Actin is one of the most widespread proteins in eukaryotic cells. This book and its companion (Molecular Interactions of Actin. Actin-Myosin Interaction, Actin-Based Regulation) provide an authoritative and opinionated view of the structure and function of this essential protein. Each section includes an historical perspective and a detailed commentary on actin protein chemistry, molecular and cell biology of actin. While some chapters review the body of knowledge of the subject, others contain new experimental data. This book will appeal to research scientists seeking contemporary overviews of actin and its binding proteins. Contributors include senior scientists as well as the new breed of younger scientists.

Since the discovery of actin by Straub in the 1950’s and the pioneering work of Oosawa on actin self-assembly in helical laments in the 1960’s, many books and conference proceedings have been published. As one of the most essential p- teins in life, essential for movement in organisms rangingfrom bacteria to higher eukaryotes, it is no surprise that actin has fascinated generations of scientists from many different elds. Actin can be considered as a “living treasure” of biology; the kinetics and thermodynamics of self-assembly, the dissipative nature of actin po- merization, the molecular interactions of monomeric and polymerized actin with regulators, the mechanical properties of actin gels, and more recently the force p- ducing motile and morphogenetic processes organized by the actin nanomachine in response to signaling, are all milestones in actin research. Discoveries that directly derive from and provide deeper insight into the fundamental properties of actin are constantly being made, making actin an ever appealing research molecule. At the same time, the explosion in new technologies and techniques in biological sciences has served to attract researchers from an expanding number of disciplines, to study actin. This book presents the latest developments of these new multiscale approaches of force and movement powered by self-assembly processes, with the hope to opening our perspectives on the many areas of actin-based motility research.

This book provides a comprehensive view on actin monomer-binding proteins and the mechanisms by which they contribute to actin dynamics and various actin-dependent cellular processes. This new title contains chapters that describe the basic mechanisms of actin dynamics as well as the structural principles by which various actin-binding proteins interact with actin. The book is suitable further reading for students in advanced cell biology classes.

The regulation of filamentous actin (F-actin) production from the polymerization of globular actin (G-actin) within the cell is critical for many cell functions. Since actin is found in all cells, understanding how actin-binding-proteins (ABPs) bind and how their regulating mechanisms work is not only important to the basics of cytoskeletal pathways, but also to understanding associated diseases and creating possible therapeutics to combat them. Cofilin is an ABP that plays an important part in the regulation process and in recent times, has come to be known as a player in maintaining a cell's homeostasis. It's activity has been shown to have implications in many diseases, such as Alzheimer's and certain cancers. Cofilin binds and severs actin filaments, leading to depolymerization as well as the creation of new barbed ends. Although some of the details of cofilin's interaction with G-actin have been illuminated through a range of experimental studies, the specific interactions with F-actin have remained much more elusive. As of yet, there are only cryoEM models of cofilin-bound F-actin (where the binding occurs at a 1:1 ratio), which are not high enough resolution and do not show molecular interactions. The focus of this research is to build a model of how cofilin binds F-actin and understand the mechanism of severing. Computational methods, such as protein-protein docking, all atom molecular dynamics (AA MD) simulations, and Coarse Grain MD (CG MD) can help in understanding the interactions between cofilin and F-actin. Iteratively combining these methods with biochemical and mutagenesis experiments to reach a consensus offer a guide towards a more cogent answer. Here in this dissertation, I describe how I built a cofilin and F-actin binding model, with the aid of empirical data. This work allowed me to create several filament models with varying number of bound cofilin, which replicates different binding states of the filament. I also simulated the dynamics of these filaments models to gain insight into filament behavior, particularly twist.