitaridou, Emory University David Lynn, Emory University

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