The cellular function of proteins, and their targeting by drug applications, are both governed by biomolecular thermodynamics and kinetics. In order to make meaningful and efficient predictions of these mechanisms, molecular simulations must be able to estimate the binding affinity and rates of association and dissociation of a protein-ligand complex, or the populations and rates of exchange between distinct conformational states (i.e. folding and unfolding, binding and unbinding). The above studies are typically done using different, but complementary approaches. Alchemical methods, including free energy perturbation (FEP) and thermodynamic integration (TI), have become the dominant method for computing high-quality estimates of protein-ligand binding free energies. In particular, the widely-used approach of relative binding free energy calculation can deliver accuracies within 1 kcal mol−1. However, detailed physical pathways and kinetics are missing from these calculations. In principle, all-atom molecular dynamics (MD) simulation, with the help of Markov State Models (MSMs), can be used to obtain this information, yet finite sampling error still limits MSM approaches from making accurate predictions for very slow unfolding or unbinding processes. To overcome these issues, a new approach called multiensemble Markov models (MEMMs) have been developed, in which sampling from biased thermodynamic ensembles can be used to infer states populations and transition rates in unbiased ensembles. In this dissertation, two distinct biophysical problems are investigated. In the first part, we apply expanded ensemble (EE) methods to accurately predict relative binding free energies for a series of protein-ligand systems. Moreover, we propose a simple optimization scheme for choosing alchemical intermediates in free energy simulations. In the second part, we employ MEMMs to estimate the free energies and kinetics of protein folding and ligand binding, to achieve greatly improved predictions. Finally, we combine the above EE method and a maximum-caliber algorithm to study how sequence mutations perturb protein stability and folding kinetics. In summary, this work comprises a wide range of current methodology in biophysical simulation, complementing and improving upon existing approaches.

Since the first attempts to model proteins on a computer began almost thirty years ago, our understanding of protein structure and dynamics has dramatically increased. Spectroscopic measurement techniques continue to improve in resolution and sensitivity, allowing a wealth of information to be obtained with regard to the kinetics of protein folding and unfolding, and complementing the detailed structural picture of the folded state. Concurrently, algorithms, software, and computational hardware have progressed to the point where both structural and kinetic problems may be studied with a fair degree of realism. Despite these advances, many major challenges remain in understanding protein folding at both the conceptual and practical levels. Computational Methods for Protein Folding seeks to illuminate recent advances in computational modeling of protein folding in a way that will be useful to physicists, chemists, and chemical physicists. Covering a broad spectrum of computational methods and practices culled from a variety of research fields, the editors present a full range of models that, together, provide a thorough and current description of all aspects of protein folding. A valuable resource for both students and professionals in the field, the book will be of value both as a cutting-edge overview of existing information and as a catalyst for inspiring new studies. Computational Methods for Protein Folding is the 120th volume in the acclaimed series Advances in Chemical Physics, a compilation of scholarly works dedicated to the dissemination of contemporary advances in chemical physics, edited by Nobel Prize-winner Ilya Prigogine.

This book discusses a broad range of basic and advanced topics in the field of protein structure, function, folding, flexibility, and dynamics. Starting with a basic introduction to protein purification, estimation, storage, and its effect on the protein structure, function, and dynamics, it also discusses various experimental and computational structure determination approaches; the importance of molecular interactions and water in protein stability, folding and dynamics; kinetic and thermodynamic parameters associated with protein-ligand binding; single molecule techniques and their applications in studying protein folding and aggregation; protein quality control; the role of amino acid sequence in protein aggregation; muscarinic acetylcholine receptors, antimuscarinic drugs, and their clinical significances. Further, the book explains the current understanding on the therapeutic importance of the enzyme dopamine beta hydroxylase; structural dynamics and motions in molecular motors; role of cathepsins in controlling degradation of extracellular matrix during disease states; and the important structure-function relationship of iron-binding proteins, ferritins. Overall, the book is an important guide and a comprehensive resource for understanding protein structure, function, dynamics, and interaction.

Proteins perform a tremendous array of finely-tuned functions which are not only critical in living organisms, but can be used for industrial and medical purposes. The ability to rationally design these molecular machines could provide a wealth of opportunities, for example to improve human health and to expand the range and reduce cost of many industrial chemical processes. The modularity of a protein sequence combined with many degrees of structural freedom yield a problem that can frequently be best tackled using computational methods. These computational methods, which include the use of: bioinformatics analysis, molecular dynamics, empirical forcefields, statistical potentials, and machine learning approaches, amongst others, are collectively known as Computational Protein Design (CPD). Here CPD is examined from the perspective of four different goals: successful design of an intended structure, the prediction of folding and unfolding kinetics from structure (kinetic stability in particular), engineering of improved stability, and prediction of binding sites and energetics. A considerable proportion of protein folds, and the majority of the most common folds ("superfolds"), are internally symmetric, suggesting emergence from an ancient repetition event. CPD, an increasingly popular and successful method for generating de novo folded sequences and topologies, suffers from exponential scaling of complexity with protein size. Thus, the overwhelming majority of successful designs are of relatively small proteins ( 100 amino acids). Designing proteins comprised of repeated modular elements allows the design space to be partitioned into more manageable portions. Here, a bioinformatics analysis of a "superfold", the beta-trefoil, demonstrated that formation of a globular fold via repetition was not only an ancient event, but an ongoing means of generating diverse and functional sequences. Modular repetition also promotes rapid evolution for binding multivalent targets in the "evolutionary arms race" between host and pathogen. Finally, modular repetition was used to successfully design, on the first attempt, a well-folded and functional beta-trefoil, called ThreeFoil. Improving protein design requires understanding the outcomes of design and not simply the 3D structure. To this end, I undertook an extensive biophysical characterization of ThreeFoil, with the key finding that its unfolding is extraordinarily slow, with a half-life of almost a decade. This kinetic stability grants ThreeFoil near-immunity to common denaturants as well as high resistance to proteolysis. A large scale analysis of hundreds of proteins, and coarse-grained modelling of ThreeFoil and other beta-trefoils, indicates that high kinetic stability results from a folded structure rich in contacts between residues distant in sequence (long-range contacts). Furthermore, an analysis of unrelated proteins known to have similar protease resistance, demonstrates that the topological complexity resulting from these long-range contacts may be a general mechanism by which proteins remain folded in harsh environments. Despite the wonderful kinetic stability of ThreeFoil, it has only moderate thermodynamic stability. I sought to improve this in order to provide a stability buffer for future functional engineering and mutagenesis. Numerous computational tools which predict stability change upon point mutation were used, and 10 mutations made based on their recommendations. Despite claims of 80% accuracy for these predictions, only 2 of the 10 mutations were stabilizing. An in-depth analysis of more than 20 such tools shows that, to a large extent, while they are capable of recognizing highly destabilizing mutations, they are unable to distinguish between moderately destabilizing and stabilizing mutations. Designing protein structure tests our understanding of the determinants of protein folding, but useful function is often the final goal of protein engineering. I explored protein-ligand binding using molecular dynamics for several protein-ligand systems involving both flexible ligand binding to deep pockets and more rigid ligand binding to shallow grooves. I also used various levels of simulation complexity, from gas-phase, to implicit solvent, to fully explicit solvent, as well as simple equilibrium simulations to interrogate known interactions to more complex energetically biased simulations to explore diverse configurations and gain novel information.

Computer-based design and modeling, computational approaches, and instrumental methods for elucidating molecular mechanisms of protein folding and ligand-acceptor interactions are included in Volumes 202 and 203, as are genetic and chemical methods for the production of functional molecules including antibodies and antigens, enzymes, receptors, nucleic acids and polysaccharides, and drugs.

Computational structural biology has made tremendous progress over the last two decades, and this book provides a recent and broad overview of such computational methods in structural biology. It covers the impact of computational structural biology on protein structure prediction methods, macromolecular function and protein design, and key methods in drug discovery. It also addresses the computational challenges of experimental approaches in structural biology. In addition to reviewing the current state of computational structural biology, each chapter ends with a brief, visionary discussion on the future outlook, whereby the main challenges for the coming years are elucidated. Written by an international panel of expert contributors, this book can serve as a reference manual for students and practitioners alike.

Computational Approaches for Understanding Dynamical Systems: Protein Folding and Assembly, Volume 170 in the Progress in Molecular Biology and Translational Science series, provides the most topical, informative and exciting monographs available on a wide variety of research topics. The series includes in-depth knowledge on the molecular biological aspects of organismal physiology, with this release including chapters on Pairwise-Additive and Polarizable Atomistic Force Fields for Molecular Dynamics Simulations of Proteins, Scale-consistent approach to the derivation of coarse-grained force fields for simulating structure, dynamics, and thermodynamics of biopolymers, Enhanced sampling and free energy methods, and much more. Includes comprehensive coverage on molecular biology Presents ample use of tables, diagrams, schemata and color figures to enhance the reader's ability to rapidly grasp the information provided Contains contributions from renowned experts in the field