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Proteins function as ensembles of interconverting structures. The motions span from picosecond bond rotations to millisecond and longer subunit displacements. Characterization of functional dynamics on all spatial and temporal scales remains challenging experimentally. Two-dimensional IR spectroscopy (2D IR) is maturing as a powerful approach for investigating proteins and their dynamics. This document outlines the advantages of IR spectroscopy, describes 2D IR and the information it provides, and introduces vibrational groups for protein analysis. Following this introduction, example studies are presented that illustrate the power and versatility of 2D IR for characterizing protein dynamics. The thesis concludes with a brief discussion of the outlook for biomolecular 2D IR.
Complete understanding of protein function requires knowledge of protein conformational dynamics, or the structural fluctuations of a protein. However, characterization of protein dynamics is challenged by protein complexity, as they are large, heterogeneous molecules with potentially important motions on very fast timescales. This complexity demands the use of a technique with high spatial and temporal resolution. Two-dimensional infrared (2D IR) spectroscopy has emerged as a powerful tool for the characterization and direct measurement of molecular heterogeneity and dynamics due to its excellent spatial and temporal resolution. However, application to proteins is hindered by their severely congested spectra due to the large number of similar bonds. To overcome this issue, proteins can be site-specifically labeled with spectrally resolved IR probes that are active in the transparent frequency region (~1800 - 2500 cm-1) and are sensitive to their environment. The studies presented here take advantage of the combination of site-specific labeling and IR spectroscopy to study the environments and dynamics at specific locations in three distinct protein systems. Herein, I describe our investigations of dynamic complexes of proteins that have challenged experimental characterization with conventional methods: plastocyanin (Pc) and its binding partner cytochrome f (cyt f); cytochrome P450cam (P450cam) and substrates or its redox partner, putidaredoxin; and the SH3Sho1 domain and the proline-rich (PR) recognition motif of its binding partner Pbs2. In addition, we describe my attempts at improving the experimental technique of site-specific IR spectroscopy as a general biophysical approach for protein characterization. Overall, I present evidence for the importance of fast dynamics in protein function and illustrate the rich information provided by 2D IR spectroscopy to complement existing biophysical methods.
Two-Dimensional Optical Spectroscopy discusses the principles and applications of newly emerging two-dimensional vibrational and optical spectroscopy techniques. It provides a detailed account of basic theory required for an understanding of two-dimensional vibrational and electronic spectroscopy. It also bridges the gap between the formal developm
2D infrared (IR) spectroscopy is a cutting-edge technique, with applications in subjects as diverse as the energy sciences, biophysics and physical chemistry. This book introduces the essential concepts of 2D IR spectroscopy step-by-step to build an intuitive and in-depth understanding of the method. This unique book introduces the mathematical formalism in a simple manner, examines the design considerations for implementing the methods in the laboratory, and contains working computer code to simulate 2D IR spectra and exercises to illustrate involved concepts. Readers will learn how to accurately interpret 2D IR spectra, design their own spectrometer and invent their own pulse sequences. It is an excellent starting point for graduate students and researchers new to this exciting field. Computer codes and answers to the exercises can be downloaded from the authors' website, available at www.cambridge.org/9781107000056.
The advent of laser-based sources of ultrafast infrared pulses has extended the study of very fast molecular dynamics to the observation of processes manifested through their effects on the vibrations of molecules. In addition, non-linear infrared spectroscopic techniques make it possible to examine intra- and intermolecular interactions and how such interactions evolve on very fast time scales, but also in some instances on very slow time scales. Ultrafast Infrared Vibrational Spectroscopy is an advanced overview of the field of ultrafast infrared vibrational spectroscopy based on the scientific research of the leading figures in the field. The book discusses experimental and theoretical topics reflecting the latest accomplishments and understanding of ultrafast infrared vibrational spectroscopy. Each chapter provides background, details of methods, and explication of a topic of current research interest. Experimental and theoretical studies cover topics as diverse as the dynamics of water and the dynamics and structure of biological molecules. Methods covered include vibrational echo chemical exchange spectroscopy, IR-Raman spectroscopy, time resolved sum frequency generation, and 2D IR spectroscopy. Edited by a recognized leader in the field and with contributions from top researchers, including experimentalists and theoreticians, this book presents the latest research methods and results. It will serve as an excellent resource for those new to the field, experts in the field, and individuals who want to gain an understanding of particular methods and research topics.
Understanding the structure and dynamics of proteins is essential to understanding their roles and functions in these physiological processes. In this thesis, I describe the implementation of an ultrafast nonlinear spectroscopic technique, two-dimensional infrared (2D IR) spectroscopy to probe the structure and dynamics of ion channels and amyloid fibers. Regarding ion channels, I describe the combination of semisynthesis, 2D IR spectroscopy and molecular dynamic (MD) simulations in addressing the longstanding question of ion permeation through the selectivity filter of a potassium ion channel. I show that ions and water alternate through the filter and that these ions cannot occupy adjacent binding sites. Furthermore, 2D IR experiments revealed a flipped state that is predicted by MD simulations but not observed in x-ray crystallography. In another aspect of this work, we show that the collapsed state of the filter is structurally different in low K+ and low pH. Moreover, our work also reveals how the large conformational motions of the protein are coupled to structural changes in the selectivity filter, as evidenced by a change in the ion occupancy. In a second research direction, I developed an optical technique to quantify photoactivatable fluorophores with fluorescence microscopy. This technique allows for the quantification of a limitless number of fluorophores, and corrects for stochastic events such as fluorescence intermittency. This work can be extended to the study of amyloids, where determining the number of proteins in a prefibrillar aggregates is necessary for understanding their roles in amyloid related diseases. Finally, using 2D IR spectroscopy we describe the effect of common solvents on the anharmonicity of small molecule chromophores. The data indicates that the carbonyl anharmonicity, and, subsequently, the Stark tuning rate, is an intrinsic property of the carbonyl vibrational probes, which have important implications on the interpretation of carbonyl vibrational frequency shifts in the condensed phase.
This book embraces all physiochemical aspects of the structure and molecular dynamics of water, focusing on its role in biological objects, e.g. living cells and tissue, and in the formation of functionally active structures of biological molecules and their ensembles. Water is the single most abundant chemical found in all living things. It offers a detailed look into the latest modern physical methods for studying the molecular structure and dynamics of the water and provides a critical analysis of the existing literature data on the properties of water in biological objects. Water as a chemical reagent and as a medium for the formation of conditions for enzymatic catalysis is a core focus of this book. Although well suited for active researchers, the book as a whole, as well as each chapter on its own, can be used as fundamental reference material for graduate and undergraduate students throughout chemistry, physics, biophysics and biomedicine.
In this thesis, dynamics experiments are developed that can be used to study protein conformational changes such as folding and binding. Every functional motion of a protein is inextricably linked to conformational dynamics. However, most of our insight into protein folding and binding is indirectly obtained through kinetics experiments that measure reaction rates and reveal how fast populations of stable states interconvert. Two-dimensional infrared spectroscopy (2D IR) is the central tool developed in this thesis for protein dynamics experiments due to its combination of time and structural resolution. As a vibrational spectroscopy, 2D IR potentially offers femtosecond time resolution. Its advantages over linear, absorption spectroscopy come through correlating excitation and emission frequencies to allow for a separation of homogenous and inhomogeneous line shape components, and to give rise to structurally sensitive cross-peaks. One general problem was repeatedly addressed in this thesis: how can 2D IR spectra best be modeled to reveal atomistic structural information? The key feature that now sets 2D IR apart from other fast protein probes is that the data can readily be calculated from an atomistic structure or molecular dynamics simulation using the methods developed in this thesis work. Demonstrative applications are presented for the amide 1-11 spectroscopy of NMA, the amide 1'-II' spectroscopy of poly-L-lysine, isotope-edited 2D IR spectroscopy of trpzip2, and transient 2D JR spectroscopy of ubiquitin unfolding after a temperature jump. The emerging paradigm is to interpret 2D IR spectra with the aid of an atomistic, molecular dynamics simulation. The applications to protein binding use the monomer-dimer transition of insulin as a model system. Using a combination of experiments and simulations, this equilibrium was characterized as a function of protein concentration, temperature, and solvent. Finally, as a complement to the structural information provided by 2D IR, dye-labeling and intrinsic tyrosine fluorescence experiments on insulin are described.